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Patrick Turner
 
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Default 2A3 - Really a beautiful power tube!

I finally have hooked up the stereo amp which uses 2A3
to my speakers which are about 90dB sensitivity.
I find I could listen all day and night to this underpowered
amplifier.
Whatever its doing it is doing it RIGHT.

The conditions are as follows.

Power tranny is Hammond type 370FX, and with
a 240V: 2 x 2.5V filament tranny.
Hammond 10H choke used with a quad of Sonic Frontier
PS caps of 1,100 uF each, so that with seriesed caps
I have 550uF, 10H, 550uF, as the CLC to supply power to the
pair of amp channels.
Rectifiers are IN5408 SS diodes. I don't strictly believe in tube
rectifiers;
I like them, I even use them sometimes; I just don't think they are
indispensible.
But in this case the use of a tube rectifier would have reduced the
available B+
and forced me to use fixed bias, which I don't like for any SE amps.

No need to dual mono power supplies.
180uF used to further filter the input and driver stages.


Output tubes are 2A3, RCA, NOS?, maybe used, not sure.
Ea = +270V, Ia = 57mA, cathode bias with 820ohms
bypassed with good quality 100V x 470uF.
heaters are AC 2.5V with a pot for hum nulling.

OPT is a 2.5k : 4/8/16 Hammond 25 watt rated SET gapped OPT
type 1627SE.

OPT is set up to match 2.5k to 4ohms, but I find 5 ohms is the most
correct load.

At 4Watts I get excellent open loop BW with this OPT
and freedom from saturation, of which there is only a slight trace at
about
7 Hz.

The OPT has queer resonances above 30kHz, makinf the use of
global NFB difficult for ppl with no clue about how to overcome such
connundrums.
It must be due to primary being wound close to the secondary,
and the absence of enough interleavings of windings, and the absence of
sufficient
insulation thickness.
Nevertheless, the 1627SE did turn out to be very usable, and sound is
glorious.

Driver tube is an ancient Radiotron 'made in australia' 6SN7,
used but OK. 1k Rk bypassed with 470uF, RL = 34k, 0.47 uF Wima coupling
cap,
150k grid bias R for 2A3, 1.8k series grid stopper.

The 6SN7 is operating fairly linearly and comfortably.
Without Ck bypass, the driver thd reduces, but then overall thd rises
a lot since less even order Dn cancelation takes place.

The fully bypassed Rk on the 6SN7 gives lowish Ra of about 5k for the
paralleled tube
and is thus a sufficiently low enough drive resistance to enhance the
micro detail behaviour of the
2A3, ( very necessary imho to get the best out of not just a triode
output tube,
but ALL output tubes.)

The input tube is 1/2 a 12AU7 of unknown lineage; it measured nicely,
and I like the 12AU7 for inputs; its warm, accurate, and sounds
glorious.

Its Rk is 1.8k, and also bypassed with 470uF, and taken then to 100 ohms
for
the global NFB to be applied.
RL is 50k, 0.47uF to a network for LF gain stepping, 1M+0.033uF
plus 220k, typical in many of my amps to vastly
improve the bass stability when the 12dB of global FB is applied.

The FB resistor divider network is 750 ohms to 100 ohms
with a phase tweaker bypass cap across the 750 ohms = 1,000 pF.
There is a 470pF plus 2.7k zobel network connected from the
driver grid to 0V to control the HF gain and ultimate phase shift of the

12AU7 to 6SN7 interface.
A further 5.6ohms+0.47uF Zobel network is across the OPT secondary,
and finally I got the amp to be fairly ring free when connected to
any value of cap without a pure R load, and when using a square wave.
Open loop BW with all compensation zobels in place was 20Hz to 20kHz,
-3dB,
and with 12 dB of FB the full power BW is 5Hz to 55kHz, 5 ohms.
It remains the same at lower levels of power.

A 5 kHz square wave is a bit ragged due to the mentioned OPT design
simplicity,
but the sine wave response between 30Hz and 20hHz right up to clipping
is dead flat.

A 50k Alps Black pot is used for the gain control.

Input sensitivity with 12dB applied global NFB is 0.7Vrms.
The amp's use with an CD player is fine.
Just no need for any preamp.

The sound is that of a far more powerful amplifier,
with tremendous sense of rightness, instrument detail, warmth without
muddle, not the slightest hint of any lack of bass, the usual beautiful
mids, and detailed top end.

The amp measures well at less than 1% thd at 4 watts into 5 ohms,
mainly all 2H.
But at normal levels of a watt the 3H and other H are present below the
2H
which can be seen on the CRO when monitoring the THD at all levels.
Ro is 0.47 ohm, and although my speakers vary between
4 and 20ohms, the sound appears firm, well timbred, and there isn't any
hint
of the sound being that from an inadequate amplifier.

I played Handel's water music, the sound track of 'The Pianist' for my
tests plus
a not so wonderful Naxos CD, 'The Best of Bach'.

Who says SET amps suck?

Certainly not I!.

Methinks that if the owner wanted more power, he could simply swap the
2A3 for a KT90 since the PT has a 6.3V heater winding, and then
remove the series R I have placed in the B+ lines to trim the B+
to where I want it, and with 270V, and with the UL tap on the
OPT that is provided, maybe 9+ watts of SEUL would be available.

The now unused 1670 OPT UL tap is at 40%.
But it could be at 60%, if you use the plate winding reversed,
thus further drifting a tetrode towards triode, but still not
suffering a huge loss of power due to grid current limitations.

300B could also be used, and with slightly more Ia,
but with the same low Ea, thus suiting moderate power and good matching
to
low value loads, which is a major failing in many SET amps;
they try to match so max power is at 8ohms, but that is
nearly always wrong with modern speakers, and
max power should occur at 3 or 4 ohms.


Patrick Turner.




  #2   Report Post  
Sander deWaal
 
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Default

Patrick Turner said:

The sound is that of a far more powerful amplifier,
with tremendous sense of rightness, instrument detail, warmth without
muddle, not the slightest hint of any lack of bass, the usual beautiful
mids, and detailed top end.



See, I told ya so.

Now put 2 of them in push/pull and enjoy them even more :-)

--

"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005
  #3   Report Post  
Bret Ludwig
 
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In passively-crossed-over, or worse, single driver systems, I have
never heard a SE tube amp that sounded better than a probperly designed
and built push pull one. I can't categorically deny the possibility of
their existence, but I have heard a LOT of homebrew SET amps and their
full range performance has been universally mediocre at best.

I will concede that given a OPT specifically designed for the job a
SET might work well for a tweeter amp in a bi-amped (true bi-amped,
actively crossed-over-NOT musketeered!) setup. Such a OPT doesnt exist
and despite lip service from several known suppliers (besides the known
sociopath from Philly, who is not credible on any level anywhere) no
such part exists. They admit (substantially) all their customers are
electro-ignoramuses who can BARELY build a SET, let alone any more
sophisticated amplifier, and are running full range because it's simple
and gives 'the rolled-off "antique radio tone" they love'-i.e. the
antithesis of high fidelity.

  #4   Report Post  
Bret Ludwig
 
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Bret Ludwig wrote

snip

I will concede that given a OPT specifically designed for the job a
SET might work well for a tweeter amp in a bi-amped (true bi-amped,
actively crossed-over-NOT musketeered!) setup. Such a OPT doesnt exist
and despite lip service from several known suppliers (besides the known
sociopath from Philly, who is not credible on any level anywhere) no
such part exists.


Oops.


I meant to say "they have no desire to make one", or, "no such _desire
or intent to make any_ such part exists". Because despite the talk, the
walk is they are barely smart enough to build a crystal radio. Their
construction skills are below what 12-year-old boys demonstrated from
the 1930s to the 1960's.

(Fortunately, a depression seems imminent, which should give them
plenty of time to study and practice.)

  #5   Report Post  
Mark Harriss
 
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Default

Bret Ludwig wrote:
Bret Ludwig wrote

snip

I will concede that given a OPT specifically designed for the job a
SET might work well for a tweeter amp in a bi-amped (true bi-amped,
actively crossed-over-NOT musketeered!) setup. Such a OPT doesnt exist
and despite lip service from several known suppliers (besides the known
sociopath from Philly, who is not credible on any level anywhere) no
such part exists.



Oops.


I meant to say "they have no desire to make one", or, "no such _desire
or intent to make any_ such part exists". Because despite the talk, the
walk is they are barely smart enough to build a crystal radio. Their
construction skills are below what 12-year-old boys demonstrated from
the 1930s to the 1960's.

(Fortunately, a depression seems imminent, which should give them
plenty of time to study and practice.)


So who are you deliberately insulting here Bret?, the home constructors
or the transformer winders?.


  #6   Report Post  
Bret Ludwig
 
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Default

Mostly the home constructors, the xfmr winders build what they can
sell.

  #7   Report Post  
Patrick Turner
 
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Default



Sander deWaal wrote:

Patrick Turner said:

The sound is that of a far more powerful amplifier,
with tremendous sense of rightness, instrument detail, warmth without
muddle, not the slightest hint of any lack of bass, the usual beautiful
mids, and detailed top end.


See, I told ya so.

Now put 2 of them in push/pull and enjoy them even more :-)


The owner wants the 2A3amps to power some JBL bullet horns from 6kHz and
up.

Kinda bein' easy on the amps, eh.

And now he's got a pair of Tannoy 15" Gold Monitors,
corner boxes, as well as the horns.

I think his horns sound better.

Patrick Turner.



--

"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005


  #8   Report Post  
Patrick Turner
 
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Default



Bret Ludwig wrote:

In passively-crossed-over, or worse, single driver systems, I have
never heard a SE tube amp that sounded better than a probperly designed
and built push pull one. I can't categorically deny the possibility of
their existence, but I have heard a LOT of homebrew SET amps and their
full range performance has been universally mediocre at best.


Ah well, maby you have not heard the best of what SE amplifiers can
provide.

I used to think all horns shouted or honked, until I heard a system that
was well set up.



I will concede that given a OPT specifically designed for the job a
SET might work well for a tweeter amp in a bi-amped (true bi-amped,
actively crossed-over-NOT musketeered!) setup. Such a OPT doesnt exist
and despite lip service from several known suppliers (besides the known
sociopath from Philly, who is not credible on any level anywhere) no
such part exists.


I think the SE OPT from Hammond is quite ok for full range.
With a properly damped and set up amp the F response of the finished
2A3 was 5Hz to 55kHz at full power.

There is no reason why an amp designed for full range and with an OPT
suitable for bass won't also have a good to end.
I have routinely wound OPTs capable of 10Hz to 300kHz
at full power.
Its just a matter of turns, interleaving, and the insulation,
and about 50 calculations.

But even the simplest and cheapest OPT available off the shelf such as a
1670SE
from Hammond manages to give good enough bandwidth even without loop FB.


They admit (substantially) all their customers are
electro-ignoramuses who can BARELY build a SET, let alone any more
sophisticated amplifier, and are running full range because it's simple
and gives 'the rolled-off "antique radio tone" they love'-i.e. the
antithesis of high fidelity.


Well none of the ppl I know have systems with restricted bandwidth.
That old dumpy "valve sound" simply *is not* what they like.

All the ppl I know are fanatics about the sound quality of their systems.
Some can't solder, and can't understand Ohm's Law, but they
are *NOT* ignoramuses.

Patrick Turner.



  #9   Report Post  
Karl
 
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Default


Bret Ludwig wrote:
Mostly the home constructors, the xfmr winders build what they can
sell.


Lots of winders will make whatever you want. You can spec *anything*
with some of them. Like the Rutles said: All you need is cash.

  #10   Report Post  
Bret Ludwig
 
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Default


Lots of winders will make whatever you want. You can spec *anything*

with some of them. Like the Rutles said: All you need is cash.



If you will buy enough of them that is somewhat true. I had one place
that does a lot of secure sonar work offer to make me some MC240
outputs-but they wanted a quantity 1000 order. I replied that I dodn't
think they had ever made 1000 of anything in the last 40 years.

Their reply? "We haven't. But you aren't going to call us up five
years from now and demand one more at a 5X rush charge, and the Navy
will. For you, it's a thousand or none".



  #11   Report Post  
Accessory Section 8
 
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Default


Bret Ludwig wrote:
Lots of winders will make whatever you want. You can spec *anything*

with some of them. Like the Rutles said: All you need is cash.



If you will buy enough of them that is somewhat true. I had one place
that does a lot of secure sonar work offer to make me some MC240
outputs-but they wanted a quantity 1000 order. I replied that I dodn't
think they had ever made 1000 of anything in the last 40 years.

Their reply? "We haven't. But you aren't going to call us up five
years from now and demand one more at a 5X rush charge, and the Navy
will. For you, it's a thousand or none".


This is called "contractor spoilage". Any small to medium business
doing enough business with Uncle Sugar gets that way, and when Uncle
cuts them off, the bloated management fires everyone and goes home
having made all the money they wanted.

  #12   Report Post  
Patrick Turner
 
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Default



Accessory Section 8 wrote:

Bret Ludwig wrote:
Lots of winders will make whatever you want. You can spec *anything*

with some of them. Like the Rutles said: All you need is cash.



If you will buy enough of them that is somewhat true. I had one place
that does a lot of secure sonar work offer to make me some MC240
outputs-but they wanted a quantity 1000 order. I replied that I dodn't
think they had ever made 1000 of anything in the last 40 years.

Their reply? "We haven't. But you aren't going to call us up five
years from now and demand one more at a 5X rush charge, and the Navy
will. For you, it's a thousand or none".


This is called "contractor spoilage". Any small to medium business
doing enough business with Uncle Sugar gets that way, and when Uncle
cuts them off, the bloated management fires everyone and goes home
having made all the money they wanted.


The US ppl want to watch out that their govt does not sell everything off to
private
enterprise.
I saw a film recently called 'The Take' about the factory workers in
Argentina
who recently have ex-appropriated many factories after the ruination caused
by
Menen when he was in charge.

Its a different situation to the US, but there is ovewhelming global
pressure
for all businesses which make anything for anyone to just give up and leave
it to the chinese.

Anyway in Argentina the workers stole the closed down factories ( to keep
making the same good old tractors,
clothing, and ceramic tiles et all. )

Its amazing how productivity and profitability rises once you sack the
fukkin bosses
and the middle men and stop paying shareholders, none of whom know what a
day's real work is.
One reason private enterprize goes phut is the crippling
payments to the bosses for their BMW and their big lifestyles.

I don't know of any transformer winders in Argentina though....

Patrick Turner.



  #13   Report Post  
Andy Evans
 
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I'm building a PP 2a3 amp right now and haven't decided on the input
stage. I'd like to use 6J5G and/or 1626 valves. Open to other
suggestions, but like to keep to octal or UX5 types (I also have 76,
37, 56, 27). I'd also need a differential first stage for the option of
balanced or SE, and I have CCSs. 2a3 needs about -50v of bias. Ideas?
ANdy

  #14   Report Post  
Patrick Turner
 
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Andy Evans wrote:

I'm building a PP 2a3 amp right now and haven't decided on the input
stage. I'd like to use 6J5G and/or 1626 valves. Open to other
suggestions, but like to keep to octal or UX5 types (I also have 76,
37, 56, 27). I'd also need a differential first stage for the option of
balanced or SE, and I have CCSs. 2a3 needs about -50v of bias. Ideas?
ANdy


There must be 100 different ways to drive a pair of 2A3 in PP.
You will need around 37Vrms applied to each grid so the drive amp
should have ability for 70Vrms if possible.
To do that with an LTP using a pair of 6J5 is OK, and the input
stage/driver amp
that is shown at the 50/50 amp details below could be used.
http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm
I used 6CG7 = 6SN7 = 2 x 6J5.

Some folks would buy a decent IST and simply use a 6V6 or EL34 in triode
to drive the primary
and use the 1:2 step up to drive the 2A3 grids directly, with each 1/2
secondary
taken to separate low R value bias pots.
But if its mainly class A then cathode biasing is OK, and the IDST sec set
up as a
grounded CT winding.

With RL = 4k a-a, and a sec load of 4 ohms, and with Ea = 350V, Ia = 40mA,

PO = nearly 20 watts AB with a few watts of class A.
With 8ka-a to 8 ohms, PO = 15 watts, nearly all class A.

Rout will be about 2 ohms including tranny winding losses
and without global NFB.

Patrick Turner.




  #15   Report Post  
Sander deWaal
 
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"Andy Evans" said:

I'm building a PP 2a3 amp right now and haven't decided on the input
stage. I'd like to use 6J5G and/or 1626 valves. Open to other
suggestions, but like to keep to octal or UX5 types (I also have 76,
37, 56, 27). I'd also need a differential first stage for the option of
balanced or SE, and I have CCSs. 2a3 needs about -50v of bias. Ideas?
ANdy


In my 2A3 PPamp, I use a 6SN7 as input amplifier/cathodyne, followed
by a 6SN7 driver in common cathode.
Supply voltage for the driver and PI stages is ca. 350V, derived from
a separate winding on the transformer.
The output stage gets about 300V with a 5 k Raa transformer.
Atthe output, I get about 13 watts @ 1 %, mostly third order
(obviously!).
This is without GNFB, I added about 6 dB of that, which makes the
distortion about 0.5 %.

I know, I could at least skip one stage and get rid of 1 or 2 coupling
caps, but this sounds very good to me already.
Maybe in a future upgrade I'll use a LTP with CCS in the cathode path.

--

"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005


  #16   Report Post  
Fabio Berutti
 
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A well-known manufacturer of 400W amps like Mr. Turner is someone to trust,
when he says that as low as 4W can still be enough, if all the "sound" chain
is properly set. I treasure my own 2A3, particularly for its "effortless"
sound, which is not "weak" or "tubey" indeed. The only limit of the 2A3 SE
is "loud" music: my LS are about 97 dB, but when listening the Stones, well,
Mick simply isn't shouting and Keith's guitar isn't as mean and nasty as it
should.
Nevertheless, this is not a real limit: a HiFi set is a sort of a musical
instrument. Just like a Stratocaster is not considered "bad" 'cause it's
not suited for playing Bach, a 2A3 SE is not "bad" 'cause it's not good for
AC/DC (the Oz group, not the power supply); mr Turner correctly quoted that
the amp was very good for playing chamber music, not trash metal. In fact,
I agree with Mr. DeWaal: a 2A3 PP (or a 6B4G) is probably the closest thing
to the "perfect" sound: DHT, relatively low driving requirements, relatively
low output impedance (3K5 typ), reasonable B+, and an output power of about
10-12W which is enough even for the 9th symphony's chorus or the beginning
of "Back in black"... if You have efficient boxes and your neighbors are not
deaf.
There are thousands of "viable" circuits, but I'm still persuaded that from
an engineering point it's better to avoid problems (or distortion) than to
create some and then try to get rid of them. The 2A3 provides a nearly
perfect transfer function of its own, therefore the "tinkering" required to
make it "20 to 20k" can be kept to a minimum, which ultimately results in no
unpredictable "electronic traps", fixing some bug here just to make a worse
one somewhere else.

The only problem with a 2A3SE with good LSs is that suddenly You really hear
how badly many CDs are recorded. Some jazz LPs from the Fifties are lots
better.

Ciao

Fabio



"Patrick Turner" ha scritto nel messaggio
...
I finally have hooked up the stereo amp which uses 2A3
to my speakers which are about 90dB sensitivity.
I find I could listen all day and night to this underpowered
amplifier.
Whatever its doing it is doing it RIGHT.

The conditions are as follows.

Power tranny is Hammond type 370FX, and with
a 240V: 2 x 2.5V filament tranny.
Hammond 10H choke used with a quad of Sonic Frontier
PS caps of 1,100 uF each, so that with seriesed caps
I have 550uF, 10H, 550uF, as the CLC to supply power to the
pair of amp channels.
Rectifiers are IN5408 SS diodes. I don't strictly believe in tube
rectifiers;
I like them, I even use them sometimes; I just don't think they are
indispensible.
But in this case the use of a tube rectifier would have reduced the
available B+
and forced me to use fixed bias, which I don't like for any SE amps.

No need to dual mono power supplies.
180uF used to further filter the input and driver stages.


Output tubes are 2A3, RCA, NOS?, maybe used, not sure.
Ea = +270V, Ia = 57mA, cathode bias with 820ohms
bypassed with good quality 100V x 470uF.
heaters are AC 2.5V with a pot for hum nulling.

OPT is a 2.5k : 4/8/16 Hammond 25 watt rated SET gapped OPT
type 1627SE.

OPT is set up to match 2.5k to 4ohms, but I find 5 ohms is the most
correct load.

At 4Watts I get excellent open loop BW with this OPT
and freedom from saturation, of which there is only a slight trace at
about
7 Hz.

The OPT has queer resonances above 30kHz, makinf the use of
global NFB difficult for ppl with no clue about how to overcome such
connundrums.
It must be due to primary being wound close to the secondary,
and the absence of enough interleavings of windings, and the absence of
sufficient
insulation thickness.
Nevertheless, the 1627SE did turn out to be very usable, and sound is
glorious.

Driver tube is an ancient Radiotron 'made in australia' 6SN7,
used but OK. 1k Rk bypassed with 470uF, RL = 34k, 0.47 uF Wima coupling
cap,
150k grid bias R for 2A3, 1.8k series grid stopper.

The 6SN7 is operating fairly linearly and comfortably.
Without Ck bypass, the driver thd reduces, but then overall thd rises
a lot since less even order Dn cancelation takes place.

The fully bypassed Rk on the 6SN7 gives lowish Ra of about 5k for the
paralleled tube
and is thus a sufficiently low enough drive resistance to enhance the
micro detail behaviour of the
2A3, ( very necessary imho to get the best out of not just a triode
output tube,
but ALL output tubes.)

The input tube is 1/2 a 12AU7 of unknown lineage; it measured nicely,
and I like the 12AU7 for inputs; its warm, accurate, and sounds
glorious.

Its Rk is 1.8k, and also bypassed with 470uF, and taken then to 100 ohms
for
the global NFB to be applied.
RL is 50k, 0.47uF to a network for LF gain stepping, 1M+0.033uF
plus 220k, typical in many of my amps to vastly
improve the bass stability when the 12dB of global FB is applied.

The FB resistor divider network is 750 ohms to 100 ohms
with a phase tweaker bypass cap across the 750 ohms = 1,000 pF.
There is a 470pF plus 2.7k zobel network connected from the
driver grid to 0V to control the HF gain and ultimate phase shift of the

12AU7 to 6SN7 interface.
A further 5.6ohms+0.47uF Zobel network is across the OPT secondary,
and finally I got the amp to be fairly ring free when connected to
any value of cap without a pure R load, and when using a square wave.
Open loop BW with all compensation zobels in place was 20Hz to 20kHz,
-3dB,
and with 12 dB of FB the full power BW is 5Hz to 55kHz, 5 ohms.
It remains the same at lower levels of power.

A 5 kHz square wave is a bit ragged due to the mentioned OPT design
simplicity,
but the sine wave response between 30Hz and 20hHz right up to clipping
is dead flat.

A 50k Alps Black pot is used for the gain control.

Input sensitivity with 12dB applied global NFB is 0.7Vrms.
The amp's use with an CD player is fine.
Just no need for any preamp.

The sound is that of a far more powerful amplifier,
with tremendous sense of rightness, instrument detail, warmth without
muddle, not the slightest hint of any lack of bass, the usual beautiful
mids, and detailed top end.

The amp measures well at less than 1% thd at 4 watts into 5 ohms,
mainly all 2H.
But at normal levels of a watt the 3H and other H are present below the
2H
which can be seen on the CRO when monitoring the THD at all levels.
Ro is 0.47 ohm, and although my speakers vary between
4 and 20ohms, the sound appears firm, well timbred, and there isn't any
hint
of the sound being that from an inadequate amplifier.

I played Handel's water music, the sound track of 'The Pianist' for my
tests plus
a not so wonderful Naxos CD, 'The Best of Bach'.

Who says SET amps suck?

Certainly not I!.

Methinks that if the owner wanted more power, he could simply swap the
2A3 for a KT90 since the PT has a 6.3V heater winding, and then
remove the series R I have placed in the B+ lines to trim the B+
to where I want it, and with 270V, and with the UL tap on the
OPT that is provided, maybe 9+ watts of SEUL would be available.

The now unused 1670 OPT UL tap is at 40%.
But it could be at 60%, if you use the plate winding reversed,
thus further drifting a tetrode towards triode, but still not
suffering a huge loss of power due to grid current limitations.

300B could also be used, and with slightly more Ia,
but with the same low Ea, thus suiting moderate power and good matching
to
low value loads, which is a major failing in many SET amps;
they try to match so max power is at 8ohms, but that is
nearly always wrong with modern speakers, and
max power should occur at 3 or 4 ohms.


Patrick Turner.






  #17   Report Post  
Fabio Berutti
 
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A 2A3 PP will be a great unit in any case. The 6J5 (or its close relative
6C5) is a great tube, but it would be simpler to use 6SN7s. Personally, I
prefer "long tailed" phase splitters to cathodynes, don't know why but they
sound more "vivid". Suppose You place a 6SN7 at the entrance as a diff amp,
then another one as a LT phase splitter and driver. Using the 2A3 in PP,
with cathode bias, You'll need a 350V B+, which is high enough to get the
required voltage swing out of the long-tail pair. If You don't mind using 4
tubes, the 6J5s can be matched to minimise distortion (it's difficult to
find 2 similar triodes in the same glass envelope, therefore diff amps with
6SN7s could show some minor unbalance).
The diff amp at the 1st stage will provide a feedback entry too.
As per the output transformer, any good 3k5 unit will fit. BTW, being a PP
unit, it can be fed AC to the filaments, no problems. I'd keep separate
windings for each tube in order to have each one individually biased; this
allows to use any tube and it is safer in case of sudden failure of one
tube, but it is obviously easier and cheaper to have the 2 tubes of the PP
pair fed by a single transformer winding, having a center tap referred to
ground by the common cathode bias resistor (+capacitor). In this case, in
order to match quiescent current, tubes shall be matched on a good tester
(or bought from a dependable source as matched pairs),

Let us know..

Ciao

Fabio



"Andy Evans" ha scritto nel messaggio
oups.com...
I'm building a PP 2a3 amp right now and haven't decided on the input
stage. I'd like to use 6J5G and/or 1626 valves. Open to other
suggestions, but like to keep to octal or UX5 types (I also have 76,
37, 56, 27). I'd also need a differential first stage for the option of
balanced or SE, and I have CCSs. 2a3 needs about -50v of bias. Ideas?
ANdy



  #18   Report Post  
Patrick Turner
 
Posts: n/a
Default



Fabio Berutti wrote:

A well-known manufacturer of 400W amps like Mr. Turner is someone to trust,
when he says that as low as 4W can still be enough, if all the "sound" chain
is properly set. I treasure my own 2A3, particularly for its "effortless"
sound, which is not "weak" or "tubey" indeed. The only limit of the 2A3 SE
is "loud" music: my LS are about 97 dB, but when listening the Stones, well,
Mick simply isn't shouting and Keith's guitar isn't as mean and nasty as it
should.
Nevertheless, this is not a real limit: a HiFi set is a sort of a musical
instrument. Just like a Stratocaster is not considered "bad" 'cause it's
not suited for playing Bach, a 2A3 SE is not "bad" 'cause it's not good for
AC/DC (the Oz group, not the power supply); mr Turner correctly quoted that
the amp was very good for playing chamber music, not trash metal. In fact,
I agree with Mr. DeWaal: a 2A3 PP (or a 6B4G) is probably the closest thing
to the "perfect" sound: DHT, relatively low driving requirements, relatively
low output impedance (3K5 typ), reasonable B+, and an output power of about
10-12W which is enough even for the 9th symphony's chorus or the beginning
of "Back in black"... if You have efficient boxes and your neighbors are not
deaf.
There are thousands of "viable" circuits, but I'm still persuaded that from
an engineering point it's better to avoid problems (or distortion) than to
create some and then try to get rid of them. The 2A3 provides a nearly
perfect transfer function of its own, therefore the "tinkering" required to
make it "20 to 20k" can be kept to a minimum, which ultimately results in no
unpredictable "electronic traps", fixing some bug here just to make a worse
one somewhere else.

The only problem with a 2A3SE with good LSs is that suddenly You really hear
how badly many CDs are recorded. Some jazz LPs from the Fifties are lots
better.

Ciao

Fabio


You are dead right about the LPs from bygone days.

And the guy who had me prepare the 2A3 amps for his horn system
has also aquired a pair of Tannoy monitor gold dual concentrics, about 96dB/W/M.

The Tannoys will run fine on 4 watts.

But a guy here says the 2A3 is a boogie tube; for
something to tug the heart strings i should listen with a 45.

My speakers are fairly insensitive, so I like a few more watts myself,
I would get by with 8 watts from a 300B, but 25 watts
would be nicer, mainly because the power is all from the sweet zone of the first

few watts.

300 watts per channel is OK for the guy with speakers of only
80 dB/W/M, or who has tolerant neighbours, and is young enough not
to mind loud sound, or who is more fanatical about the power being from an amp's
sweet zone.
A dozen 6550 do have a large pure class A power region.

Patrick Turner




"Patrick Turner" ha scritto nel messaggio
...
I finally have hooked up the stereo amp which uses 2A3
to my speakers which are about 90dB sensitivity.
I find I could listen all day and night to this underpowered
amplifier.
Whatever its doing it is doing it RIGHT.

The conditions are as follows.

Power tranny is Hammond type 370FX, and with
a 240V: 2 x 2.5V filament tranny.
Hammond 10H choke used with a quad of Sonic Frontier
PS caps of 1,100 uF each, so that with seriesed caps
I have 550uF, 10H, 550uF, as the CLC to supply power to the
pair of amp channels.
Rectifiers are IN5408 SS diodes. I don't strictly believe in tube
rectifiers;
I like them, I even use them sometimes; I just don't think they are
indispensible.
But in this case the use of a tube rectifier would have reduced the
available B+
and forced me to use fixed bias, which I don't like for any SE amps.

No need to dual mono power supplies.
180uF used to further filter the input and driver stages.


Output tubes are 2A3, RCA, NOS?, maybe used, not sure.
Ea = +270V, Ia = 57mA, cathode bias with 820ohms
bypassed with good quality 100V x 470uF.
heaters are AC 2.5V with a pot for hum nulling.

OPT is a 2.5k : 4/8/16 Hammond 25 watt rated SET gapped OPT
type 1627SE.

OPT is set up to match 2.5k to 4ohms, but I find 5 ohms is the most
correct load.

At 4Watts I get excellent open loop BW with this OPT
and freedom from saturation, of which there is only a slight trace at
about
7 Hz.

The OPT has queer resonances above 30kHz, makinf the use of
global NFB difficult for ppl with no clue about how to overcome such
connundrums.
It must be due to primary being wound close to the secondary,
and the absence of enough interleavings of windings, and the absence of
sufficient
insulation thickness.
Nevertheless, the 1627SE did turn out to be very usable, and sound is
glorious.

Driver tube is an ancient Radiotron 'made in australia' 6SN7,
used but OK. 1k Rk bypassed with 470uF, RL = 34k, 0.47 uF Wima coupling
cap,
150k grid bias R for 2A3, 1.8k series grid stopper.

The 6SN7 is operating fairly linearly and comfortably.
Without Ck bypass, the driver thd reduces, but then overall thd rises
a lot since less even order Dn cancelation takes place.

The fully bypassed Rk on the 6SN7 gives lowish Ra of about 5k for the
paralleled tube
and is thus a sufficiently low enough drive resistance to enhance the
micro detail behaviour of the
2A3, ( very necessary imho to get the best out of not just a triode
output tube,
but ALL output tubes.)

The input tube is 1/2 a 12AU7 of unknown lineage; it measured nicely,
and I like the 12AU7 for inputs; its warm, accurate, and sounds
glorious.

Its Rk is 1.8k, and also bypassed with 470uF, and taken then to 100 ohms
for
the global NFB to be applied.
RL is 50k, 0.47uF to a network for LF gain stepping, 1M+0.033uF
plus 220k, typical in many of my amps to vastly
improve the bass stability when the 12dB of global FB is applied.

The FB resistor divider network is 750 ohms to 100 ohms
with a phase tweaker bypass cap across the 750 ohms = 1,000 pF.
There is a 470pF plus 2.7k zobel network connected from the
driver grid to 0V to control the HF gain and ultimate phase shift of the

12AU7 to 6SN7 interface.
A further 5.6ohms+0.47uF Zobel network is across the OPT secondary,
and finally I got the amp to be fairly ring free when connected to
any value of cap without a pure R load, and when using a square wave.
Open loop BW with all compensation zobels in place was 20Hz to 20kHz,
-3dB,
and with 12 dB of FB the full power BW is 5Hz to 55kHz, 5 ohms.
It remains the same at lower levels of power.

A 5 kHz square wave is a bit ragged due to the mentioned OPT design
simplicity,
but the sine wave response between 30Hz and 20hHz right up to clipping
is dead flat.

A 50k Alps Black pot is used for the gain control.

Input sensitivity with 12dB applied global NFB is 0.7Vrms.
The amp's use with an CD player is fine.
Just no need for any preamp.

The sound is that of a far more powerful amplifier,
with tremendous sense of rightness, instrument detail, warmth without
muddle, not the slightest hint of any lack of bass, the usual beautiful
mids, and detailed top end.

The amp measures well at less than 1% thd at 4 watts into 5 ohms,
mainly all 2H.
But at normal levels of a watt the 3H and other H are present below the
2H
which can be seen on the CRO when monitoring the THD at all levels.
Ro is 0.47 ohm, and although my speakers vary between
4 and 20ohms, the sound appears firm, well timbred, and there isn't any
hint
of the sound being that from an inadequate amplifier.

I played Handel's water music, the sound track of 'The Pianist' for my
tests plus
a not so wonderful Naxos CD, 'The Best of Bach'.

Who says SET amps suck?

Certainly not I!.

Methinks that if the owner wanted more power, he could simply swap the
2A3 for a KT90 since the PT has a 6.3V heater winding, and then
remove the series R I have placed in the B+ lines to trim the B+
to where I want it, and with 270V, and with the UL tap on the
OPT that is provided, maybe 9+ watts of SEUL would be available.

The now unused 1670 OPT UL tap is at 40%.
But it could be at 60%, if you use the plate winding reversed,
thus further drifting a tetrode towards triode, but still not
suffering a huge loss of power due to grid current limitations.

300B could also be used, and with slightly more Ia,
but with the same low Ea, thus suiting moderate power and good matching
to
low value loads, which is a major failing in many SET amps;
they try to match so max power is at 8ohms, but that is
nearly always wrong with modern speakers, and
max power should occur at 3 or 4 ohms.


Patrick Turner.





  #19   Report Post  
Patrick Turner
 
Posts: n/a
Default



Fabio Berutti wrote:

A 2A3 PP will be a great unit in any case. The 6J5 (or its close relative
6C5) is a great tube, but it would be simpler to use 6SN7s. Personally, I
prefer "long tailed" phase splitters to cathodynes, don't know why but they
sound more "vivid". Suppose You place a 6SN7 at the entrance as a diff amp,
then another one as a LT phase splitter and driver. Using the 2A3 in PP,
with cathode bias, You'll need a 350V B+, which is high enough to get the
required voltage swing out of the long-tail pair. If You don't mind using 4
tubes, the 6J5s can be matched to minimise distortion (it's difficult to
find 2 similar triodes in the same glass envelope, therefore diff amps with
6SN7s could show some minor unbalance).
The diff amp at the 1st stage will provide a feedback entry too.
As per the output transformer, any good 3k5 unit will fit. BTW, being a PP
unit, it can be fed AC to the filaments, no problems. I'd keep separate
windings for each tube in order to have each one individually biased; this
allows to use any tube and it is safer in case of sudden failure of one
tube, but it is obviously easier and cheaper to have the 2 tubes of the PP
pair fed by a single transformer winding, having a center tap referred to
ground by the common cathode bias resistor (+capacitor). In this case, in
order to match quiescent current, tubes shall be matched on a good tester
(or bought from a dependable source as matched pairs),

Let us know..

Ciao

Fabio


The standard Williamson circuit is fine for PP2A3
instead of KT66.
The concertina inverter only has to produce a small voltage to drive the
balanced amp.

But I like the slightly simpler SET input + LTP driver.

Patrick Turner.



"Andy Evans" ha scritto nel messaggio
oups.com...
I'm building a PP 2a3 amp right now and haven't decided on the input
stage. I'd like to use 6J5G and/or 1626 valves. Open to other
suggestions, but like to keep to octal or UX5 types (I also have 76,
37, 56, 27). I'd also need a differential first stage for the option of
balanced or SE, and I have CCSs. 2a3 needs about -50v of bias. Ideas?
ANdy


  #20   Report Post  
Bret Ludwig
 
Posts: n/a
Default

A big early tube guru was a guy named Bob Fulton in the US. He had
some bizarre ideas, one of which was there were only three good power
tubes, the 10, the 45 and the 845. He still has his followers.



  #21   Report Post  
Andre Jute
 
Posts: n/a
Default

Definitely.

One of the finest amps I ever heard was a PP 2A3 from the late lamented
Audio Innovations called IIRC The First.

In Patrick's application SE 2A3 will be more than adequately powerful
to drive the HF, which really doesn't require even a whole watt even on
orchestral fortes. (Experiment: make a filter to lose everything below
8K5Hz. Listen to the remainder. It is a sort of buzz, not music. Its
actual power content is fractional. Most people a lot younger than the
average age of RATs cannot hear that there is a difference between one
of my Impresarion with the tweeter and one without, the one without
tapering off about 10kHz.)

But I have my doubts about SE 2A3 even with a sensitive fullrange horn.
A DHT is usually decently silent but I like further to silence it with
a high load on the plate. When you do that the power falls alarmingly,
soon to under one watt, which is not too hot on even a Lowther horn if
you want to play orchestral music. With a Lowther horn (c100dB/w/m) I
like about 4W of very silent power, which is why I use 300B instead of
2A3. To address Fabio's remarks, I don't think a 3.5W 2A3 SE with a
97dB speaker is a rock'n'roll combination. Far too much powere required
in those bass "transients" which is rock'n'roll can go on forever.

Also, while theoretically I like the *concept* of PP DHT, I am a
Calvinist who shrinks from such expense when a triode-linked PP EL34
amp will give you the same power and 99 per cent of the sound for half
the price. There used to be a salesman called Zip on RAO (he was
disgraced when he couldn't distinguish one cable from another); Zip
used to tell people who complained about the price of the amps he sold
that they lacked commitment to their music, as if how much you spend is
a mark of merit. Zip was full of ****. I have passion for my music but
there is no reason to let it interfere with common sense.

Andre Jute
Gotta sleep. E&OE.

Fabio Berutti wrote:
A well-known manufacturer of 400W amps like Mr. Turner is someone to trust,
when he says that as low as 4W can still be enough, if all the "sound" chain
is properly set. I treasure my own 2A3, particularly for its "effortless"
sound, which is not "weak" or "tubey" indeed. The only limit of the 2A3 SE
is "loud" music: my LS are about 97 dB, but when listening the Stones, well,
Mick simply isn't shouting and Keith's guitar isn't as mean and nasty as it
should.
Nevertheless, this is not a real limit: a HiFi set is a sort of a musical
instrument. Just like a Stratocaster is not considered "bad" 'cause it's
not suited for playing Bach, a 2A3 SE is not "bad" 'cause it's not good for
AC/DC (the Oz group, not the power supply); mr Turner correctly quoted that
the amp was very good for playing chamber music, not trash metal. In fact,
I agree with Mr. DeWaal: a 2A3 PP (or a 6B4G) is probably the closest thing
to the "perfect" sound: DHT, relatively low driving requirements, relatively
low output impedance (3K5 typ), reasonable B+, and an output power of about
10-12W which is enough even for the 9th symphony's chorus or the beginning
of "Back in black"... if You have efficient boxes and your neighbors are not
deaf.
There are thousands of "viable" circuits, but I'm still persuaded that from
an engineering point it's better to avoid problems (or distortion) than to
create some and then try to get rid of them. The 2A3 provides a nearly
perfect transfer function of its own, therefore the "tinkering" required to
make it "20 to 20k" can be kept to a minimum, which ultimately results in no
unpredictable "electronic traps", fixing some bug here just to make a worse
one somewhere else.

The only problem with a 2A3SE with good LSs is that suddenly You really hear
how badly many CDs are recorded. Some jazz LPs from the Fifties are lots
better.

Ciao

Fabio



"Patrick Turner" ha scritto nel messaggio
...
I finally have hooked up the stereo amp which uses 2A3
to my speakers which are about 90dB sensitivity.
I find I could listen all day and night to this underpowered
amplifier.
Whatever its doing it is doing it RIGHT.

The conditions are as follows.

Power tranny is Hammond type 370FX, and with
a 240V: 2 x 2.5V filament tranny.
Hammond 10H choke used with a quad of Sonic Frontier
PS caps of 1,100 uF each, so that with seriesed caps
I have 550uF, 10H, 550uF, as the CLC to supply power to the
pair of amp channels.
Rectifiers are IN5408 SS diodes. I don't strictly believe in tube
rectifiers;
I like them, I even use them sometimes; I just don't think they are
indispensible.
But in this case the use of a tube rectifier would have reduced the
available B+
and forced me to use fixed bias, which I don't like for any SE amps.

No need to dual mono power supplies.
180uF used to further filter the input and driver stages.


Output tubes are 2A3, RCA, NOS?, maybe used, not sure.
Ea = +270V, Ia = 57mA, cathode bias with 820ohms
bypassed with good quality 100V x 470uF.
heaters are AC 2.5V with a pot for hum nulling.

OPT is a 2.5k : 4/8/16 Hammond 25 watt rated SET gapped OPT
type 1627SE.

OPT is set up to match 2.5k to 4ohms, but I find 5 ohms is the most
correct load.

At 4Watts I get excellent open loop BW with this OPT
and freedom from saturation, of which there is only a slight trace at
about
7 Hz.

The OPT has queer resonances above 30kHz, makinf the use of
global NFB difficult for ppl with no clue about how to overcome such
connundrums.
It must be due to primary being wound close to the secondary,
and the absence of enough interleavings of windings, and the absence of
sufficient
insulation thickness.
Nevertheless, the 1627SE did turn out to be very usable, and sound is
glorious.

Driver tube is an ancient Radiotron 'made in australia' 6SN7,
used but OK. 1k Rk bypassed with 470uF, RL = 34k, 0.47 uF Wima coupling
cap,
150k grid bias R for 2A3, 1.8k series grid stopper.

The 6SN7 is operating fairly linearly and comfortably.
Without Ck bypass, the driver thd reduces, but then overall thd rises
a lot since less even order Dn cancelation takes place.

The fully bypassed Rk on the 6SN7 gives lowish Ra of about 5k for the
paralleled tube
and is thus a sufficiently low enough drive resistance to enhance the
micro detail behaviour of the
2A3, ( very necessary imho to get the best out of not just a triode
output tube,
but ALL output tubes.)

The input tube is 1/2 a 12AU7 of unknown lineage; it measured nicely,
and I like the 12AU7 for inputs; its warm, accurate, and sounds
glorious.

Its Rk is 1.8k, and also bypassed with 470uF, and taken then to 100 ohms
for
the global NFB to be applied.
RL is 50k, 0.47uF to a network for LF gain stepping, 1M+0.033uF
plus 220k, typical in many of my amps to vastly
improve the bass stability when the 12dB of global FB is applied.

The FB resistor divider network is 750 ohms to 100 ohms
with a phase tweaker bypass cap across the 750 ohms = 1,000 pF.
There is a 470pF plus 2.7k zobel network connected from the
driver grid to 0V to control the HF gain and ultimate phase shift of the

12AU7 to 6SN7 interface.
A further 5.6ohms+0.47uF Zobel network is across the OPT secondary,
and finally I got the amp to be fairly ring free when connected to
any value of cap without a pure R load, and when using a square wave.
Open loop BW with all compensation zobels in place was 20Hz to 20kHz,
-3dB,
and with 12 dB of FB the full power BW is 5Hz to 55kHz, 5 ohms.
It remains the same at lower levels of power.

A 5 kHz square wave is a bit ragged due to the mentioned OPT design
simplicity,
but the sine wave response between 30Hz and 20hHz right up to clipping
is dead flat.

A 50k Alps Black pot is used for the gain control.

Input sensitivity with 12dB applied global NFB is 0.7Vrms.
The amp's use with an CD player is fine.
Just no need for any preamp.

The sound is that of a far more powerful amplifier,
with tremendous sense of rightness, instrument detail, warmth without
muddle, not the slightest hint of any lack of bass, the usual beautiful
mids, and detailed top end.

The amp measures well at less than 1% thd at 4 watts into 5 ohms,
mainly all 2H.
But at normal levels of a watt the 3H and other H are present below the
2H
which can be seen on the CRO when monitoring the THD at all levels.
Ro is 0.47 ohm, and although my speakers vary between
4 and 20ohms, the sound appears firm, well timbred, and there isn't any
hint
of the sound being that from an inadequate amplifier.

I played Handel's water music, the sound track of 'The Pianist' for my
tests plus
a not so wonderful Naxos CD, 'The Best of Bach'.

Who says SET amps suck?

Certainly not I!.

Methinks that if the owner wanted more power, he could simply swap the
2A3 for a KT90 since the PT has a 6.3V heater winding, and then
remove the series R I have placed in the B+ lines to trim the B+
to where I want it, and with 270V, and with the UL tap on the
OPT that is provided, maybe 9+ watts of SEUL would be available.

The now unused 1670 OPT UL tap is at 40%.
But it could be at 60%, if you use the plate winding reversed,
thus further drifting a tetrode towards triode, but still not
suffering a huge loss of power due to grid current limitations.

300B could also be used, and with slightly more Ia,
but with the same low Ea, thus suiting moderate power and good matching
to
low value loads, which is a major failing in many SET amps;
they try to match so max power is at 8ohms, but that is
nearly always wrong with modern speakers, and
max power should occur at 3 or 4 ohms.


Patrick Turner.





  #22   Report Post  
VinylBigot
 
Posts: n/a
Default

Absolutely agree. I've gone through the whole gambit of PP tube amps of all
power sizes, moved on to SET's and settled on the 2A3 as having the most
truly beautiful and natural sound. I wrote a piece on a few forums asking
for other opinions, and most agreed that the 2A3 won out over 300B and 45.
I felt that the 45 gave a percieved "cleaner" sound, but it was almost
clinical--and not natural. I like a sound that is as close to a classical
live concert in a good hall, as possible. There is a fair amount of
reflection which colors the sound in a live concert--the 2A3's seem to do a
very good job of mimicking this. I also found that the supposed improvement
from cobalt OPT's was not to my liking either.

I've gone through a whole set of 2A3's NOS to find the best. My favorite is
a pair of no-name RadTel's from the 30's. Next is RCA silver, and then
National Union, then RCA black. The SovTeks and ValveArt's just plain
stink.

I use Lowthers which gives plently of volume in my listening room. Even a
71A amp has enough power for me.

"Patrick Turner" wrote in message
...
I finally have hooked up the stereo amp which uses 2A3
to my speakers which are about 90dB sensitivity.
I find I could listen all day and night to this underpowered
amplifier.
Whatever its doing it is doing it RIGHT.

The conditions are as follows.

Power tranny is Hammond type 370FX, and with
a 240V: 2 x 2.5V filament tranny.
Hammond 10H choke used with a quad of Sonic Frontier
PS caps of 1,100 uF each, so that with seriesed caps
I have 550uF, 10H, 550uF, as the CLC to supply power to the
pair of amp channels.
Rectifiers are IN5408 SS diodes. I don't strictly believe in tube
rectifiers;
I like them, I even use them sometimes; I just don't think they are
indispensible.
But in this case the use of a tube rectifier would have reduced the
available B+
and forced me to use fixed bias, which I don't like for any SE amps.

No need to dual mono power supplies.
180uF used to further filter the input and driver stages.


Output tubes are 2A3, RCA, NOS?, maybe used, not sure.
Ea = +270V, Ia = 57mA, cathode bias with 820ohms
bypassed with good quality 100V x 470uF.
heaters are AC 2.5V with a pot for hum nulling.

OPT is a 2.5k : 4/8/16 Hammond 25 watt rated SET gapped OPT
type 1627SE.

OPT is set up to match 2.5k to 4ohms, but I find 5 ohms is the most
correct load.

At 4Watts I get excellent open loop BW with this OPT
and freedom from saturation, of which there is only a slight trace at
about
7 Hz.

The OPT has queer resonances above 30kHz, makinf the use of
global NFB difficult for ppl with no clue about how to overcome such
connundrums.
It must be due to primary being wound close to the secondary,
and the absence of enough interleavings of windings, and the absence of
sufficient
insulation thickness.
Nevertheless, the 1627SE did turn out to be very usable, and sound is
glorious.

Driver tube is an ancient Radiotron 'made in australia' 6SN7,
used but OK. 1k Rk bypassed with 470uF, RL = 34k, 0.47 uF Wima coupling
cap,
150k grid bias R for 2A3, 1.8k series grid stopper.

The 6SN7 is operating fairly linearly and comfortably.
Without Ck bypass, the driver thd reduces, but then overall thd rises
a lot since less even order Dn cancelation takes place.

The fully bypassed Rk on the 6SN7 gives lowish Ra of about 5k for the
paralleled tube
and is thus a sufficiently low enough drive resistance to enhance the
micro detail behaviour of the
2A3, ( very necessary imho to get the best out of not just a triode
output tube,
but ALL output tubes.)

The input tube is 1/2 a 12AU7 of unknown lineage; it measured nicely,
and I like the 12AU7 for inputs; its warm, accurate, and sounds
glorious.

Its Rk is 1.8k, and also bypassed with 470uF, and taken then to 100 ohms
for
the global NFB to be applied.
RL is 50k, 0.47uF to a network for LF gain stepping, 1M+0.033uF
plus 220k, typical in many of my amps to vastly
improve the bass stability when the 12dB of global FB is applied.

The FB resistor divider network is 750 ohms to 100 ohms
with a phase tweaker bypass cap across the 750 ohms = 1,000 pF.
There is a 470pF plus 2.7k zobel network connected from the
driver grid to 0V to control the HF gain and ultimate phase shift of the

12AU7 to 6SN7 interface.
A further 5.6ohms+0.47uF Zobel network is across the OPT secondary,
and finally I got the amp to be fairly ring free when connected to
any value of cap without a pure R load, and when using a square wave.
Open loop BW with all compensation zobels in place was 20Hz to 20kHz,
-3dB,
and with 12 dB of FB the full power BW is 5Hz to 55kHz, 5 ohms.
It remains the same at lower levels of power.

A 5 kHz square wave is a bit ragged due to the mentioned OPT design
simplicity,
but the sine wave response between 30Hz and 20hHz right up to clipping
is dead flat.

A 50k Alps Black pot is used for the gain control.

Input sensitivity with 12dB applied global NFB is 0.7Vrms.
The amp's use with an CD player is fine.
Just no need for any preamp.

The sound is that of a far more powerful amplifier,
with tremendous sense of rightness, instrument detail, warmth without
muddle, not the slightest hint of any lack of bass, the usual beautiful
mids, and detailed top end.

The amp measures well at less than 1% thd at 4 watts into 5 ohms,
mainly all 2H.
But at normal levels of a watt the 3H and other H are present below the
2H
which can be seen on the CRO when monitoring the THD at all levels.
Ro is 0.47 ohm, and although my speakers vary between
4 and 20ohms, the sound appears firm, well timbred, and there isn't any
hint
of the sound being that from an inadequate amplifier.

I played Handel's water music, the sound track of 'The Pianist' for my
tests plus
a not so wonderful Naxos CD, 'The Best of Bach'.

Who says SET amps suck?

Certainly not I!.

Methinks that if the owner wanted more power, he could simply swap the
2A3 for a KT90 since the PT has a 6.3V heater winding, and then
remove the series R I have placed in the B+ lines to trim the B+
to where I want it, and with 270V, and with the UL tap on the
OPT that is provided, maybe 9+ watts of SEUL would be available.

The now unused 1670 OPT UL tap is at 40%.
But it could be at 60%, if you use the plate winding reversed,
thus further drifting a tetrode towards triode, but still not
suffering a huge loss of power due to grid current limitations.

300B could also be used, and with slightly more Ia,
but with the same low Ea, thus suiting moderate power and good matching
to
low value loads, which is a major failing in many SET amps;
they try to match so max power is at 8ohms, but that is
nearly always wrong with modern speakers, and
max power should occur at 3 or 4 ohms.


Patrick Turner.






  #23   Report Post  
Fabio Berutti
 
Posts: n/a
Default


"Patrick Turner" ha scritto nel messaggio
...


Fabio Berutti wrote:

A well-known manufacturer of 400W amps like Mr. Turner is someone to
trust,
when he says that as low as 4W can still be enough, if all the "sound"
chain
is properly set. I treasure my own 2A3, particularly for its
"effortless"
sound, which is not "weak" or "tubey" indeed. The only limit of the 2A3
SE
is "loud" music: my LS are about 97 dB, but when listening the Stones,
well,
Mick simply isn't shouting and Keith's guitar isn't as mean and nasty as
it
should.
Nevertheless, this is not a real limit: a HiFi set is a sort of a musical
instrument. Just like a Stratocaster is not considered "bad" 'cause it's
not suited for playing Bach, a 2A3 SE is not "bad" 'cause it's not good
for
AC/DC (the Oz group, not the power supply); mr Turner correctly quoted
that
the amp was very good for playing chamber music, not trash metal. In
fact,
I agree with Mr. DeWaal: a 2A3 PP (or a 6B4G) is probably the closest
thing
to the "perfect" sound: DHT, relatively low driving requirements,
relatively
low output impedance (3K5 typ), reasonable B+, and an output power of
about
10-12W which is enough even for the 9th symphony's chorus or the
beginning
of "Back in black"... if You have efficient boxes and your neighbors are
not
deaf.
There are thousands of "viable" circuits, but I'm still persuaded that
from
an engineering point it's better to avoid problems (or distortion) than
to
create some and then try to get rid of them. The 2A3 provides a nearly
perfect transfer function of its own, therefore the "tinkering" required
to
make it "20 to 20k" can be kept to a minimum, which ultimately results in
no
unpredictable "electronic traps", fixing some bug here just to make a
worse
one somewhere else.

The only problem with a 2A3SE with good LSs is that suddenly You really
hear
how badly many CDs are recorded. Some jazz LPs from the Fifties are lots
better.

Ciao

Fabio


You are dead right about the LPs from bygone days.

And the guy who had me prepare the 2A3 amps for his horn system
has also aquired a pair of Tannoy monitor gold dual concentrics, about
96dB/W/M.

The Tannoys will run fine on 4 watts.


Indeed. This is a fine example of a well-balanced system, provided a good
CD or better phono preamp is provided.


But a guy here says the 2A3 is a boogie tube; for
something to tug the heart strings i should listen with a 45.


I'm working on a VT52 (or 45S) for a friend of mine right now. I know this
tube is said to be in the same league of TFK AD1 or Osram PX4, in terms of
"sonic purity", should it mean anything... but a scarce 2W is really a
measle power. Efficiency should be in the 100dB range to play Tchaikowsky's
1st concert with a good dynamic and "space", or it sounds like Snowhite
playing a toy piano in front of a dwarfs'orchestra.
My friend just moved to Geneva for work, and it seems that "loud" in
Switzerland has a peculiar meaning: at 75 dB the neighbors show up dressed
like Wilhelm Tell and try to kill You with 5kgs chocolate bars. Therefore,
the best he can get is 2 good watts.
From my point of view, a very weak amp poses a serious problem to the
loudspeakers, while an unefficient LS poses some problem to the amp.
Generally speaking it's easier to solve electronic problems than
electro-acoustic-mechanic ones, ie. it's easier to make a 100W amp which can
drive almost anything than to make a box which can provide good sound even
at 1W; this is why I wouldn't use anything smaller than the 2A3 unless there
are peculiar reasons like in this case. For people wanting extreme
solutions there's the 71A: an amazingly good sounding DHT, if You can make
it with 0.6W. I wouldn't use it for anything but an headphone amp. This
is why I think that a PP made with 2A3s or eq (6B4Gs or trioded 6L6 on the
cheap side...) is "the best", 'cos it's a sensible compromise: simple
circuitry and enough power to drive a "non extreme" LS.

Ciao

FB



My speakers are fairly insensitive, so I like a few more watts myself,
I would get by with 8 watts from a 300B, but 25 watts
would be nicer, mainly because the power is all from the sweet zone of the
first

few watts.

300 watts per channel is OK for the guy with speakers of only
80 dB/W/M, or who has tolerant neighbours, and is young enough not
to mind loud sound, or who is more fanatical about the power being from an
amp's
sweet zone.
A dozen 6550 do have a large pure class A power region.

Patrick Turner




"Patrick Turner" ha scritto nel messaggio
...
I finally have hooked up the stereo amp which uses 2A3
to my speakers which are about 90dB sensitivity.
I find I could listen all day and night to this underpowered
amplifier.
Whatever its doing it is doing it RIGHT.

The conditions are as follows.

Power tranny is Hammond type 370FX, and with
a 240V: 2 x 2.5V filament tranny.
Hammond 10H choke used with a quad of Sonic Frontier
PS caps of 1,100 uF each, so that with seriesed caps
I have 550uF, 10H, 550uF, as the CLC to supply power to the
pair of amp channels.
Rectifiers are IN5408 SS diodes. I don't strictly believe in tube
rectifiers;
I like them, I even use them sometimes; I just don't think they are
indispensible.
But in this case the use of a tube rectifier would have reduced the
available B+
and forced me to use fixed bias, which I don't like for any SE amps.

No need to dual mono power supplies.
180uF used to further filter the input and driver stages.


Output tubes are 2A3, RCA, NOS?, maybe used, not sure.
Ea = +270V, Ia = 57mA, cathode bias with 820ohms
bypassed with good quality 100V x 470uF.
heaters are AC 2.5V with a pot for hum nulling.

OPT is a 2.5k : 4/8/16 Hammond 25 watt rated SET gapped OPT
type 1627SE.

OPT is set up to match 2.5k to 4ohms, but I find 5 ohms is the most
correct load.

At 4Watts I get excellent open loop BW with this OPT
and freedom from saturation, of which there is only a slight trace at
about
7 Hz.

The OPT has queer resonances above 30kHz, makinf the use of
global NFB difficult for ppl with no clue about how to overcome such
connundrums.
It must be due to primary being wound close to the secondary,
and the absence of enough interleavings of windings, and the absence of
sufficient
insulation thickness.
Nevertheless, the 1627SE did turn out to be very usable, and sound is
glorious.

Driver tube is an ancient Radiotron 'made in australia' 6SN7,
used but OK. 1k Rk bypassed with 470uF, RL = 34k, 0.47 uF Wima
coupling
cap,
150k grid bias R for 2A3, 1.8k series grid stopper.

The 6SN7 is operating fairly linearly and comfortably.
Without Ck bypass, the driver thd reduces, but then overall thd rises
a lot since less even order Dn cancelation takes place.

The fully bypassed Rk on the 6SN7 gives lowish Ra of about 5k for the
paralleled tube
and is thus a sufficiently low enough drive resistance to enhance the
micro detail behaviour of the
2A3, ( very necessary imho to get the best out of not just a triode
output tube,
but ALL output tubes.)

The input tube is 1/2 a 12AU7 of unknown lineage; it measured nicely,
and I like the 12AU7 for inputs; its warm, accurate, and sounds
glorious.

Its Rk is 1.8k, and also bypassed with 470uF, and taken then to 100
ohms
for
the global NFB to be applied.
RL is 50k, 0.47uF to a network for LF gain stepping, 1M+0.033uF
plus 220k, typical in many of my amps to vastly
improve the bass stability when the 12dB of global FB is applied.

The FB resistor divider network is 750 ohms to 100 ohms
with a phase tweaker bypass cap across the 750 ohms = 1,000 pF.
There is a 470pF plus 2.7k zobel network connected from the
driver grid to 0V to control the HF gain and ultimate phase shift of
the

12AU7 to 6SN7 interface.
A further 5.6ohms+0.47uF Zobel network is across the OPT secondary,
and finally I got the amp to be fairly ring free when connected to
any value of cap without a pure R load, and when using a square wave.
Open loop BW with all compensation zobels in place was 20Hz to 20kHz,
-3dB,
and with 12 dB of FB the full power BW is 5Hz to 55kHz, 5 ohms.
It remains the same at lower levels of power.

A 5 kHz square wave is a bit ragged due to the mentioned OPT design
simplicity,
but the sine wave response between 30Hz and 20hHz right up to clipping
is dead flat.

A 50k Alps Black pot is used for the gain control.

Input sensitivity with 12dB applied global NFB is 0.7Vrms.
The amp's use with an CD player is fine.
Just no need for any preamp.

The sound is that of a far more powerful amplifier,
with tremendous sense of rightness, instrument detail, warmth without
muddle, not the slightest hint of any lack of bass, the usual beautiful
mids, and detailed top end.

The amp measures well at less than 1% thd at 4 watts into 5 ohms,
mainly all 2H.
But at normal levels of a watt the 3H and other H are present below the
2H
which can be seen on the CRO when monitoring the THD at all levels.
Ro is 0.47 ohm, and although my speakers vary between
4 and 20ohms, the sound appears firm, well timbred, and there isn't any
hint
of the sound being that from an inadequate amplifier.

I played Handel's water music, the sound track of 'The Pianist' for my
tests plus
a not so wonderful Naxos CD, 'The Best of Bach'.

Who says SET amps suck?

Certainly not I!.

Methinks that if the owner wanted more power, he could simply swap the
2A3 for a KT90 since the PT has a 6.3V heater winding, and then
remove the series R I have placed in the B+ lines to trim the B+
to where I want it, and with 270V, and with the UL tap on the
OPT that is provided, maybe 9+ watts of SEUL would be available.

The now unused 1670 OPT UL tap is at 40%.
But it could be at 60%, if you use the plate winding reversed,
thus further drifting a tetrode towards triode, but still not
suffering a huge loss of power due to grid current limitations.

300B could also be used, and with slightly more Ia,
but with the same low Ea, thus suiting moderate power and good matching
to
low value loads, which is a major failing in many SET amps;
they try to match so max power is at 8ohms, but that is
nearly always wrong with modern speakers, and
max power should occur at 3 or 4 ohms.


Patrick Turner.







  #24   Report Post  
Fabio Berutti
 
Posts: n/a
Default

Just a brief note concerning the cost of a PP arrangement: there are still
some good NOS Svetlana 6S4S for sale (or 6C4C as it looks in Cyrillic), a
6.3v-octal base version of the original dual-plate 2A3, which cost some 25$
per tube, if You spend some time "googling" around (http://rvd.gstube.com/
or http://www.tubes.ru/GlassTubes.html). 100$ for the whole power tube
complement is not that much, I'd say. Sure, if You want four RCA single
plate NOS the figure goes up quite a bit.

Ciao

Fabio


"Andre Jute" ha scritto nel messaggio
ups.com...
Definitely.

One of the finest amps I ever heard was a PP 2A3 from the late lamented
Audio Innovations called IIRC The First.

In Patrick's application SE 2A3 will be more than adequately powerful
to drive the HF, which really doesn't require even a whole watt even on
orchestral fortes. (Experiment: make a filter to lose everything below
8K5Hz. Listen to the remainder. It is a sort of buzz, not music. Its
actual power content is fractional. Most people a lot younger than the
average age of RATs cannot hear that there is a difference between one
of my Impresarion with the tweeter and one without, the one without
tapering off about 10kHz.)

But I have my doubts about SE 2A3 even with a sensitive fullrange horn.
A DHT is usually decently silent but I like further to silence it with
a high load on the plate. When you do that the power falls alarmingly,
soon to under one watt, which is not too hot on even a Lowther horn if
you want to play orchestral music. With a Lowther horn (c100dB/w/m) I
like about 4W of very silent power, which is why I use 300B instead of
2A3. To address Fabio's remarks, I don't think a 3.5W 2A3 SE with a
97dB speaker is a rock'n'roll combination. Far too much powere required
in those bass "transients" which is rock'n'roll can go on forever.

Also, while theoretically I like the *concept* of PP DHT, I am a
Calvinist who shrinks from such expense when a triode-linked PP EL34
amp will give you the same power and 99 per cent of the sound for half
the price. There used to be a salesman called Zip on RAO (he was
disgraced when he couldn't distinguish one cable from another); Zip
used to tell people who complained about the price of the amps he sold
that they lacked commitment to their music, as if how much you spend is
a mark of merit. Zip was full of ****. I have passion for my music but
there is no reason to let it interfere with common sense.

Andre Jute
Gotta sleep. E&OE.

Fabio Berutti wrote:
A well-known manufacturer of 400W amps like Mr. Turner is someone to
trust,
when he says that as low as 4W can still be enough, if all the "sound"
chain
is properly set. I treasure my own 2A3, particularly for its
"effortless"
sound, which is not "weak" or "tubey" indeed. The only limit of the 2A3
SE
is "loud" music: my LS are about 97 dB, but when listening the Stones,
well,
Mick simply isn't shouting and Keith's guitar isn't as mean and nasty as
it
should.
Nevertheless, this is not a real limit: a HiFi set is a sort of a musical
instrument. Just like a Stratocaster is not considered "bad" 'cause it's
not suited for playing Bach, a 2A3 SE is not "bad" 'cause it's not good
for
AC/DC (the Oz group, not the power supply); mr Turner correctly quoted
that
the amp was very good for playing chamber music, not trash metal. In
fact,
I agree with Mr. DeWaal: a 2A3 PP (or a 6B4G) is probably the closest
thing
to the "perfect" sound: DHT, relatively low driving requirements,
relatively
low output impedance (3K5 typ), reasonable B+, and an output power of
about
10-12W which is enough even for the 9th symphony's chorus or the
beginning
of "Back in black"... if You have efficient boxes and your neighbors are
not
deaf.
There are thousands of "viable" circuits, but I'm still persuaded that
from
an engineering point it's better to avoid problems (or distortion) than
to
create some and then try to get rid of them. The 2A3 provides a nearly
perfect transfer function of its own, therefore the "tinkering" required
to
make it "20 to 20k" can be kept to a minimum, which ultimately results in
no
unpredictable "electronic traps", fixing some bug here just to make a
worse
one somewhere else.

The only problem with a 2A3SE with good LSs is that suddenly You really
hear
how badly many CDs are recorded. Some jazz LPs from the Fifties are lots
better.

Ciao

Fabio



"Patrick Turner" ha scritto nel messaggio
...
I finally have hooked up the stereo amp which uses 2A3
to my speakers which are about 90dB sensitivity.
I find I could listen all day and night to this underpowered
amplifier.
Whatever its doing it is doing it RIGHT.

The conditions are as follows.

Power tranny is Hammond type 370FX, and with
a 240V: 2 x 2.5V filament tranny.
Hammond 10H choke used with a quad of Sonic Frontier
PS caps of 1,100 uF each, so that with seriesed caps
I have 550uF, 10H, 550uF, as the CLC to supply power to the
pair of amp channels.
Rectifiers are IN5408 SS diodes. I don't strictly believe in tube
rectifiers;
I like them, I even use them sometimes; I just don't think they are
indispensible.
But in this case the use of a tube rectifier would have reduced the
available B+
and forced me to use fixed bias, which I don't like for any SE amps.

No need to dual mono power supplies.
180uF used to further filter the input and driver stages.


Output tubes are 2A3, RCA, NOS?, maybe used, not sure.
Ea = +270V, Ia = 57mA, cathode bias with 820ohms
bypassed with good quality 100V x 470uF.
heaters are AC 2.5V with a pot for hum nulling.

OPT is a 2.5k : 4/8/16 Hammond 25 watt rated SET gapped OPT
type 1627SE.

OPT is set up to match 2.5k to 4ohms, but I find 5 ohms is the most
correct load.

At 4Watts I get excellent open loop BW with this OPT
and freedom from saturation, of which there is only a slight trace at
about
7 Hz.

The OPT has queer resonances above 30kHz, makinf the use of
global NFB difficult for ppl with no clue about how to overcome such
connundrums.
It must be due to primary being wound close to the secondary,
and the absence of enough interleavings of windings, and the absence of
sufficient
insulation thickness.
Nevertheless, the 1627SE did turn out to be very usable, and sound is
glorious.

Driver tube is an ancient Radiotron 'made in australia' 6SN7,
used but OK. 1k Rk bypassed with 470uF, RL = 34k, 0.47 uF Wima
coupling
cap,
150k grid bias R for 2A3, 1.8k series grid stopper.

The 6SN7 is operating fairly linearly and comfortably.
Without Ck bypass, the driver thd reduces, but then overall thd rises
a lot since less even order Dn cancelation takes place.

The fully bypassed Rk on the 6SN7 gives lowish Ra of about 5k for the
paralleled tube
and is thus a sufficiently low enough drive resistance to enhance the
micro detail behaviour of the
2A3, ( very necessary imho to get the best out of not just a triode
output tube,
but ALL output tubes.)

The input tube is 1/2 a 12AU7 of unknown lineage; it measured nicely,
and I like the 12AU7 for inputs; its warm, accurate, and sounds
glorious.

Its Rk is 1.8k, and also bypassed with 470uF, and taken then to 100
ohms
for
the global NFB to be applied.
RL is 50k, 0.47uF to a network for LF gain stepping, 1M+0.033uF
plus 220k, typical in many of my amps to vastly
improve the bass stability when the 12dB of global FB is applied.

The FB resistor divider network is 750 ohms to 100 ohms
with a phase tweaker bypass cap across the 750 ohms = 1,000 pF.
There is a 470pF plus 2.7k zobel network connected from the
driver grid to 0V to control the HF gain and ultimate phase shift of
the

12AU7 to 6SN7 interface.
A further 5.6ohms+0.47uF Zobel network is across the OPT secondary,
and finally I got the amp to be fairly ring free when connected to
any value of cap without a pure R load, and when using a square wave.
Open loop BW with all compensation zobels in place was 20Hz to 20kHz,
-3dB,
and with 12 dB of FB the full power BW is 5Hz to 55kHz, 5 ohms.
It remains the same at lower levels of power.

A 5 kHz square wave is a bit ragged due to the mentioned OPT design
simplicity,
but the sine wave response between 30Hz and 20hHz right up to clipping
is dead flat.

A 50k Alps Black pot is used for the gain control.

Input sensitivity with 12dB applied global NFB is 0.7Vrms.
The amp's use with an CD player is fine.
Just no need for any preamp.

The sound is that of a far more powerful amplifier,
with tremendous sense of rightness, instrument detail, warmth without
muddle, not the slightest hint of any lack of bass, the usual beautiful
mids, and detailed top end.

The amp measures well at less than 1% thd at 4 watts into 5 ohms,
mainly all 2H.
But at normal levels of a watt the 3H and other H are present below the
2H
which can be seen on the CRO when monitoring the THD at all levels.
Ro is 0.47 ohm, and although my speakers vary between
4 and 20ohms, the sound appears firm, well timbred, and there isn't any
hint
of the sound being that from an inadequate amplifier.

I played Handel's water music, the sound track of 'The Pianist' for my
tests plus
a not so wonderful Naxos CD, 'The Best of Bach'.

Who says SET amps suck?

Certainly not I!.

Methinks that if the owner wanted more power, he could simply swap the
2A3 for a KT90 since the PT has a 6.3V heater winding, and then
remove the series R I have placed in the B+ lines to trim the B+
to where I want it, and with 270V, and with the UL tap on the
OPT that is provided, maybe 9+ watts of SEUL would be available.

The now unused 1670 OPT UL tap is at 40%.
But it could be at 60%, if you use the plate winding reversed,
thus further drifting a tetrode towards triode, but still not
suffering a huge loss of power due to grid current limitations.

300B could also be used, and with slightly more Ia,
but with the same low Ea, thus suiting moderate power and good matching
to
low value loads, which is a major failing in many SET amps;
they try to match so max power is at 8ohms, but that is
nearly always wrong with modern speakers, and
max power should occur at 3 or 4 ohms.


Patrick Turner.







  #25   Report Post  
Patrick Turner
 
Posts: n/a
Default



VinylBigot wrote:

Absolutely agree. I've gone through the whole gambit of PP tube amps of all
power sizes, moved on to SET's and settled on the 2A3 as having the most
truly beautiful and natural sound. I wrote a piece on a few forums asking
for other opinions, and most agreed that the 2A3 won out over 300B and 45.
I felt that the 45 gave a percieved "cleaner" sound, but it was almost
clinical--and not natural. I like a sound that is as close to a classical
live concert in a good hall, as possible. There is a fair amount of
reflection which colors the sound in a live concert--the 2A3's seem to do a
very good job of mimicking this. I also found that the supposed improvement
from cobalt OPT's was not to my liking either.


Funny you should mention cobalt. In Japan they have made a cult of the SET.
One guru who heads the cult went up a high mountain for a month
to meditate on the effects of cobalt on the sound.
He eventually came down with a better idea about the % of cobalt.
But I knew his next door neighbour, and he said that this guru's missus was a
terrible cook,
and that the guy just took a break up the hill really because the girls in the
kiosk
smiled while they served him a lot better tucker.....

But then we have to consider the case of Hiroyasu Kondo.
I doubt he's ever been known for eating kiosk food up high mountains
but it does seem he founded Audio Note in Japan in 1976
when he must have been quite a cool smart young dude.

He cobbled together the SET 211 Ongaku amplifier which costs an extraordinary
amount, as much a Mercedes Benz, or a few villas in Argentina...
Anyway, I am not here to argue the cost, but he uses at least several pounds of
silver per channel
as winding wire in the trannies, then he uses 50% nickel in the OPTs.
I assume the 50% is in the form of alternately placed laminations.

One could do worse than follow his practices.

In my case with the little 2A3 amp I was advised by a cash strapped hi-fi
fanatic
for whom I made the amps to use Hammond OPTs, so no silver or nickel.

But the OPTs are rated for 25 watts, or 10Vrms into 4 ohms,
the 2A3 could only mannage to pump 4 watts into 4 ohms, ie, 4Vrms,
so the tranny is working with a small fraction of DC in the core, and a
small fraction of the AC across the winding, so I guess this helps suppress the
bad things that
do occur when audio is pumped through a transformer.
Mind you, such bad things are piddlingly small considerations
in any well designed amp.
But in the case of the 2A3, there isn't much horribility in the iron to complain
about,
even though its is Hammond iron, which is a cheap option for any diyer.

So how much better is the sound of a 1/2 watt from Mr Kondo's amp compared to
something anyone here might cobble together?

I leave that for you guys to find out.

Meanwhile, one Peter Qvortrop has registered the names of Audio Note in
several countries without the consent or permission of Mr Kondo.
Qvortrop has had an article about his 211 SET amps in the august 2005 issue,
and unfortunately, I am not very impressed.
There is no silver or nickel in the OPTs, yet the price will be 35,000 pounds
for the stereo amp.

I raise my hat to these guys, why, with such high prices there's a chance
we might do ok trying to sell the same performance for 3,500 pounds.





I've gone through a whole set of 2A3's NOS to find the best. My favorite is
a pair of no-name RadTel's from the 30's. Next is RCA silver, and then
National Union, then RCA black. The SovTeks and ValveArt's just plain
stink.


But you gotta worry about the driver/input tubes, and the OPTs.
To my mind the system is the sum of the total...



I use Lowthers which gives plently of volume in my listening room. Even a
71A amp has enough power for me.


I would think 4 watts for Lowthers to be plenty.
I know a guy with a 1 watt amp who had enough for most listening...

Patrick Turner.



"Patrick Turner" wrote in message
...
I finally have hooked up the stereo amp which uses 2A3
to my speakers which are about 90dB sensitivity.
I find I could listen all day and night to this underpowered
amplifier.
Whatever its doing it is doing it RIGHT.

The conditions are as follows.

Power tranny is Hammond type 370FX, and with
a 240V: 2 x 2.5V filament tranny.
Hammond 10H choke used with a quad of Sonic Frontier
PS caps of 1,100 uF each, so that with seriesed caps
I have 550uF, 10H, 550uF, as the CLC to supply power to the
pair of amp channels.
Rectifiers are IN5408 SS diodes. I don't strictly believe in tube
rectifiers;
I like them, I even use them sometimes; I just don't think they are
indispensible.
But in this case the use of a tube rectifier would have reduced the
available B+
and forced me to use fixed bias, which I don't like for any SE amps.

No need to dual mono power supplies.
180uF used to further filter the input and driver stages.


Output tubes are 2A3, RCA, NOS?, maybe used, not sure.
Ea = +270V, Ia = 57mA, cathode bias with 820ohms
bypassed with good quality 100V x 470uF.
heaters are AC 2.5V with a pot for hum nulling.

OPT is a 2.5k : 4/8/16 Hammond 25 watt rated SET gapped OPT
type 1627SE.

OPT is set up to match 2.5k to 4ohms, but I find 5 ohms is the most
correct load.

At 4Watts I get excellent open loop BW with this OPT
and freedom from saturation, of which there is only a slight trace at
about
7 Hz.

The OPT has queer resonances above 30kHz, makinf the use of
global NFB difficult for ppl with no clue about how to overcome such
connundrums.
It must be due to primary being wound close to the secondary,
and the absence of enough interleavings of windings, and the absence of
sufficient
insulation thickness.
Nevertheless, the 1627SE did turn out to be very usable, and sound is
glorious.

Driver tube is an ancient Radiotron 'made in australia' 6SN7,
used but OK. 1k Rk bypassed with 470uF, RL = 34k, 0.47 uF Wima coupling
cap,
150k grid bias R for 2A3, 1.8k series grid stopper.

The 6SN7 is operating fairly linearly and comfortably.
Without Ck bypass, the driver thd reduces, but then overall thd rises
a lot since less even order Dn cancelation takes place.

The fully bypassed Rk on the 6SN7 gives lowish Ra of about 5k for the
paralleled tube
and is thus a sufficiently low enough drive resistance to enhance the
micro detail behaviour of the
2A3, ( very necessary imho to get the best out of not just a triode
output tube,
but ALL output tubes.)

The input tube is 1/2 a 12AU7 of unknown lineage; it measured nicely,
and I like the 12AU7 for inputs; its warm, accurate, and sounds
glorious.

Its Rk is 1.8k, and also bypassed with 470uF, and taken then to 100 ohms
for
the global NFB to be applied.
RL is 50k, 0.47uF to a network for LF gain stepping, 1M+0.033uF
plus 220k, typical in many of my amps to vastly
improve the bass stability when the 12dB of global FB is applied.

The FB resistor divider network is 750 ohms to 100 ohms
with a phase tweaker bypass cap across the 750 ohms = 1,000 pF.
There is a 470pF plus 2.7k zobel network connected from the
driver grid to 0V to control the HF gain and ultimate phase shift of the

12AU7 to 6SN7 interface.
A further 5.6ohms+0.47uF Zobel network is across the OPT secondary,
and finally I got the amp to be fairly ring free when connected to
any value of cap without a pure R load, and when using a square wave.
Open loop BW with all compensation zobels in place was 20Hz to 20kHz,
-3dB,
and with 12 dB of FB the full power BW is 5Hz to 55kHz, 5 ohms.
It remains the same at lower levels of power.

A 5 kHz square wave is a bit ragged due to the mentioned OPT design
simplicity,
but the sine wave response between 30Hz and 20hHz right up to clipping
is dead flat.

A 50k Alps Black pot is used for the gain control.

Input sensitivity with 12dB applied global NFB is 0.7Vrms.
The amp's use with an CD player is fine.
Just no need for any preamp.

The sound is that of a far more powerful amplifier,
with tremendous sense of rightness, instrument detail, warmth without
muddle, not the slightest hint of any lack of bass, the usual beautiful
mids, and detailed top end.

The amp measures well at less than 1% thd at 4 watts into 5 ohms,
mainly all 2H.
But at normal levels of a watt the 3H and other H are present below the
2H
which can be seen on the CRO when monitoring the THD at all levels.
Ro is 0.47 ohm, and although my speakers vary between
4 and 20ohms, the sound appears firm, well timbred, and there isn't any
hint
of the sound being that from an inadequate amplifier.

I played Handel's water music, the sound track of 'The Pianist' for my
tests plus
a not so wonderful Naxos CD, 'The Best of Bach'.

Who says SET amps suck?

Certainly not I!.

Methinks that if the owner wanted more power, he could simply swap the
2A3 for a KT90 since the PT has a 6.3V heater winding, and then
remove the series R I have placed in the B+ lines to trim the B+
to where I want it, and with 270V, and with the UL tap on the
OPT that is provided, maybe 9+ watts of SEUL would be available.

The now unused 1670 OPT UL tap is at 40%.
But it could be at 60%, if you use the plate winding reversed,
thus further drifting a tetrode towards triode, but still not
suffering a huge loss of power due to grid current limitations.

300B could also be used, and with slightly more Ia,
but with the same low Ea, thus suiting moderate power and good matching
to
low value loads, which is a major failing in many SET amps;
they try to match so max power is at 8ohms, but that is
nearly always wrong with modern speakers, and
max power should occur at 3 or 4 ohms.


Patrick Turner.







  #26   Report Post  
Sander deWaal
 
Posts: n/a
Default

"Fabio Berutti" said:

I agree with Mr. DeWaal: a 2A3 PP (or a 6B4G) is probably the closest thing
to the "perfect" sound: DHT, relatively low driving requirements, relatively
low output impedance (3K5 typ), reasonable B+, and an output power of about
10-12W which is enough even for the 9th symphony's chorus or the beginning
of "Back in black"... if You have efficient boxes and your neighbors are not
deaf.



Heh!
I have 84 dB/w/m Maggies connected, and this amp plays to
earshattering levels if you want to.

Really, it has the balls of my hybrid MOSFET amp, but with more
finesse.

A good amp, and probably the last one I'll ever build :-)

--

"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005
  #27   Report Post  
Sander deWaal
 
Posts: n/a
Default

"Fabio Berutti" said:

As per the output transformer, any good 3k5 unit will fit. BTW, being a PP
unit, it can be fed AC to the filaments, no problems. I'd keep separate
windings for each tube in order to have each one individually biased; this
allows to use any tube and it is safer in case of sudden failure of one
tube, but it is obviously easier and cheaper to have the 2 tubes of the PP
pair fed by a single transformer winding, having a center tap referred to
ground by the common cathode bias resistor (+capacitor). In this case, in
order to match quiescent current, tubes shall be matched on a good tester
(or bought from a dependable source as matched pairs),



Personally, I'm not a fan of common cathode resistors.
I used separates, each bypassed with a good 220uF/100V cap (philips
long life, good enough for me).
That way, I don't have to worry about unmatched pairs drawing unequal
currents, or worse, one tube taking it all while the other sits almost
idle.

--

"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005
  #28   Report Post  
Patrick Turner
 
Posts: n/a
Default



Sander deWaal wrote:

"Fabio Berutti" said:

As per the output transformer, any good 3k5 unit will fit. BTW, being a PP
unit, it can be fed AC to the filaments, no problems. I'd keep separate
windings for each tube in order to have each one individually biased; this
allows to use any tube and it is safer in case of sudden failure of one
tube, but it is obviously easier and cheaper to have the 2 tubes of the PP
pair fed by a single transformer winding, having a center tap referred to
ground by the common cathode bias resistor (+capacitor). In this case, in
order to match quiescent current, tubes shall be matched on a good tester
(or bought from a dependable source as matched pairs),


Personally, I'm not a fan of common cathode resistors.
I used separates, each bypassed with a good 220uF/100V cap (philips
long life, good enough for me).
That way, I don't have to worry about unmatched pairs drawing unequal
currents, or worse, one tube taking it all while the other sits almost
idle.


1,000 uF are even better.

Patrick Turner.



--

"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005


  #29   Report Post  
Ian Iveson
 
Posts: n/a
Default

"Patrick Turner" wrote

...stuff about Audio Note, below...


The Audio Note UK story is possibly quite interesting. A few points
to qualify Patrick's typically bitter and twisted comments.

Kondo no longer uses the Audio Note name.

Audio Note in the UK produce a full range of valve amps, and have
recently hived off the Audio Note UK kit and component business.

Continuing its own tradition, Audio Note in the UK offer several
"levels" of quality. The top level includes all silver wiring,
including interstage and output transformer windings, and 50 or 55%
nickel OPT core.

http://www.audionote.co.uk/

AFAIK the core is a nickel alloy. If you can thread your way through
to the current kit and component suppliers I imagine there are some
details. Or look on the Lundahl site, or even that of the waffly
Magnaquest. Or search under "nickel iron" core. Any kind of finding
out would do, really. Could save embarrassment.

cheers, Ian

But then we have to consider the case of Hiroyasu Kondo.
I doubt he's ever been known for eating kiosk food up high
mountains
but it does seem he founded Audio Note in Japan in 1976
when he must have been quite a cool smart young dude.

He cobbled together the SET 211 Ongaku amplifier which costs an
extraordinary
amount, as much a Mercedes Benz, or a few villas in Argentina...
Anyway, I am not here to argue the cost, but he uses at least
several pounds of
silver per channel
as winding wire in the trannies, then he uses 50% nickel in the
OPTs.
I assume the 50% is in the form of alternately placed laminations.

One could do worse than follow his practices.

In my case with the little 2A3 amp I was advised by a cash
strapped hi-fi
fanatic
for whom I made the amps to use Hammond OPTs, so no silver or
nickel.

But the OPTs are rated for 25 watts, or 10Vrms into 4 ohms,
the 2A3 could only mannage to pump 4 watts into 4 ohms, ie, 4Vrms,
so the tranny is working with a small fraction of DC in the core,
and a
small fraction of the AC across the winding, so I guess this helps
suppress the
bad things that
do occur when audio is pumped through a transformer.
Mind you, such bad things are piddlingly small considerations
in any well designed amp.
But in the case of the 2A3, there isn't much horribility in the
iron to complain
about,
even though its is Hammond iron, which is a cheap option for any
diyer.

So how much better is the sound of a 1/2 watt from Mr Kondo's amp
compared to
something anyone here might cobble together?

I leave that for you guys to find out.

Meanwhile, one Peter Qvortrop has registered the names of Audio
Note in
several countries without the consent or permission of Mr Kondo.
Qvortrop has had an article about his 211 SET amps in the august
2005 issue,
and unfortunately, I am not very impressed.
There is no silver or nickel in the OPTs, yet the price will be
35,000 pounds
for the stereo amp.

I raise my hat to these guys, why, with such high prices there's a
chance
we might do ok trying to sell the same performance for 3,500
pounds.



  #30   Report Post  
Patrick Turner
 
Posts: n/a
Default



Ian Iveson wrote:

"Patrick Turner" wrote

...stuff about Audio Note, below...


The Audio Note UK story is possibly quite interesting. A few points
to qualify Patrick's typically bitter and twisted comments.


Total BULL**** from a pomme ****wit!!!

You really like spreading lies when its YOU who is the bitter twisted
hot air bag.

You have top posted over my post to avoid having to reply accurately
within the context.


Kondo no longer uses the Audio Note name.


I only reported what I had read in Hi-Fi News.

I thought they were very kind to Qvortrop who didn't deserve it and that
the
211 amp described in august 2005 issue was nowhere near the quality of
the japanese master.



Audio Note in the UK produce a full range of valve amps, and have
recently hived off the Audio Note UK kit and component business.

Continuing its own tradition, Audio Note in the UK offer several
"levels" of quality. The top level includes all silver wiring,
including interstage and output transformer windings, and 50 or 55%
nickel OPT core.

http://www.audionote.co.uk/

AFAIK the core is a nickel alloy. If you can thread your way through
to the current kit and component suppliers I imagine there are some
details. Or look on the Lundahl site, or even that of the waffly
Magnaquest. Or search under "nickel iron" core. Any kind of finding
out would do, really. Could save embarrassment.


I only quoted what I read in Hi-Fi News.

A customer of mine was mightily UNIMPRESSED by the
bull**** in the magazine, which he brought to me for a look.

I never buy Hi-Fi News ( or Stereophile ) et all.

You have been keen to point out my error, which was Hi-Fi world's error
if there was indeed any error.
It seemed like the amp pictured in Hi-Fi World had much plainer gear
used in its construction
compared to the original and much more expensive japanese version.

But YOU have not bothered to look to finding out any real facts about
the issue.

And BTW, I was certainly not obliged to suss out what Magnequest
or Lundahl used in their cores.

Get off your lazy BUTT Ian, and do something useful.


I just build amps.

Patrick Turner.



cheers, Ian

But then we have to consider the case of Hiroyasu Kondo.
I doubt he's ever been known for eating kiosk food up high
mountains
but it does seem he founded Audio Note in Japan in 1976
when he must have been quite a cool smart young dude.

He cobbled together the SET 211 Ongaku amplifier which costs an
extraordinary
amount, as much a Mercedes Benz, or a few villas in Argentina...
Anyway, I am not here to argue the cost, but he uses at least
several pounds of
silver per channel
as winding wire in the trannies, then he uses 50% nickel in the
OPTs.
I assume the 50% is in the form of alternately placed laminations.

One could do worse than follow his practices.

In my case with the little 2A3 amp I was advised by a cash
strapped hi-fi
fanatic
for whom I made the amps to use Hammond OPTs, so no silver or
nickel.

But the OPTs are rated for 25 watts, or 10Vrms into 4 ohms,
the 2A3 could only mannage to pump 4 watts into 4 ohms, ie, 4Vrms,
so the tranny is working with a small fraction of DC in the core,
and a
small fraction of the AC across the winding, so I guess this helps
suppress the
bad things that
do occur when audio is pumped through a transformer.
Mind you, such bad things are piddlingly small considerations
in any well designed amp.
But in the case of the 2A3, there isn't much horribility in the
iron to complain
about,
even though its is Hammond iron, which is a cheap option for any
diyer.

So how much better is the sound of a 1/2 watt from Mr Kondo's amp
compared to
something anyone here might cobble together?

I leave that for you guys to find out.

Meanwhile, one Peter Qvortrop has registered the names of Audio
Note in
several countries without the consent or permission of Mr Kondo.
Qvortrop has had an article about his 211 SET amps in the august
2005 issue,
and unfortunately, I am not very impressed.
There is no silver or nickel in the OPTs, yet the price will be
35,000 pounds
for the stereo amp.

I raise my hat to these guys, why, with such high prices there's a
chance
we might do ok trying to sell the same performance for 3,500
pounds.




  #31   Report Post  
John Stewart
 
Posts: n/a
Default

Patrick Turner wrote:

I finally have hooked up the stereo amp which uses 2A3
to my speakers which are about 90dB sensitivity.
I find I could listen all day and night to this underpowered
amplifier.
Whatever its doing it is doing it RIGHT.

The conditions are as follows.

Power tranny is Hammond type 370FX, and with
a 240V: 2 x 2.5V filament tranny.
Hammond 10H choke used with a quad of Sonic Frontier
PS caps of 1,100 uF each, so that with seriesed caps
I have 550uF, 10H, 550uF, as the CLC to supply power to the
pair of amp channels.
Rectifiers are IN5408 SS diodes. I don't strictly believe in tube
rectifiers;
I like them, I even use them sometimes; I just don't think they are
indispensible.
But in this case the use of a tube rectifier would have reduced the
available B+
and forced me to use fixed bias, which I don't like for any SE amps.

No need to dual mono power supplies.
180uF used to further filter the input and driver stages.

Output tubes are 2A3, RCA, NOS?, maybe used, not sure.
Ea = +270V, Ia = 57mA, cathode bias with 820ohms
bypassed with good quality 100V x 470uF.
heaters are AC 2.5V with a pot for hum nulling.

OPT is a 2.5k : 4/8/16 Hammond 25 watt rated SET gapped OPT
type 1627SE.

OPT is set up to match 2.5k to 4ohms, but I find 5 ohms is the most
correct load.

At 4Watts I get excellent open loop BW with this OPT
and freedom from saturation, of which there is only a slight trace at
about
7 Hz.

The OPT has queer resonances above 30kHz, makinf the use of
global NFB difficult for ppl with no clue about how to overcome such
connundrums.
It must be due to primary being wound close to the secondary,
and the absence of enough interleavings of windings, and the absence of
sufficient
insulation thickness.
Nevertheless, the 1627SE did turn out to be very usable, and sound is
glorious.

Driver tube is an ancient Radiotron 'made in australia' 6SN7,
used but OK. 1k Rk bypassed with 470uF, RL = 34k, 0.47 uF Wima coupling
cap,
150k grid bias R for 2A3, 1.8k series grid stopper.

The 6SN7 is operating fairly linearly and comfortably.
Without Ck bypass, the driver thd reduces, but then overall thd rises
a lot since less even order Dn cancelation takes place.

The fully bypassed Rk on the 6SN7 gives lowish Ra of about 5k for the
paralleled tube
and is thus a sufficiently low enough drive resistance to enhance the
micro detail behaviour of the
2A3, ( very necessary imho to get the best out of not just a triode
output tube,
but ALL output tubes.)

The input tube is 1/2 a 12AU7 of unknown lineage; it measured nicely,
and I like the 12AU7 for inputs; its warm, accurate, and sounds
glorious.

Its Rk is 1.8k, and also bypassed with 470uF, and taken then to 100 ohms
for
the global NFB to be applied.
RL is 50k, 0.47uF to a network for LF gain stepping, 1M+0.033uF
plus 220k, typical in many of my amps to vastly
improve the bass stability when the 12dB of global FB is applied.

The FB resistor divider network is 750 ohms to 100 ohms
with a phase tweaker bypass cap across the 750 ohms = 1,000 pF.
There is a 470pF plus 2.7k zobel network connected from the
driver grid to 0V to control the HF gain and ultimate phase shift of the

12AU7 to 6SN7 interface.
A further 5.6ohms+0.47uF Zobel network is across the OPT secondary,
and finally I got the amp to be fairly ring free when connected to
any value of cap without a pure R load, and when using a square wave.
Open loop BW with all compensation zobels in place was 20Hz to 20kHz,
-3dB,
and with 12 dB of FB the full power BW is 5Hz to 55kHz, 5 ohms.
It remains the same at lower levels of power.

A 5 kHz square wave is a bit ragged due to the mentioned OPT design
simplicity,
but the sine wave response between 30Hz and 20hHz right up to clipping
is dead flat.

A 50k Alps Black pot is used for the gain control.

Input sensitivity with 12dB applied global NFB is 0.7Vrms.
The amp's use with an CD player is fine.
Just no need for any preamp.

The sound is that of a far more powerful amplifier,
with tremendous sense of rightness, instrument detail, warmth without
muddle, not the slightest hint of any lack of bass, the usual beautiful
mids, and detailed top end.

The amp measures well at less than 1% thd at 4 watts into 5 ohms,
mainly all 2H.
But at normal levels of a watt the 3H and other H are present below the
2H
which can be seen on the CRO when monitoring the THD at all levels.
Ro is 0.47 ohm, and although my speakers vary between
4 and 20ohms, the sound appears firm, well timbred, and there isn't any
hint
of the sound being that from an inadequate amplifier.

I played Handel's water music, the sound track of 'The Pianist' for my
tests plus
a not so wonderful Naxos CD, 'The Best of Bach'.

Who says SET amps suck?

Certainly not I!.

Methinks that if the owner wanted more power, he could simply swap the
2A3 for a KT90 since the PT has a 6.3V heater winding, and then
remove the series R I have placed in the B+ lines to trim the B+
to where I want it, and with 270V, and with the UL tap on the
OPT that is provided, maybe 9+ watts of SEUL would be available.

The now unused 1670 OPT UL tap is at 40%.
But it could be at 60%, if you use the plate winding reversed,
thus further drifting a tetrode towards triode, but still not
suffering a huge loss of power due to grid current limitations.

300B could also be used, and with slightly more Ia,
but with the same low Ea, thus suiting moderate power and good matching
to
low value loads, which is a major failing in many SET amps;
they try to match so max power is at 8ohms, but that is
nearly always wrong with modern speakers, and
max power should occur at 3 or 4 ohms.

Patrick Turner.


Whats this I see? Patrick T. using Hammond? Or something brought in by a
customer?

I'm back into sales again. Lots of manual labour on the house this summer as
well. Not much time for tubes.

But if I get time I have a couple of interesting projects in mind. One is a
hybrid. But don't know when.

Cheers, John



  #32   Report Post  
Patrick Turner
 
Posts: n/a
Default



John Stewart wrote:

Patrick Turner wrote:

I finally have hooked up the stereo amp which uses 2A3
to my speakers which are about 90dB sensitivity.
I find I could listen all day and night to this underpowered
amplifier.
Whatever its doing it is doing it RIGHT.

The conditions are as follows.

Power tranny is Hammond type 370FX, and with
a 240V: 2 x 2.5V filament tranny.
Hammond 10H choke used with a quad of Sonic Frontier
PS caps of 1,100 uF each, so that with seriesed caps
I have 550uF, 10H, 550uF, as the CLC to supply power to the
pair of amp channels.
Rectifiers are IN5408 SS diodes. I don't strictly believe in tube
rectifiers;
I like them, I even use them sometimes; I just don't think they are
indispensible.
But in this case the use of a tube rectifier would have reduced the
available B+
and forced me to use fixed bias, which I don't like for any SE amps.

No need to dual mono power supplies.
180uF used to further filter the input and driver stages.

Output tubes are 2A3, RCA, NOS?, maybe used, not sure.
Ea = +270V, Ia = 57mA, cathode bias with 820ohms
bypassed with good quality 100V x 470uF.
heaters are AC 2.5V with a pot for hum nulling.

OPT is a 2.5k : 4/8/16 Hammond 25 watt rated SET gapped OPT
type 1627SE.

OPT is set up to match 2.5k to 4ohms, but I find 5 ohms is the most
correct load.

At 4Watts I get excellent open loop BW with this OPT
and freedom from saturation, of which there is only a slight trace at
about
7 Hz.

The OPT has queer resonances above 30kHz, makinf the use of
global NFB difficult for ppl with no clue about how to overcome such
connundrums.
It must be due to primary being wound close to the secondary,
and the absence of enough interleavings of windings, and the absence of
sufficient
insulation thickness.
Nevertheless, the 1627SE did turn out to be very usable, and sound is
glorious.

Driver tube is an ancient Radiotron 'made in australia' 6SN7,
used but OK. 1k Rk bypassed with 470uF, RL = 34k, 0.47 uF Wima coupling
cap,
150k grid bias R for 2A3, 1.8k series grid stopper.

The 6SN7 is operating fairly linearly and comfortably.
Without Ck bypass, the driver thd reduces, but then overall thd rises
a lot since less even order Dn cancelation takes place.

The fully bypassed Rk on the 6SN7 gives lowish Ra of about 5k for the
paralleled tube
and is thus a sufficiently low enough drive resistance to enhance the
micro detail behaviour of the
2A3, ( very necessary imho to get the best out of not just a triode
output tube,
but ALL output tubes.)

The input tube is 1/2 a 12AU7 of unknown lineage; it measured nicely,
and I like the 12AU7 for inputs; its warm, accurate, and sounds
glorious.

Its Rk is 1.8k, and also bypassed with 470uF, and taken then to 100 ohms
for
the global NFB to be applied.
RL is 50k, 0.47uF to a network for LF gain stepping, 1M+0.033uF
plus 220k, typical in many of my amps to vastly
improve the bass stability when the 12dB of global FB is applied.

The FB resistor divider network is 750 ohms to 100 ohms
with a phase tweaker bypass cap across the 750 ohms = 1,000 pF.
There is a 470pF plus 2.7k zobel network connected from the
driver grid to 0V to control the HF gain and ultimate phase shift of the

12AU7 to 6SN7 interface.
A further 5.6ohms+0.47uF Zobel network is across the OPT secondary,
and finally I got the amp to be fairly ring free when connected to
any value of cap without a pure R load, and when using a square wave.
Open loop BW with all compensation zobels in place was 20Hz to 20kHz,
-3dB,
and with 12 dB of FB the full power BW is 5Hz to 55kHz, 5 ohms.
It remains the same at lower levels of power.

A 5 kHz square wave is a bit ragged due to the mentioned OPT design
simplicity,
but the sine wave response between 30Hz and 20hHz right up to clipping
is dead flat.

A 50k Alps Black pot is used for the gain control.

Input sensitivity with 12dB applied global NFB is 0.7Vrms.
The amp's use with an CD player is fine.
Just no need for any preamp.

The sound is that of a far more powerful amplifier,
with tremendous sense of rightness, instrument detail, warmth without
muddle, not the slightest hint of any lack of bass, the usual beautiful
mids, and detailed top end.

The amp measures well at less than 1% thd at 4 watts into 5 ohms,
mainly all 2H.
But at normal levels of a watt the 3H and other H are present below the
2H
which can be seen on the CRO when monitoring the THD at all levels.
Ro is 0.47 ohm, and although my speakers vary between
4 and 20ohms, the sound appears firm, well timbred, and there isn't any
hint
of the sound being that from an inadequate amplifier.

I played Handel's water music, the sound track of 'The Pianist' for my
tests plus
a not so wonderful Naxos CD, 'The Best of Bach'.

Who says SET amps suck?

Certainly not I!.

Methinks that if the owner wanted more power, he could simply swap the
2A3 for a KT90 since the PT has a 6.3V heater winding, and then
remove the series R I have placed in the B+ lines to trim the B+
to where I want it, and with 270V, and with the UL tap on the
OPT that is provided, maybe 9+ watts of SEUL would be available.

The now unused 1670 OPT UL tap is at 40%.
But it could be at 60%, if you use the plate winding reversed,
thus further drifting a tetrode towards triode, but still not
suffering a huge loss of power due to grid current limitations.

300B could also be used, and with slightly more Ia,
but with the same low Ea, thus suiting moderate power and good matching
to
low value loads, which is a major failing in many SET amps;
they try to match so max power is at 8ohms, but that is
nearly always wrong with modern speakers, and
max power should occur at 3 or 4 ohms.

Patrick Turner.


Whats this I see? Patrick T. using Hammond? Or something brought in by a
customer?


The customer of mine was not prepared to pay for my one-off
trannies, and so he supplied Hammonds for me to use
They turned out OK.

Patrick Turner.





I'm back into sales again. Lots of manual labour on the house this summer as
well. Not much time for tubes.

But if I get time I have a couple of interesting projects in mind. One is a
hybrid. But don't know when.

Cheers, John


  #33   Report Post  
west
 
Posts: n/a
Default

"Patrick Turner" wrote in message
...

John Stewart wrote:

Patrick Turner wrote:


huge snip

Patrick Turner.


Whats this I see? Patrick T. using Hammond? Or something brought in by a
customer?


The customer of mine was not prepared to pay for my one-off
trannies, and so he supplied Hammonds for me to use
They turned out OK.

Patrick Turner.


I'm back into sales again. Lots of manual labour on the house this

summer as
well. Not much time for tubes.

But if I get time I have a couple of interesting projects in mind. One

is a
hybrid. But don't know when.

Cheers, John


Professor, are you using your custom built speakers or a commercial type
with you SE amp? Why is there so little mention at your web site about your
speakers? BTW, John: Nice article you wrote in recent issue of AudioXpress.
Try not to totally abandon the articles. Life is too short. Wow, little ole
me between the Twin Towers of tubes!
west



  #34   Report Post  
Bret Ludwig
 
Posts: n/a
Default


west wrote:


Professor, are you using your custom built speakers or a commercial type
with you SE amp? Why is there so little mention at your web site about your
speakers? BTW, John: Nice article you wrote in recent issue of AudioXpress.
Try not to totally abandon the articles. Life is too short. Wow, little ole
me between the Twin Towers of tubes!
west



It was an okay article but most people want to put some money into a
serious project and not piddle around with cheap transformers if they
are going to spend the time to build one. Best grade OPT's are the way
to go.

  #35   Report Post  
John Stewart
 
Posts: n/a
Default

Bret Ludwig wrote:

west wrote:


Professor, are you using your custom built speakers or a commercial type
with you SE amp? Why is there so little mention at your web site about your
speakers? BTW, John: Nice article you wrote in recent issue of AudioXpress.
Try not to totally abandon the articles. Life is too short. Wow, little ole
me between the Twin Towers of tubes!
west


It was an okay article but most people want to put some money into a
serious project and not piddle around with cheap transformers if they
are going to spend the time to build one. Best grade OPT's are the way
to go.


Be our guest. Author an article for publishing. Amp of your choice.

I will look forward to seeing you in print some day!

JLS



  #36   Report Post  
Patrick Turner
 
Posts: n/a
Default



west wrote:

"Patrick Turner" wrote in message
...

John Stewart wrote:

Patrick Turner wrote:


huge snip

Patrick Turner.

Whats this I see? Patrick T. using Hammond? Or something brought in by a
customer?


The customer of mine was not prepared to pay for my one-off
trannies, and so he supplied Hammonds for me to use
They turned out OK.

Patrick Turner.


I'm back into sales again. Lots of manual labour on the house this

summer as
well. Not much time for tubes.

But if I get time I have a couple of interesting projects in mind. One

is a
hybrid. But don't know when.

Cheers, John


Professor, are you using your custom built speakers or a commercial type
with you SE amp?


The 2A3 amps were a commissioned job for a client who supplied me with tubes and
a set
of Hammond trannies after i told him which ones to get.
I demoed the 2A3 amp to my client using my speakers which are about 88dB/W/M
efficient.
4 watts had a lot of work to do, but we could hear the 2A3 were doing it right,
although not quite as loud as we would like for the speakers on the big
orchestral stuff.
He wanted the 2A3 to drive JBL horn slot tweeters of about 104dB/W/M efficiency.



Why is there so little mention at your web site about your
speakers?


Because they are not my main focus of attention.
IMHO, I think my speakers are second to none; since I have not heard anything
better,
its hard to know how to make improvements.
But trying to sell speakers via the Web has been an utter flop for me.

The prices shown at the website are a bargain, but I can't expect ppl
to agree with that. There are no official magazine reviews which all cost
huge piles of $$$$ that I have not got.
The Audiophile Society of NSW is always very coy about saying how
good/bad ones speakers are in their magazine/website, and you would have had to
have been there
when i demoed my gear.
But all the folks including myself who have demoed gear to such clubs have never
done any good
commercially as a result of driving a truckload of stuff and setting it all up,
and risking damage etc....

If I tried to place my speakers in the local hi-fi shops, they'd
expect 50% commission from the price which would the same as at the website,
which BTW is now
getting quite ancient; 3 years without an update!

Consider a pair of speakers with a price of $4,000 in a hi-fi shop.
I get $2,000 from a sale.
Since such handcrafted speakers take about 4 weeks of work to make and
since the materials cost is about $1,500, then I get only $500 for 4 weeks of
hard slog.
So, damn the shops and their cheap asian junk selling for prices which have no
relation
to the asian labour costs.
95% of speaker sales are determined by a woman who likes small speakers that are

almost invisible.

In 5 years I have had only 2 emails about my speakers.
Its possible to sell an occasional amp via the Web because the people
know tubes make good music, and maybe they realise I have at least some idea
how to go about making an amp.

But I should have started 40 years ago....


Patrick Turner.

  #37   Report Post  
Patrick Turner
 
Posts: n/a
Default



Bret Ludwig wrote:

west wrote:


Professor, are you using your custom built speakers or a commercial type
with you SE amp? Why is there so little mention at your web site about your
speakers? BTW, John: Nice article you wrote in recent issue of AudioXpress.
Try not to totally abandon the articles. Life is too short. Wow, little ole
me between the Twin Towers of tubes!
west


It was an okay article but most people want to put some money into a
serious project and not piddle around with cheap transformers if they
are going to spend the time to build one. Best grade OPT's are the way
to go.


JS likes to perpetuate the idea that anyone who wants to build a tube amp needn't

spend much money on OPTs, and that tube sound is quite a cheap hobby.

This probably appeals to and panders to the hundreds of DIYers of 50yrs old
who dare not spend much more than peanuts on their hobby, lest
they feel they are spending too much, just like a kid of 16 thinking he
mustn't spend too much on the new bicycle rims for the bike he's building, since
hobbies must be cheap,
and affordable, especially if the wife thinks hubbie's soldering efforts are
some crazy thing, and she controls the purse strings.
Meanwhile, although the latter day big kid agonisers over the costs
of OPTs, and whether the extra $1 coupling cap is necessary,
he pays $1,000 per mth on medical insurance, and goodness knows what
on other household expenses.....

For as long as i can remember, kits for all sorts of things in magazines
were about making something that performed barely well enough and for
a fraction of the price of something in a shop.
I have built some kits for frequency measurement, ( impossible with tubes )
and some distortion measurement gear, also based on chips.
But the use of such kits was always lacking in any real ability;
kits are mostly glorified toys, so I then set out to seriously study the details
and
design and build my own distortion testing gear, milivolt meters
with BW from a useful 2Hz to 2Mhz at high Z, and so on.


I applaud JH for devoting his time to those he caters for.
He helps keep good men from going bad in a pub, and it generally fosters
interest in tubecraft.

They will mostly never buy the Real Mcoy item that has correct weight OPTs and
has been designed to a standard, not down to a price, and after wrestling with
getting their amp going, most will turn to some other interest later.....

Maybe 2% of the ppl that take up tubecraft as a result of the lead John has given
them will
go on to become a little more fanatic about it all and begin to think seriously
for themselves
about their audio constructions, guided by what they hear, and see on a CRO.


Patrick Turner.




  #38   Report Post  
Jon Yaeger
 
Posts: n/a
Default

I've got an idea that probably won't fly, but here goes.

You've got to give John a lot of credit for his many contributions to
tubecraft. I don't know of anyone who is more productive, both in writing
and designing stuff that actually works.

So I propose that in appreciation, we R.A.T.s take up a collection of stuff
that we think might make a good amp, and send it to John to do a "R.A.T.
Sponsored Design."

That would accomplish a couple of things, including make other folks aware
of the R.A.T. newsgroup who are more interested in arguing about tubes
instead of Jesus and global warming.

Count me in for an enclosure. Hey Patrick, how about some OPT iron??

Jon




in article , Patrick Turner at
wrote on 9/29/05 8:20 AM:



Bret Ludwig wrote:

west wrote:


Professor, are you using your custom built speakers or a commercial type
with you SE amp? Why is there so little mention at your web site about your
speakers? BTW, John: Nice article you wrote in recent issue of AudioXpress.
Try not to totally abandon the articles. Life is too short. Wow, little ole
me between the Twin Towers of tubes!
west


It was an okay article but most people want to put some money into a
serious project and not piddle around with cheap transformers if they
are going to spend the time to build one. Best grade OPT's are the way
to go.


JS likes to perpetuate the idea that anyone who wants to build a tube amp
needn't

spend much money on OPTs, and that tube sound is quite a cheap hobby.

This probably appeals to and panders to the hundreds of DIYers of 50yrs old
who dare not spend much more than peanuts on their hobby, lest
they feel they are spending too much, just like a kid of 16 thinking he
mustn't spend too much on the new bicycle rims for the bike he's building,
since
hobbies must be cheap,
and affordable, especially if the wife thinks hubbie's soldering efforts are
some crazy thing, and she controls the purse strings.
Meanwhile, although the latter day big kid agonisers over the costs
of OPTs, and whether the extra $1 coupling cap is necessary,
he pays $1,000 per mth on medical insurance, and goodness knows what
on other household expenses.....

For as long as i can remember, kits for all sorts of things in magazines
were about making something that performed barely well enough and for
a fraction of the price of something in a shop.
I have built some kits for frequency measurement, ( impossible with tubes )
and some distortion measurement gear, also based on chips.
But the use of such kits was always lacking in any real ability;
kits are mostly glorified toys, so I then set out to seriously study the
details
and
design and build my own distortion testing gear, milivolt meters
with BW from a useful 2Hz to 2Mhz at high Z, and so on.


I applaud JH for devoting his time to those he caters for.
He helps keep good men from going bad in a pub, and it generally fosters
interest in tubecraft.

They will mostly never buy the Real Mcoy item that has correct weight OPTs and
has been designed to a standard, not down to a price, and after wrestling with
getting their amp going, most will turn to some other interest later.....

Maybe 2% of the ppl that take up tubecraft as a result of the lead John has
given
them will
go on to become a little more fanatic about it all and begin to think
seriously
for themselves
about their audio constructions, guided by what they hear, and see on a CRO.


Patrick Turner.





  #39   Report Post  
Patrick Turner
 
Posts: n/a
Default



Jon Yaeger wrote:

I've got an idea that probably won't fly, but here goes.

You've got to give John a lot of credit for his many contributions to
tubecraft. I don't know of anyone who is more productive, both in writing
and designing stuff that actually works.

So I propose that in appreciation, we R.A.T.s take up a collection of stuff
that we think might make a good amp, and send it to John to do a "R.A.T.
Sponsored Design."

That would accomplish a couple of things, including make other folks aware
of the R.A.T. newsgroup who are more interested in arguing about tubes
instead of Jesus and global warming.

Count me in for an enclosure. Hey Patrick, how about some OPT iron??


There are a bunch of fully worked out designs at my website.

Also a couple of samples of OPT that anyone can wind.

I had hoped someone would have addopted my design and wound a quantity to sell back
to me
but not even the dumb chinese were able to work out what i have at my site.
But several amateur audio ppl persevered to wind my OPT No1, and got good results.

How does one define a real audio tube crafter? One who winds his OPTs,
chokes, PTs, crossovers, and makes his chassis, and works out the whole design from
first principles.
Not many of thse ppl around anymore, either they have got old, or are too short
of time or enthusiasm.


Audio Express may not want to direct ppl to rec.audio.tubes or form any association
with us.
I am sure they'd prefer readers to stay dependant on buying the magazine.
Forums on the web allow ppl the luxury of talking to blokes who have been through
all the problems before their turn comes along, so they don't even need to buy
copies of AE.

I used to write long articles for the news letter of an audio club based in Sydney.
Membership was about 100 members, and only about 3 blokes understood anything I
said.
Having an active presence in an audio club proved quite useless to my business,
and they only wanted amps if they were priced next to nothing.
I am no longer a member of any audio clubs, and i am sure they know where I am,
and if they wanted to follow along with the sensible discussions here I am sure they

could have, but NOT ONE HAS out of two clubs with a total membership of
over 200 over the last 5 years.
Tube gear ownership amoungst all these audiophiles is way above the national
average,
and DIYing is fairly active, but methinks they don't like me much because I know
more than they do, and i have a completely methodical approach; no guessing, and
not much adherence to audio myths, and I don't endorse BS.

I could be wrong about all Audio Express; but you'd think AE ppl would have
perhaps contributed to discussions here but perhaps they think that the public
newsgroups are a sewer
of crappy chatter, and have stayed well away, like so many have,
because they are genteel ppl who don't like being set upon by the mad dogs
that lurk here.

The world wide web provides ppl like myself to stay sharp with tube craft
in an active forum. I am not shy about pitting my wits
against the best and the worst here, and Its a damn sight more rewarding
than posting to newsletters of audio clubs, and never ever getting any response,
and I enjoy complete editorial freedom here which is preferable to the
crap that I have seen go on in some audio mags when people who make amps have had
feature
articles done on their gear.

I established a website to encompass all I really need to say;
if anyone wants to know more they only have to email me.
The only exception is Phil Allison, who knows his emails get deleted with spam,
and his phone calls terminated.
I don't take **** from nobody, but I have helped maybe
hundreds with their problems.

I hope you follow my salient thoughts about amp building
and the prosletizing of tubecraft.

The interactive nature of the web and its active helpful contributors
is priceless; to real thinkers, magazines may not have the prominence
they used to; they are a media of the past.

Patrick Turner.






Jon

in article , Patrick Turner at
wrote on 9/29/05 8:20 AM:



Bret Ludwig wrote:

west wrote:


Professor, are you using your custom built speakers or a commercial type
with you SE amp? Why is there so little mention at your web site about your
speakers? BTW, John: Nice article you wrote in recent issue of AudioXpress.
Try not to totally abandon the articles. Life is too short. Wow, little ole
me between the Twin Towers of tubes!
west

It was an okay article but most people want to put some money into a
serious project and not piddle around with cheap transformers if they
are going to spend the time to build one. Best grade OPT's are the way
to go.


JS likes to perpetuate the idea that anyone who wants to build a tube amp
needn't

spend much money on OPTs, and that tube sound is quite a cheap hobby.

This probably appeals to and panders to the hundreds of DIYers of 50yrs old
who dare not spend much more than peanuts on their hobby, lest
they feel they are spending too much, just like a kid of 16 thinking he
mustn't spend too much on the new bicycle rims for the bike he's building,
since
hobbies must be cheap,
and affordable, especially if the wife thinks hubbie's soldering efforts are
some crazy thing, and she controls the purse strings.
Meanwhile, although the latter day big kid agonisers over the costs
of OPTs, and whether the extra $1 coupling cap is necessary,
he pays $1,000 per mth on medical insurance, and goodness knows what
on other household expenses.....

For as long as i can remember, kits for all sorts of things in magazines
were about making something that performed barely well enough and for
a fraction of the price of something in a shop.
I have built some kits for frequency measurement, ( impossible with tubes )
and some distortion measurement gear, also based on chips.
But the use of such kits was always lacking in any real ability;
kits are mostly glorified toys, so I then set out to seriously study the
details
and
design and build my own distortion testing gear, milivolt meters
with BW from a useful 2Hz to 2Mhz at high Z, and so on.


I applaud JH for devoting his time to those he caters for.
He helps keep good men from going bad in a pub, and it generally fosters
interest in tubecraft.

They will mostly never buy the Real Mcoy item that has correct weight OPTs and
has been designed to a standard, not down to a price, and after wrestling with
getting their amp going, most will turn to some other interest later.....

Maybe 2% of the ppl that take up tubecraft as a result of the lead John has
given
them will
go on to become a little more fanatic about it all and begin to think
seriously
for themselves
about their audio constructions, guided by what they hear, and see on a CRO.


Patrick Turner.





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