Trevor Wilson wrote:
"Iain Churches" wrote in message
i.fi...
"Trevor Wilson" wrote in message
...
"Iain Churches" wrote in message
i.fi...
"Trevor Wilson" wrote in message
...
"Iain Churches" wrote in message
i.fi...
"Trevor Wilson" wrote in message
...
A SET amplifier rated at (say) 10 Watts @ 8 Ohms, can only deliver a
maximum of 5 Watts, when the impedance falls to 4 Ohms, 2.5 Watts @ 2
Ohms
and so on.
Trevor, you are going round in circles. Please study
IEC/EN/BS EN 60268-5 to which most
competent loudspeakers confirm.
The exception being ESL.
**ESLs ARE competent loudspeakers.
No one suggested they were not. They are the
common exception to IEC/EN/BS EN 60268-5.
When asked about this, Russ Walker smiled and
said that he belived his father Peter had "received
a dispensation from the Pope"
That satisfied everyone:-)
**Except SET owners, of course. SET amps will have problems in coping
with
what is widely acknowledged as the most accurate form of music
reproduction system. Seems like a bad trade-off to me.
I recall a post from Patrick just a couple of days ago,
in which he states that a good SET amp has no difficulty
in driving an ELS. I would presume he says that from
first-hand experience.
**AFTER Patrick submits a frequency response, I'll get interested.
In a recent other post most people have ignored because it probably is
too hard to refute,
I mentioned Quad-II and ESL57. There isn't any need for ME to posr a
response curve
when if you wanted one you could find one done by Walker & Co.
get it from the horses mouth, not me.
SE amps that I make have Rout of less than Walker's amps, so whatever
Walker got when he measured the response
would be flatter if my amps were used, except I suspect ESL57 sounds a
little treble rich if driven by
an amp with a say Rout = 0.1 ohm.
I do not,
nor have I ever, suggested that a SET cannot make an ESL produce sound. What
I do dispute, is the ability of a SET amp to drive most ESLs such that they
provide a linear frequency response.
Depends what SET amp you are talking about. They vary considerably in
their Rout
depending on the whims of the designers.
Some SET amps will not give a linear F response because Rout exceeds the
ESL maker's specifaction
of source R in order to get a flat voltage response of say +/- 1.0dB.
Some SET amps will easily produce a response within the +/- 1.0dB 20Hz
to 20kHz,
simply because their Rout is say 0.3 ohms, and the lowest Z of the ESL
along the band at some HF
has a minimum of say 2 ohms.
IOW: Drive an ESL with a SET amp and
you will probably get sound. With the SETs Patrick mentioned, you may even
get quite acceptable sound (at huge cost).
Yes, finally you have got the message that not all SET amps are the
same,
and ppl find the sound they hear worth the expense.
If that SET is compared with
another amplifier, which possesses a suitably low output impedance and high
current ability, then the sound from the ESLs will mostly likely be far more
accurate.
Not necessarily so. Its not hard to make an SE amp with sufficient
voltage and current ability
so much so that it acts like a Rolls Royce, and you never have to worry
about having enough
power; there is always enough. And the Rout of the amp need only be
sufficiently low
to meet the speaker maker's recomendations. Very little is to be gained
sonically
by exceeding the maker's requirements which are usually based on basic
LCR theory.
Put it this way, all my amps have Rout less than 1 ohm, often only 0.3
ohms,
including all SE and PP tube and SS PP amps.
Forcing any of my designs to have lower Rout by using more gainy tubes
and more GNFB
will not improove the sonics. The Law of diminishing returns sets in.
Back in the days when I used SE amplifiers, I thought they sounded
pretty good. Great, in fact.
1958 was it? maybe a lone 6V6? Yeah, i went through all that too at
about that time.
The first serious SE amps I did in 1993 used 1 x EL84/6BQ5 in pentode
with local cathode FB from the
OPT and as I added GNFB the sound became clearer and better up to a
point where
any further increase was useless. The stereo amps are still in my shed
on a Kriesler
radio chassis.
I ran a pair of sensitive "ceiling speakers" with "full range" ability,
ie
about 50Hz to 18kHz in ported boxes and because of good sensitivity the
little SE amps did a fine job for some radio music. I used a walkman to
provide
the FM radio feed.
With any class A pentode/beam tet amp, a total of 20dB of series voltage
NFB is all you need
to make what is virtually a current source into virtually a voltage
source.
Triode SET amps have local NFB within the output tube, so Ra is usually
10 times lower compared to pentodes/beams.
So you simply do not need to apply much GNFB.
The 845 SET amps have only 8 dB GNFB.
Then I built a push pull amp and my world
changed. Simply no comparison. The push pull amp was more powerful, able to
cope with a wide range of load impedances, lower distortion, etc, etc. For
the record: Both SE amp push pull amps used 6V6 output valves. I was 16
years old.
So I guessed right about what you and countless others have done.
I have not bothered with SE designs since.
Nobody is forcing you towards anything. But because YOU
have not bothered with SE, it does not make it wrong that anyone else
might
persevere with SE designs.
The amp with four 6V6 in SE parallel beam tetrode with local NFB from
the OPT
and some GNFB will give you 20 watts of PURE CLASS A,
and the pair you used in PP was maybe barely capable of the 20 watts,
more like only 12 watts, and very class AB, and lots more odd order THD
than the SE.
The first few watts of the SE amp will easily sound just as good or
better than the
PP amp.
Tonight I demonstrated one of the 50 watt 845 amps to my customer.
He brought in the reformed and re-engineered CR Audio 5050 amp I did up
about 5 months ago
which now has my far better circuit within, and over two hours with
several CDs
and swaps too and fro from PP KT88
to SE 845, we compared the performances. The SE had slightly more bass,
but
better space around instruments, air, and detail, and you felt more
drawn in to
where the musicians were. Both PP and SE were fine drinkable wines
indeed,
and the guy is looking forward to me completing the second mono.
He spent $5,500 for the CR Audio "Woodham" amp which was an absolute
pile of ****e
before I completely re-built it.
Not all PP amps are better than SE amps just because they happen to be
PP, and not SE.
The Woodham CR Audio amplifier is a tragic case of the designers being
right out of their depth.
The list of design no-nos were long as my arm.
I think CR which is supposedly a UK based company has their product made
to order in China
somewhere judging by the very poor skills used. They do look pretty, and
looks fool ppl.
What's the use of a good looking wife if she can't/won't cook?
My 845 were not much more expensive.
Well, once. I mucked
about with some SE transistor designs (2N301) briefly. I dumped them pretty
quick and went back to valves. Then I discovered KT88s (they cost AUS$25.00
each way back then). Mmmmm. Nice valves. FWIW: One of my instructors at
college was part of the design team at GE-MOV for the KT88.
The KT88 at $25 each were EXPENSIVE; 1960 was it? that makes the KT88 as
expensive than as
one KR Audio 845 is today maybe, ie, about $400.
Nowdays chinese KT88 or 845 are dirt cheap in real terms, and so what if
one has to use
twice the tube count in SE amps to get the same PO as a PP amp.
If you DO use enough tubes which ain't expensive ( Sovtek basic KT88 can
be had for
$35 each including freight if you buy 10 pcs from the US ) then SE isn't
any worse than PP,
and although 4 tubes in SE can only have about the same PO as an AB PP
amp with two,
The power is nicer power in the super critical region of less than 5
watts,
but you have to know what your'e doing.
But even 6V6 made in Oz in 1960 were expensive, and everyone was crying
poor back in those days,
and there wasn't much anything else you could use. Most ppl though
serious hi-fi was a pretentious
and frivolous waste of money. Hardly anyone could afford the luxury of
it.
807 were a favourite, bought from army disposal stores which continued
to sell
ex armed forces junk left over from excess production during WW2 until
after 1965. But they priced the NOS 807 about the same as any comparable
other new made tube like
6L6. In other words, they'd paid peanuts for the NOS 807 at army
auctions, and charged what the market would bear.
Some makers did fit single 807s in radios. I have repaired a couple, and
they sound equal to
a pair of 6V6 in PP, simply because with 8 watts from a lone 807, and
needing only
1/2 a watt to fill a room with sound with the type of sensitive speaker
used, the sound was blameless....
Everyone mostly made do with single 6V6s in countless radio and radio
grams, and only the rich
could afford the "deluxe" sets with PP amps. Of course these PP amps
were better generally.
The SE 6V6 amps in the radios and cheap grams rarely had much NFB.
Adding GNFB meant an extra tube for gain
so NFB could be applied to reduce this gain and get low Rout and
THD/IMD.
Makers hated spending on the extra tube. Beene Kounter & Associates had
their guys working
in most electronics manufacturing plants to ensure quality remained low.
Deluxe sets had twice the tube count, and instead of 4 watts you had 12
watts max,
and of course speakers all were about 95dB SPL 1M @ 1M.
Now speakers are maybe 88dB, and you NEED 3 times the power at least.
But 1960 speakers were very non-flat mostly, attrocious is the word.
Cones were thinly papered and being true flat cones not curvilinear,
they
tended to flap irregularly in the breeze. Some were quite good, the
Delauxe Rolas
fitted to Deluxe Radiolas sure were, and I have one in my kitchen radio
with EL34 SE triode amp with GNFB and its
a beautiful sounding AM radio, far better than any commercial set I have
EVER worked on,
simply because I designed it with a few more tubes and with linear
techniques used
in the IF amp and detector and audio stages.
But in 1960, we all grooved and bopped to the rock and roll anyway.
Johnny O'Keefe screamed his lungs out and overloaded all the gear used
to record him
and most of the source material we listened to was well and truly
pre-distorted before
our amps added another 0.5%, considered SFA in 1960.
KT88 PP could sure do 30 watts in pure class A and and much more in AB.
But for 35watts PURE class A, you only need 4 x 6L6, or KT66, or
EL34/6CA7, see
http://www.turneraudio.com.au/se35cfbmonobloc.html
3 KT88 may be used in the same amps, or 4 which is overkill.
Fine sound quality good measurements are the result of the ideas
employed to make these amps.
There isn't much extra work to make them in comparison to any other PP
monoblock amp
with 4 octal socket output tubes.
During today, I road tested a Luxman Receiver I'd repaired with a Dual
505 TT and the Lux
has an LED PO power readout for each channel.
The 3 watt level was only ever reached on bass rich music by Taj Mahal,
a 'Giant Step', from an LP
I got in about 1977. Thunderous bass in the music.
And tonight while I compared the PP amps with KT88 to SET with 2 x 845,
I doubt
I used any more power than 3 watts. The PP amp never moved out of class
A.
The SET had an easy time of it making 3 watts max. Its 50 watt ability
couldn't be reached because my speakers this time are average about 9
ohms,
and the amp only makes 50 watts if the load is 4 ohms.
The two 6 ohm SEAS Da'polito mids are series connected, 12" bass is 8
ohms, and tweeter is 6 ohms.
Never did we ever get close to clipping, or any audible distortion.
Yesterday I auditioned an ME850 which ran perfectly after repairs, and
it didn't sound any better than the SE or PP tube amp.
The SE seems to have more "foundational bass" and sweeter midrange.
Patrick Turner.
,
Trevor Wilson