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#1
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Tube/valve amp kit question
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 |
#2
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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. |
#3
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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 |
#4
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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. |
#5
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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 |
#6
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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. |
#7
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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. |
#8
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"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 |
#9
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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. |
#10
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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. |
#11
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Hello Ian - can you contact me on - I may have
what you want. Andy |
#12
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"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 |
#13
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Ian,
start here----http://www.worldtubeaudio.com/ You'll find what you are looking for enjoy Mike M |
#14
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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 |
#15
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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 |
#16
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My question is, what is an unmolested Quad II monoblock worth in the
UK? |
#17
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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. |
#18
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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. |
#19
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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 |
#20
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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. |
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