[Raymond Koonce]

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Regards,

Raymond

[Bob H.]

Hi Raymond

Nice looking amp. The available tube supply won't dry up anytime soon
for it.

Did you measure the amount of nfb you found preferable in triode mode?

Thanks,
Bob H.


Raymond Koonce wrote:
Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Regards,

Raymond

[Ian Iveson]

Raymond Koonce wrote

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Beautiful job.

How are the sides fixed to the copper?

Is the base flange formed by folding?

What kind of laquer did you use for the copper? Did you consider other
finishes, such as plating or verdigris?

What switch did you use for the attenuator?

cheers, Ian

[Andre Jute]

Raymond Koonce wrote:
Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Regards,

Raymond

Ooh, so nice, Raymond. What did you lacquer the copper with?

Andre Jute

[Andre Jute]

Raymond Koonce wrote:
Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Regards,

Raymond

Ooh, so nice, Raymond, and a different tube too. What did you lacquer
the copper with?

Andre Jute

[Peter Wieck]

Raymond Koonce wrote:
Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

Out of curiosity, why Mercury Rectifiers? It has been my experience
that they can be quite noisy as compared to more typical choices.

Thanks in advance.

Peter Wieck
Wyncote, PA

[Raymond Koonce]

Thanks Bob,

The 816s are a little hard to find at decent prices, but I have a few on
hand. They'll probably last a long time the way I'm running them.

I haven't measured the nfb. The amp is a little hard to test because I
can't run it upside down due to the 816s. I had to solder in a buch of
wires to various nodes I wanted to test and run them to a barrier strip
screwed to my bench. It worked OK, but was a little tedious.

BR,

Raymond

Bob H. wrote:

Hi Raymond

Nice looking amp. The available tube supply won't dry up anytime soon
for it.

Did you measure the amount of nfb you found preferable in triode mode?

Thanks,
Bob H.


Raymond Koonce wrote:

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Regards,

Raymond

[Raymond Koonce]

Ian Iveson wrote:

Raymond Koonce wrote


Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?


Beautiful job.

How are the sides fixed to the copper?

Is the base flange formed by folding?

What kind of laquer did you use for the copper? Did you consider other
finishes, such as plating or verdigris?

What switch did you use for the attenuator?

cheers, Ian


Hi Ian,

The mahogany is bolted with four long brass rods running in the corners
of the chassis and threaded on each end.

Yes, the base flange was folded under by the sheet metal shop on their
brake.

I used clear lacquer that I bought at Home Depot in spray cans. I
really didn't consider anything else because I wanted the look of the
copper.

The attenuator is a 100K version that I bought from a guy in Taiwan via
ebay for about $60. It is very well-made.

Best regards,

Raymond

[Raymond Koonce]

Andre Jute wrote:

Raymond Koonce wrote:

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Regards,

Raymond


Ooh, so nice, Raymond, and a different tube too. What did you lacquer
the copper with?

Andre Jute


Hi Andre,

I used clear lacquer from Home Depot. Cheap and effective. About 4
coats over the polished copper and then one more over the silk screening.

BR,

Raymond

[Raymond Koonce]

Peter Wieck wrote:

Raymond Koonce wrote:

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.


Out of curiosity, why Mercury Rectifiers? It has been my experience
that they can be quite noisy as compared to more typical choices.

Thanks in advance.

Peter Wieck
Wyncote, PA


I've used them before and haven't had a noise problem. I like the look.

Raymond

[Peter Wieck]

Raymond Koonce wrote:

I've used them before and haven't had a noise problem. I like the look.

Good enough. Thanks.

Peter Wieck
Wyncote, PA

[Joseph Meditz]

Raymond Koonce wrote:
Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Regards,

Raymond

It sure is pretty! I then looked at your other amps which are also
very beautiful especially with that red powder coat.

How did you do the silk screening? Is there an amateur kit available?

Joe

[Mikkel C. Simonsen]

Raymond Koonce wrote:

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Looks great - as usual

Best regards,

Mikkel C. Simonsen

[Iain Churches]

"Raymond Koonce" wrote in message
...
Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?


Hello Raymond.

Congratulations, a beautiful job:-)
I would be interested to know the level of feedback you
finally arrive at, and also the output impedance too.

Do you have any performance figs?

I am just taking my first steps in SET after being
very impressed indeed with a Russian built Resnekov
SET owned by a professional cellist that I know.

Iain

[Doug]

Raymond Koonce wrote:
Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Regards,

Raymond

What a beautiful piece of work Raymond...real craftsmanship!

Best regards : Doug Bannard

[Raymond Koonce]

Joseph Meditz wrote:

Raymond Koonce wrote:

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Regards,

Raymond


It sure is pretty! I then looked at your other amps which are also
very beautiful especially with that red powder coat.

How did you do the silk screening? Is there an amateur kit available?

Joe


Hi Joe,

Thanks! I sure like building these things. Everybody like the red color.

The silk screening is not too hard, but it's hard to find information.
Here's the process I used:

You can see the graph paper I used for layout purposes. I took scans of
the layout paper and inserted them into a vector drawing program as a
layer. On another layer I did the artwork and then removed the scans.
I printed a positive of remaining artwork layer on our large format
plotter at work on clear film.

The next part required a little practice. I bought some silk screening
supplies from a place in Maine which I found on the internet. I bought
from them because the salesman was helpful and they had what I needed.
I bought a screen of the appropriate size already stretched in a wood
frame. The photo emulsion comes in two parts which are mixed and poured
onto the screen. Push it into the mesh with a rubber squeegy. Tip:
get a squeegy that fits the frame. It's easier to get an even layer.
Let the emulsion dry overnight in a completely dark area. I covered
mine in a cardboard container.

Next step is the exposure. There's a chart that comes with the emulsion
that gives exposure times with different types of light. I used a 150
watt clear incandescent in an aluminum reflector. IIRC, it was mounted
17" above the screen. The screen is laid upside down over a black cloth
to avoid reflections and the artwork is laid over that, ink side down,
so you see the artwork in reverse. Lay a sheet of clear glass over the
artwork to hold it tight against the screen. Expose the screen to the
light for about 1.5 hours. When you remove the artwork, mist the screen
with clear water and the unexposed areas under the artwork will start to
dissolve. Immediately take the screen outdoors and spray it with your
water hose at high pressure. The unexposed emulsion washes out, leaving
the screen mesh for the ink to go through.

Align the screen over the work, pour a little ink into the frame and
squeegy it over the work. 10 seconds and it's done. Lift it carefully
and let the ink dry overnight. I sprayed a clear lacquer over the ink
for protection.

It's really easier than it sounds here and for $75 I got the screen,
some tools and enough emulsion to do 1000 amps.

Best regards,

Raymond

[Raymond Koonce]

Iain Churches wrote:

"Raymond Koonce" wrote in message
...

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?



Hello Raymond.

Congratulations, a beautiful job:-)
I would be interested to know the level of feedback you
finally arrive at, and also the output impedance too.

Do you have any performance figs?

I am just taking my first steps in SET after being
very impressed indeed with a Russian built Resnekov
SET owned by a professional cellist that I know.

Iain


Hello Iain,

Thanks :-) I sure enjoyed building this amp.

I don't have any performance specs except for the output power, about
2.7 WPC in pentode, less in triode. I have no idea how to calculate the
amount of feedback. Tips?

I think you 'll be impressed with a properly built triode amp. I put my
McIntosh amps away after I built my first triode amp, a 45 SE stereo.

Best regards,

Raymond

[Patrick Turner]

"Mikkel C. Simonsen" wrote:

Raymond Koonce wrote:

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Looks great - as usual

Best regards,

Mikkel C. Simonsen

The specs indicate 1.5mV of hum.

In horn speakers with 100dB/W/M that 1.5mV would plainly be audible
if the horns were that sensitive at 100Hz, and the hum was 100Hz hum.

Has any attempt been made to reduce the hum?

Patrick Turner.

[Raymond Koonce]

Patrick Turner wrote:


"Mikkel C. Simonsen" wrote:

Raymond Koonce wrote:

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Looks great - as usual

Best regards,

Mikkel C. Simonsen


The specs indicate 1.5mV of hum.

In horn speakers with 100dB/W/M that 1.5mV would plainly be audible
if the horns were that sensitive at 100Hz, and the hum was 100Hz hum.

Has any attempt been made to reduce the hum?

Patrick Turner.

Hi Patrick,

My speakers are fairly sensitive, Klipsch Cornwalls, rated 101dB/W/M.
The hum (60 Hz probably from filaments) is not audible to my 50+ year
ears from closer than a normal listening distance. If I stick my ear in
the woofer, I can hear some, but it's not objectionable. I am running
my 47 filaments on AC with hum pots and all I've done is to adjust the
hum pots to the lowest AC at the speaker terminals.

My PSU is LCLCRC and is very quiet, no 120Hz hum at all.

Suggestions?

Best,

Raymond

[John Byrns]

In article ,
Patrick Turner wrote:

"Mikkel C. Simonsen" wrote:

Raymond Koonce wrote:

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Looks great - as usual

Best regards,

Mikkel C. Simonsen

The specs indicate 1.5mV of hum.

In horn speakers with 100dB/W/M that 1.5mV would plainly be audible
if the horns were that sensitive at 100Hz, and the hum was 100Hz hum.

Has any attempt been made to reduce the hum?

Patrick Turner.

I agree, 1.5 mV of hum is way too much and easily audible even on
speakers of moderate efficiency. I shoot for a hum level 80 dB below 1
Watt without feedback, which translates to about 0.3 mV into 8 Ohms.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[John Byrns]

In article ,
Raymond Koonce wrote:

Patrick Turner wrote:


"Mikkel C. Simonsen" wrote:

Raymond Koonce wrote:

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Looks great - as usual

Best regards,

Mikkel C. Simonsen


The specs indicate 1.5mV of hum.

In horn speakers with 100dB/W/M that 1.5mV would plainly be audible
if the horns were that sensitive at 100Hz, and the hum was 100Hz hum.

Has any attempt been made to reduce the hum?

Patrick Turner.

Hi Patrick,

My speakers are fairly sensitive, Klipsch Cornwalls, rated 101dB/W/M.
The hum (60 Hz probably from filaments) is not audible to my 50+ year
ears from closer than a normal listening distance. If I stick my ear in
the woofer, I can hear some, but it's not objectionable. I am running
my 47 filaments on AC with hum pots and all I've done is to adjust the
hum pots to the lowest AC at the speaker terminals.

My PSU is LCLCRC and is very quiet, no 120Hz hum at all.

Doesn't a correctly adjusted filament "hum pot" cancel the 60 Hz
component of hum caused by the filament, leaving only 120 Hz hum, and
higher harmonics, due to the filament?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[Patrick Turner]

Raymond Koonce wrote:

Patrick Turner wrote:


"Mikkel C. Simonsen" wrote:

Raymond Koonce wrote:

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Looks great - as usual

Best regards,

Mikkel C. Simonsen


The specs indicate 1.5mV of hum.

In horn speakers with 100dB/W/M that 1.5mV would plainly be audible
if the horns were that sensitive at 100Hz, and the hum was 100Hz hum.

Has any attempt been made to reduce the hum?

Patrick Turner.

Hi Patrick,

My speakers are fairly sensitive, Klipsch Cornwalls, rated 101dB/W/M.
The hum (60 Hz probably from filaments) is not audible to my 50+ year
ears from closer than a normal listening distance. If I stick my ear in
the woofer, I can hear some, but it's not objectionable. I am running
my 47 filaments on AC with hum pots and all I've done is to adjust the
hum pots to the lowest AC at the speaker terminals.

My PSU is LCLCRC and is very quiet, no 120Hz hum at all.

Suggestions?

Best,

Raymond

A guy here built a pair of tratrix profile horns with Fostex full range
drivers
and the result was high sensitivity and horrible sound, as though it was
fighting its way out
of a wooden box.
He tried his own generic SS amps which didn't make any difference, then
my class AB triode amp
using PP 6CM5 in triode, and that made no difference either; the main
problem wasn't the amp,
it seldom is, it was with the speakers.
But my triode amp was at that time silent with normal speakers because
hum was just below 1mV.
But it was clearly and anoyingly loud with these horns, and if any amp
has power supply switching noise
creeping in somehow from the diodes, and this is very common, then you
will hear
a buzz of some sort with horns.

If the sole harmonic component of the hum is 60Hz, then it will not be
as noticeable as 120Hz or
180, 240, 300Hz etc, because as F rises above say 20Hz the noticeablity
to our ears increases.

Anyway, My triode AB amp hum became noticeable and I was forced to
improve the B+ filtering
by making alterations to the regulated B+ supply; it has regulation
rather than CLC.
Having made this alteration the hum became much lower by about 12dB, and
I can only assume its noticeablity with horn speakers was
reduced to below audibility; it was not re-tried again with horns.

Any amplifier with a low amount of NFB is especially prone to having
some noise at its output
even with the input grounded.

NFB generated within the amp circuit enclosed by NFB which would include
any heater leakage from filaments to
cathode, or any unbalanced/uncancelled heater voltages across any dh
cathodes is all reduced by the NFB
in a similar way as the THD/IMD etc is reduced by NFB, so if there is
say 3mV of hum before any FB is applied,
then 20dB of NFB reduces that hum to 0.3mV, a respectanble figure for
any power amp.

If a tube amp is run without any loop NFB, and hum from heating
filaments or dh cathodes is the culprit, then
one answer is to use well filitered floating dc supplies for all and
ground these supplies well to 0V
with large electrolytics, which is easy because with low dc cathode
voltages involved,
a 470uF rated at 10 to 63V isn't a large cumbersome item.

Needless to say, SE amps need good CLC filtered anode supplies to the
output and driver stages.

But usually dc applied carefully around cathode circuits and anode
circuits should reduce
hums and buzzes to neglifible levels. I say should, and sometimes the
amp is still noisy
with well smoothed supplies.
Then is a case of revising earth paths, reducing magnetic induction and
reducing
stray capacitances until noise is minimized. This is most difficult to
achieve if the PS is on the same chassis as the
amp. But not impossible, and sometimes some trial and error with leads
and item positions
need to be done with a CRO connected to confirm any noise reductions
that are achieved.
Eventually one learns never to have critical leads running under power
trannies, and that no ferrous chassis
like copper and Al and brass are worst for magnetic bothers, and that
screening cables only works against
electrostatic stray C noise pick up.
One star earthing point is a must, located near the input.
The chassis should be grounded directly to the earth lead of the 3 wire
mains input lead,
and it also should then connect to a 0V buss by say 22 ohms, so that
preamps and the like
don't form earth loops.
If it is impossible to have all DC heating, then the AC heating should
have an adjustable
hum balance pot; a wire wound 250 ohm pot across the 6.3V with wiper
grounded or taken to the
R&C cathode bias network will allow hum adjustments.

Patrick Turner.

[Raymond Koonce]

John Byrns wrote:
In article ,
Patrick Turner wrote:


"Mikkel C. Simonsen" wrote:

Raymond Koonce wrote:

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Looks great - as usual

Best regards,

Mikkel C. Simonsen

The specs indicate 1.5mV of hum.

In horn speakers with 100dB/W/M that 1.5mV would plainly be audible
if the horns were that sensitive at 100Hz, and the hum was 100Hz hum.

Has any attempt been made to reduce the hum?

Patrick Turner.


I agree, 1.5 mV of hum is way too much and easily audible even on
speakers of moderate efficiency. I shoot for a hum level 80 dB below 1
Watt without feedback, which translates to about 0.3 mV into 8 Ohms.


Regards,

John Byrns

Hi John,

Maybe I'm measuring something wrong here, but I honestly can't hear the
hum from 2 feet away from the speakers. I don't have a sensitive AC
voltmeter, just a regular digital VOM. I adjust my hum pots to minimum
AC voltage on the speaker terminals. That's worked OK for me on my 300B
amps. I've found that the higher the filament voltage, the harder it is
to tame the hum. 47s are pretty easy at 2.5V.

Best regards,

Raymond

[Raymond Koonce]

John Byrns wrote:

In article ,
Raymond Koonce wrote:


Patrick Turner wrote:


"Mikkel C. Simonsen" wrote:


Raymond Koonce wrote:


Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?

Looks great - as usual

Best regards,

Mikkel C. Simonsen


The specs indicate 1.5mV of hum.

In horn speakers with 100dB/W/M that 1.5mV would plainly be audible
if the horns were that sensitive at 100Hz, and the hum was 100Hz hum.

Has any attempt been made to reduce the hum?

Patrick Turner.

Hi Patrick,

My speakers are fairly sensitive, Klipsch Cornwalls, rated 101dB/W/M.
The hum (60 Hz probably from filaments) is not audible to my 50+ year
ears from closer than a normal listening distance. If I stick my ear in
the woofer, I can hear some, but it's not objectionable. I am running
my 47 filaments on AC with hum pots and all I've done is to adjust the
hum pots to the lowest AC at the speaker terminals.

My PSU is LCLCRC and is very quiet, no 120Hz hum at all.


Doesn't a correctly adjusted filament "hum pot" cancel the 60 Hz
component of hum caused by the filament, leaving only 120 Hz hum, and
higher harmonics, due to the filament?


Regards,

John Byrns


Hi again John,

Yes, you're correct. Thanx.

Raymond

[Raymond Koonce]

Bret Ludwig wrote:

Raymond Koonce wrote:



Hello Raymond.

Congratulations, a beautiful job:-)
I would be interested to know the level of feedback you
finally arrive at, and also the output impedance too.

Do you have any performance figs?

I am just taking my first steps in SET after being
very impressed indeed with a Russian built Resnekov
SET owned by a professional cellist that I know.

Iain



Hello Iain,

Thanks :-) I sure enjoyed building this amp.

I don't have any performance specs except for the output power, about
2.7 WPC in pentode, less in triode. I have no idea how to calculate the
amount of feedback. Tips?

I think you 'll be impressed with a properly built triode amp. I put my
McIntosh amps away after I built my first triode amp, a 45 SE stereo.



Extensive listening to other people's single ended amps is what
convinced me that overall, the worst McIntosh amp beats any single
ended amp. Unless you want Fender Champ full bodied grunge, in which
case, run your CD player through a couple of Fender Champs.


Sorry, I don't feed trolls.

[Iain Churches]

"John Byrns" wrote in message
...
In article ,
Patrick Turner wrote:


The specs indicate 1.5mV of hum.

In horn speakers with 100dB/W/M that 1.5mV would plainly be audible
if the horns were that sensitive at 100Hz, and the hum was 100Hz hum.

Has any attempt been made to reduce the hum?

Patrick Turner.

I agree, 1.5 mV of hum is way too much and easily audible even on
speakers of moderate efficiency. I shoot for a hum level 80 dB below 1
Watt without feedback, which translates to about 0.3 mV into 8 Ohms.


Regards,

John Byrns


My 50W amp measured wideband has 300µV of noise including hum
I did not "shoot at it" I was lucky, it just came out that way:-))

Thanks John, the info which you and Patrick have provided in this
thread is of great interest.

Regards to all
Iain

[Iain Churches]

"Raymond Koonce" wrote in message
news


Iain Churches wrote:

"Raymond Koonce" wrote in message
...

Hi RATs,

Here's a link to a project I've had on the bench for a while and got
finished today. I learned quite a bit on this one.

http://www.timebanditaudio.com/47%20Amp/Carmen47.html

It sounds as good as it looks.

Comments, questions?



Hello Raymond.

Congratulations, a beautiful job:-)
I would be interested to know the level of feedback you
finally arrive at, and also the output impedance too.

Do you have any performance figs?

I am just taking my first steps in SET after being
very impressed indeed with a Russian built Resnekov
SET owned by a professional cellist that I know.

Thanks :-) I sure enjoyed building this amp.

I don't have any performance specs except for the output power, about 2.7
WPC in pentode, less in triode. I have no idea how to calculate the
amount of feedback. Tips?


Hi Raymond.
It is so refreshing to see a thread on RAT
by someone who has actually *built* something
(and makes such a nice contrast to the voluminous
posts from some of those whose presence here
is an enigma - their sole purpose seems to be to
pour derision on thermionic audio)

This is a sad state of affairs, because it keeps
away so many good people who have an interest in
tube audio but their lack of knowledge and
experience prevents them from posting here for
fear of ridicule.

I have a simple method for measuring the feedback.
Firstly with a standard 8 Ohm (50W) dummy load
connected I disconnect the feedback loop with the
level of the source generator low. I then increase
the level to give me a reasonable output level across
the 8 Ohm Load. You can use any value you choose
I use 8.94V which equates to 10W (V2/R)
Call this V1.

Then I switch off the amp, and reconnect the
feedback loop. Power up again, and with the
source at the same level measure the output
voltage again. Call this new value V2.

Using the formula 20log(V1/V2) you can
work out the feedback in dB.So if you get
8.94V open loop and 4.47V closed loop
then you have 6dB of feedback.

Easy and fun:-)

I think you 'll be impressed with a properly built triode amp. I put my
McIntosh amps away after I built my first triode amp, a 45 SE stereo.

Yes. My only regret is that it has taken me so
long to become interested in SET. I would be
interested to know more about the 45 SE
which you build.

Congratulations once again on a fine project:-)
Iain

[Raymond Koonce]

Iain Churches wrote:
snip

Hello Raymond.

Congratulations, a beautiful job:-)
I would be interested to know the level of feedback you
finally arrive at, and also the output impedance too.

Do you have any performance figs?

I am just taking my first steps in SET after being
very impressed indeed with a Russian built Resnekov
SET owned by a professional cellist that I know.


Thanks :-) I sure enjoyed building this amp.

I don't have any performance specs except for the output power, about 2.7
WPC in pentode, less in triode. I have no idea how to calculate the
amount of feedback. Tips?



Hi Raymond.
It is so refreshing to see a thread on RAT
by someone who has actually *built* something
(and makes such a nice contrast to the voluminous
posts from some of those whose presence here
is an enigma - their sole purpose seems to be to
pour derision on thermionic audio)

Let 'em pour! I have a thick flame suit :-)

This is a sad state of affairs, because it keeps
away so many good people who have an interest in
tube audio but their lack of knowledge and
experience prevents them from posting here for
fear of ridicule.

I agree wholeheartedly. I learned a lot from RAT when I first started
building amps. Lately it seems there's not much left here.

I have a simple method for measuring the feedback.
Firstly with a standard 8 Ohm (50W) dummy load
connected I disconnect the feedback loop with the
level of the source generator low. I then increase
the level to give me a reasonable output level across
the 8 Ohm Load. You can use any value you choose
I use 8.94V which equates to 10W (V2/R)
Call this V1.

:-) I'll never get to 10W with a single 47. But I get the idea.


Then I switch off the amp, and reconnect the
feedback loop. Power up again, and with the
source at the same level measure the output
voltage again. Call this new value V2.

I built this amp with variable feedback via a rotary switch. I use four
resistors per side, IIRC, 4.7K, 2.2K, 1K, 400 ohms.

Using the formula 20log(V1/V2) you can
work out the feedback in dB.So if you get
8.94V open loop and 4.47V closed loop
then you have 6dB of feedback.

I'll have the amp back on the bench next week to rewire my volume
control. Naturally, I wired it backwards :-)

Easy and fun:-)


I think you 'll be impressed with a properly built triode amp. I put my
McIntosh amps away after I built my first triode amp, a 45 SE stereo.


Yes. My only regret is that it has taken me so
long to become interested in SET. I would be
interested to know more about the 45 SE
which you build.

The 45 amp I built (along with several 2A3 versions) is based on the
Simple 45 circuit from Joseph Esmilla, JELabs. It's really simple, low
parts count and it sounds great, although it does only 1.5 watts.

Congratulations once again on a fine project:-)
Iain

Thanks much Iain,

Best regards,

Raymond