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Old 25th June 2003, 04:22 PM   #1
Dave S is offline Dave S  United Kingdom
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Default Help Me Choose a Sensible Power Amp

I'm looking valve power amp to build - either from scratch or as a kit.

I have ruled out flea power at one extreme and lots of expensive tubes at the other extreme. Some sort of KT88/6550/EL34 PP amp seems to be the way to go, this will give me the right power level at a reasonable cost i.e. 20W to 50W for about £600.

Two kits which look quite promising are:
http://www.diyhifisupply.com/diy_kits/the_ella.html
and KaT34 or KaT6550 on:
http://www.worldaudiodesign.co.uk/amplifiers.html
http://www.worldaudiodesign.co.uk/pdf/kit34crt.pdf

I'm not after the ultimate in sound, however it's got to be in the very good category or it's not worth bothering. Any opinions, any other suggestions? UK availability is a bonus.

Thanks,

Dave
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Old 25th June 2003, 06:13 PM   #2
EC8010 is offline EC8010  United Kingdom
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I suspect that it comes down to whether you want to build using new ironmongery or old. If you don't mind old, then you can scout around and buy old amplifiers and refurbish/rebuild them. A couple of days ago, a pair of 600W KT88 amplifiers went on eBay for £520. They would have needed a huge amount of work, and 600W is more than you need, but you can see what I'm getting at.

If you buy new, you will have trouble assembling a kit of parts for the same price as, for instance, the WAD kits.

Regarding your "not worth bothering" point, does this mean that you are capable of doing really nice metalwork and electronics, but are simply looking for a bit of hands-on advice about valves?
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Old 25th June 2003, 08:29 PM   #3
Dave S is offline Dave S  United Kingdom
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Quote:
I suspect that it comes down to whether you want to build using new ironmongery or old. If you don't mind old, then you can scout around and buy old amplifiers and refurbish/rebuild them. A couple of days ago, a pair of 600W KT88 amplifiers went on eBay for £520. They would have needed a huge amount of work, and 600W is more than you need, but you can see what I'm getting at.
I have good electronics and ss knowledge but I'm new to valves, so I don't think I'm capable of identifying appropriate iron and getting a good final result. I have tried a friend's Grant-Lumley GA50 (using KT88s, restored as appropriate, no "audiophile" bits) in my system and thought it was pretty good - so maybe I should look for one of these or possibly a Beard - the problem of course is actually finding one.


Quote:
If you buy new, you will have trouble assembling a kit of parts for the same price as, for instance, the WAD kits.
Quote:
Regarding your "not worth bothering" point, does this mean that you are capable of doing really nice metalwork and electronics, but are simply looking for a bit of hands-on advice about valves?
The metalwork is always a pain for me so I should be realistic and avoid this. Building the circuits is fine - I've just completed a scratch built Grounded Grid with no problems and I've built loads of ss stuff.

Hands on advice on the following would be most appreciated:

WAD uses valve rectification - is this really a benefit or is it just a marketing feature?
The Ella is more hassle to import and uses a pcb which may be less ideal that hardwiring. It is also very sensitive (150mV) which is a nuisance for use with an active pre - is it worth even considering it compared to the WAD kits?
Is it worthwhile putting KT88s in the KaT34 or KaT6550?
Would you expect the WAD kits to sound better than the Grant GA50?


So overall.....
WAD seems to offer the lowest risk route, but before I go ahead I wanted to see if anyone had any better ideas or alternatives.

Many thanks,

Dave
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Old 25th June 2003, 09:42 PM   #4
EC8010 is offline EC8010  United Kingdom
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Default It's all in the detail...

Sounds to me as though you would be best going for a WAD kit, and perhaps modifying the driver circuitry. All the metalwork is done for you, but they are hardwired, and if you're clued up on SS, modifying is no problem at all.

I'm unconvinced about valve rectifiers being better. Yes, they switch on and off more cleanly, and they protect against switch-on surges, but they need extra heater supplies and have higher "on" resistance. Having said that, I appear to have slightly more amplifiers around the house with valve rectifiers than SS.

I can't comment on the sound of the WAD kits or the Grant Lumleys, because I haven't heard them. The only comment I would make is that (from memory) the GL had bigger output transformers. When it comes to output transformers, biggest is almost always best.

The thing with valves is that you can't generally apply very much feedback. That means the design has to be good in the first place. Every aspect of every component (and it's place in the scheme of things) has to be considered. Do that, and you will end up with a cracker of an amplifier.
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Old 26th June 2003, 03:46 PM   #5
Dave S is offline Dave S  United Kingdom
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Default Thanks for the help

These seem to be my options in the £500 to £1000 range:

a) Buy a 2nd hand Beard P100
b) Build a WAD KaT34/6550
c) Buy an Affordable Valve Company EL34 or KT88 amp
d) Build the Edison Model 60 power amp
e) Build the DIYHiFi Supply Ella

Actualy I just found a thread by Erik Andersson about some of these amps, but the only info I can glean is that they are generally fairly good but the iron will be a bit comprimised by being built down to a price (obviously not in the Beard).

Goodness only knows which way to go
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Old 26th June 2003, 04:22 PM   #6
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Hi Dave,

I bought a WAD kit (2A3PSE) for my son to make as his first valve amplifier. Whilst not the simplest kit in that it is tag strip and hard wired throughout, the instructions where good and the kit was straight forward to make. The sound is pretty good - but can be improved on - so it's a good base on which to experiment.

About 50% of the kits have a PCB instead of hard wiring. They are good value too. WAD have an active and informative BBS accessed through their website.

ciao

James
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Old 26th June 2003, 04:23 PM   #7
EC8010 is offline EC8010  United Kingdom
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Default Scratch build?

What makes you think that Beard was immune to commercial pressures?

Hmmm. Reading between the lines of your post, I would say that the only compromises you are prepared to accept are the ones you make yourself. I also note that your budget has quietly increased.

You may be interested to know that Woodside Electronics still make Radford output transformers (which were the amplifier's strong point). When I phoned them ten years ago, they said it was the same little old lady who made them for Radford. It's probably a different LOL now.
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Old 26th June 2003, 05:54 PM   #8
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Hi,

Quote:
What makes you think that Beard was immune to commercial pressures?
I certainly wouldn't but from the entire range of product Bill put out the P100 was O.K., provided you put devent valves in it.

The GL P50 had a good rep sonically but no way of finding a digram for any of those on the web as far as I know.

Still, being in the U.K. a secondhand EAR or Michaelson and Austin comes to my mind although I think those use a PCB...

As for the WADs I never heard anyone complain about them and as EC8010 mentioned, being hardwired makes it easier to mod them.
My choice would be the 6550 one if I needed the power or the 2A3 one if I didn't.

The EL34 never really impressed me, the US 6CA7 is another story....much better and not so equivalent to the EL34 as most people seem to assume.

In these digital trash days a valve rectifier may be an advantage in many situations, plus the natural softstart mechanism is much more gentle on the PSU caps and valves.

OTOH, diode noise can be tackled and in some situations may be preferable.

Cheers,
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Old 26th June 2003, 06:13 PM   #9
Dave S is offline Dave S  United Kingdom
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The Beard stuff looks to have some pretty hefty iron judging from its size and weight and the fact that it can do 90W+ at 20Hz.

The Grant GL100 circuit is available here:

http://www.drtube.com/audioamp.htm#Grant

The owner of the GL50 thinks the circuit is very similar.

The concers I have over the WAD are:
They sometimes seem to have mechanical hum problems (with various fixes).
They run the tubes hard (so I'm told).
They charge £80 for a cage.
How good are the transformers?

Doesn't the budget always creep up?

Papworth TVA10 l(or TVA50) looks promising but we are probably talking £1K+

BTW if Frank thinks the Beard is OK that may well mean it's s**t hot for me!
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Old 26th June 2003, 06:42 PM   #10
EC8010 is offline EC8010  United Kingdom
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I don't know about the Papworth TVA10, but the original Michaelson & Austin version was a nightmare, and you wouldn't want to touch it with a sterilized barge pole.
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