Appologies if this has been asked many times before - I looked for
FAQs and didn't find any on this group.

I'm looking for a stereo tube/valve amp design, about 20 watt per
channel - sufficient for an average living room in detatched house.

Audio sources will be CD, FM/DAB tuner, Garrard GT25AT1 turntable,
iPod too maybe so nothing really fancy. I haven't got "golden ears" so
probably won' t really appreciate the difference between a 5,000 UKP
($10,000) and a 500 UKP ($1,000) amp.

Speakers probably a pair of LS3/5a or AR18, but may change these if
necessary.

I'd prefer a kit including the drilled chassis, but a design that I
can build from scratch, providing the parts are all easily available,
will also be considered.

What UK/US kit or circuit design would you suggest? It would be nice
if the valves were exposed through the top of the cassis, but this
seems to be the case anyway in the valve amps I've seen. I have looked
at what World Audio Design have on offer, and they seem to have a good
name, but are there others equally good or better?

I prefer not to pay for a kit includes "special audio quality
components" that cost 10 times the statndard parts, as again, if they
really do make a difference, I doubt I could hear it.

I'm a broadcast engineer, but not had much exposure to valve audio
gear. I doubt I could tell the difference between a good valve amp and
a good solid-state amp (OK maybe I could, but to me they would
probably just sound "different").

I would simply like to have a good-ish valve amp with character, a
warm glow, you know the type of thing...

Thanks.

Ian

Look through the various old DIY audio books and see if anything
strikes your fancy. Scratchbuilding will be far more educational of
course. Modern books worth reading include but are not limited to
Morgan Jones' Valve Amplifiers and Building Valve Amplifiers, Bruce
Rozenblit's Beginners Guide et al, and-not intended for DIYers but
useful- the VTL Book.

http://www.audioxpress.com is one US based source.


In the UK you might contact Sowter Transformers who wind classic
GEC/Mullard , Leak, and Radford OPTs, and the kind of amps you can
build ultimately comes down to what transformers you can get.

You could of course build the old Williamson design, which with a pair
of about any beam power tubes strapped triode, gives roughly fifteen
watts, or twenty if used with an Ultra-Linear connection.

I would avoid anything using EL84s, and unless you are very wealthy,
true triodes. Single ended is a deluded crock and you would be advised
not to waste your time IMO.

On 28 Jul 2005 16:19:22 -0700, "Bret Ludwig"
wrote:

I would avoid anything using EL84s, and unless you are very wealthy,
true triodes. Single ended is a deluded crock and you would be advised
not to waste your time IMO.

And I'd suggest the exact opposite. Just proves that it takes
all kinds to fill the freeways.

Good fortune,

Chris Hornbeck

Triode amps can work well but they tend to be quite expensive or a lot
of trouble to get to work. EL84's are terribly nonlinear and are poor
choices for hi-fi (they work well in guitar amplifiers where people
WANT distortion.) And as far as single ended goes, no conventional
single ended amp will provide true fidelity in full-range application.

On 28 Jul 2005 20:23:07 -0700, "Bret Ludwig"
wrote:

Triode amps can work well but they tend to be quite expensive or a lot
of trouble to get to work. EL84's are terribly nonlinear and are poor
choices for hi-fi (they work well in guitar amplifiers where people
WANT distortion.) And as far as single ended goes, no conventional
single ended amp will provide true fidelity in full-range application.

Large and compelling elements of truth. So to turn the tables a
little bit, why post on r.a.t.? IOW, what positives about valves
as audio amplifiers interest you?

And, if you feel so inclined, please include your reservations.

Thanks,

Chris Hornbeck

Positives, fun to work with, better dynamics because of higher
voltages, easier to troubleshoot, has OPT for speaker
isolation/protection, has nostalgia appeal. Downside: finite tube life,
maintenance, lower current capability, tolerance for poor design and
operating practice covers up poor design practices sometimes. Either
can sound good or bad, tubes sound bad in a way people often mistake
for good, which leads to confusion.

A really well designed tube amp can sound and measure well and provide
long life with little fuss. Solid state usually fails outright and gets
your attention immediately when it does. However well designed ones
rarely fail.

I suppose it comes down to preference. But people with no technical
abilities and a simple desire to listen to the music with no fuss are
probably better served by a solidd state unit.

Bret Ludwig wrote:

Triode amps can work well but they tend to be quite expensive or a lot
of trouble to get to work.

Triode amps are easy to get to work, but are more expensive
because the plate efficiency is lowest.
But they give better linearity than other types of tubes
at the same power; eg, trioded EL34 in triode will have less thd than
pure pentode at 10 watts.

EL84's are terribly nonlinear and are poor
choices for hi-fi (they work well in guitar amplifiers where people
WANT distortion.)

EL84 are not any more non-linear than many other tubes, and they
can be VERY linear if set up right.

And as far as single ended goes, no conventional
single ended amp will provide true fidelity in full-range application.

It depends what you mean by conventional.
If you mean some old SE PA amp, sure, it may have poor response.

But unconventional SE amps be they triode or multigrid types
can provide true hi-fi that many find sounds second to none.

Its not hard to make an SE amp that has low Ro, thd below 1% at full po and
declining
with Vo, wide bandwidth from 10Hz to 65 kHz, -3dB,
and low noise.

Patrick Turner.

"Bret Ludwig" wrote in message
oups.com...
Positives, fun to work with, better dynamics because of higher
voltages, easier to troubleshoot, has OPT for speaker
isolation/protection, has nostalgia appeal. Downside: finite tube life,
maintenance, lower current capability, tolerance for poor design and
operating practice covers up poor design practices sometimes. Either
can sound good or bad, tubes sound bad in a way people often mistake
for good, which leads to confusion.

A really well designed tube amp can sound and measure well and provide
long life with little fuss. Solid state usually fails outright and gets
your attention immediately when it does. However well designed ones
rarely fail.

I suppose it comes down to preference. But people with no technical
abilities and a simple desire to listen to the music with no fuss are
probably better served by a solidd state unit.

I think the gentleman wants the "tube experience." Nice warm glow and such.
It's like some ppl like turntables because of the touch, ritual, active
involvement.
He also wants a kit so he can be proud to say perhaps to his friends, or?
"see, I built that myself".
Tube stuff , if we can empathize and take ourselves out of the equation, has
appeal that include more than the sound to many. Good luck to him. Maybe
next year he might be asking about global feedback & such.
Cordially,
west

Since you live in UK, in the 20w range, of course i suggest the Quad II
design.
A good amp. that is easy to find for you in the UK.

Ls3/5a / quad II is a good marriage.

You may find a pair in bad condition (tons of dust,...) with the power
and output tranformers ok. You test them for shortcuts.

And you could rebuild them completely (kt66 are easily available) with
new resistors and new capacitors where needed.

That has proven educational for me.
Also it will cost you less than build a similar quality amp from
scratch.

Of course it may take some time to find ones at a reasonable price. But
i think there are many of them in the UK.

Sowter also is a good advice, but i'm not sure they will be in your
price range. It is said that they make one of the best otps.

Patrick Turner wrote:


It depends what you mean by conventional.
If you mean some old SE PA amp, sure, it may have poor response.

But unconventional SE amps be they triode or multigrid types
can provide true hi-fi that many find sounds second to none.

Its not hard to make an SE amp that has low Ro, thd below 1% at full po and
declining
with Vo, wide bandwidth from 10Hz to 65 kHz, -3dB,
and low noise.


If it will do so I couldn't fault it. But can you point to a
documented design that does this? I would like to see how several known
issues are dealt with.

Hello Ian - can you contact me on - I may have
what you want. Andy

"Bret Ludwig" wrote in message
oups.com...
Triode amps can work well but they tend to be quite expensive or a
lot
of trouble to get to work. EL84's are terribly nonlinear and are
poor
choices for hi-fi (they work well in guitar amplifiers where people
WANT distortion.)

If EL84's are so bad, how come the "Mullard 5-10" design, at least the
UL version, delivers 11 watts at less than 0.1% distortion? I built
two in the early 1960's.

And as far as single ended goes, no conventional
single ended amp will provide true fidelity in full-range
application.

I agree with that, but then my philosophy on audio power amplifiers is
a "straight, thick wire with gain", easily done with solid state these
days. The reason I play with tubes is the "historical warm fuzzies"
brought on by the glowing heaters g (also it's what I learned on!)
Cheers,
Roger

Ian,
start here----http://www.worldtubeaudio.com/
You'll find what you are looking for
enjoy
Mike M

Hello Ian - can you contact me on aeatartsandmedia (at) aol (dot) com -
I may have
what you want. Hope that works - emails seems to be truncated here.
Andy

Very many thanks to all those who posted their suggestions. The Quad
II idea looks particularly promising. I restore (and rebuild when
necessary) vintage radio gear, so doing the same to a valve amp is an
obvious idea that never occured to me!

Looks like I may need a preamp to go with a Quad as I've done a bit of
research now and it looks as if they need more audio than a phono
level will provide...

Cheers,

Ian

My question is, what is an unmolested Quad II monoblock worth in the
UK?

A pair of Quads on ebay goes from =A3300 to =A3600 depending on condition.
Leak Stereo 20s are usually around =A3300 and can be modded very nicely
indeed, plus the output transformer can be rewired to make it sound
better. We're still talking pentode amps with feedback here, and with
the price of Russian and Chinese 2a3 and 845 valves barely over =A320
each, it would be more enterprising to build a push pull amp using
those - the 845 can also be used as a low voltage amp for 400-600v HT
meaning it doesn't need suicidal voltages. There are several all triode
output stages once you get into multiples of the smaller triodes like
12b4, 6S4A, 6CK4, 6AH4, 1626, and also doubles like the 6BX7 and the
beefy 6528. Combine that with a modern input stage using a constant
current sink and you have something very nice.

Andy Evans wrote:

A pair of Quads on ebay goes from £300 to £600 depending on condition.
Leak Stereo 20s are usually around £300 and can be modded very nicely
indeed, plus the output transformer can be rewired to make it sound
better.

Gee, rewinding the opts on these amps is a large chore though.
Not all that much is available that is much better.
The size of the Quad OPT limits what needs to be done to
improve its performance. Almost anything else made is an improvement on the
Leak OPTs;
these are pretty lossy, with high leakage inductance.

Quad II in 8 ohm config has 17% winding losses in its OPT.

Its not good, but then these old amps can be still be made to perform
better, and perhaps sound better.
The PS with nearly all old british tube amps is appalling, and the best
thing
is to retire the existing stupid low value caps and tube rectifier,
and put in SS rectifiers and much larger modern electros.
Since B+ will be higher with SS diodes, you can use CRC with 100 uF to
start with
and then about 100 ohms plus use the
existing rectifiers in series with the 100 ohms as a slow turn on series
diode.
GZ34 has R = 40 ohms with 150mA. The second C should be a 470 uF /450v,
and the series R is to reduce the B+ to what it was with the tube
rectifier.
But ripple voltage at the CT in a Quad II is reduced from 17vrms to around
100mV.
This reduces virtually all the imd produced by PS rail noise.


We're still talking pentode amps with feedback here, and with
the price of Russian and Chinese 2a3 and 845 valves barely over £20
each, it would be more enterprising to build a push pull amp using
those - the 845 can also be used as a low voltage amp for 400-600v HT
meaning it doesn't need suicidal voltages. There are several all triode
output stages once you get into multiples of the smaller triodes like
12b4, 6S4A, 6CK4, 6AH4, 1626, and also doubles like the 6BX7 and the
beefy 6528. Combine that with a modern input stage using a constant
current sink and you have something very nice.

Building a tube amp from scratch without at least building a preamp
is diving into a treacherous situation.

With kits, you don't have to know anything, but beginners still make all
sorts
of mistakes and have a saga of problems.

With designing one's own amp and building it, you **MUST** know a heck of a
lot about
electronics, and its a very slow process if you don't have any natural
ability
with metalwork and using tools properly in a workshop.


Patrick Turner.

Gee, rewinding the opts on these amps is a large chore though.
Almost anything else made is an improvement on the Leak OPTs; these
are pretty lossy, with high leakage inductance.

what you do is take off the transformer covers and re-wire it so all
the three secondary windings are used. this only gives a 4 ohm option,
but it sounds better. No rewinding necessary. It's a quick and
effective fix. I have a diagram if needed. Andy

The best first tube project is not an amplifier of any kind but rather
a regenerative radio receiver. These can be built from books intended
for boys from 1935 to 1965 and will be very informative. A small guitar
amp in the class of a Fender Champ is another good starter project.


With the old literature there are usually detailed layouts and even
chassis construction diomensions so building from these books and
articles is a Good Idea for the true beginner. You can lay the chassis
out on a sheet and have a local sheetmetal shop bend and shear as
needed for a few dollars.