valve amp?

[The Dong]

On 19/10/2011 22:39, Tom Adam wrote:

> So does anybody have any pointers to this kind of stuff?
>
> I got him at least convinced to first try out the amp (and probably
> speakers) before buying ;-)


This is only what I know from lots of reading and futzing. The only 
valve amp I use for music is a Kit PP ecl82 from World Audio Designs, 
which does sound rather good, but is no longer available.

A lot of this is about your budget and whether your friend, or one of 
their friends, can build up a kit amp, because a lot of valve amps these 
days can be bought as kits too. Some will be tag board/turret, some with 
PCB's, but all with tubes, of course. The 'Iron', or transformers are a 
big part of how good the sound will be, power trans, maybe a choke and 
interstage and the output transformers. These can get very expensive, so 
some compromise will be necessary, because the 'top o' the range' output 
transformers run into £1000's, but aren't really required buying ;)

The main 'types' are SE (Single ended) or PP/Ultralinear (Push pull, 
ultralinear is a type of push pull) The single ended are mostly low 
power output, say a few watts up to 10+ watts, due to having only one 
power output tube. The push pulls are generally louder, with ecl82/86 
having about 10W, el84 slightly more, and more power with more esoteric 
tubes.

A low budget amp might be based on a PP EL84, which should make a great 
music amplifier.

Example:

http://www.world-designs.co.uk/el84.htm

I know the above example is expensive, I actually have the schematic of 
that one, so if you can buy all the equivalent parts and build it from 
scratch, divide the price down..

If you have a bigger budget, an SE 300B has been all the rage for a long 
time, but with a good pair of 300B's costing well over £100, I have not 
been able to afford that route ;)

Speakers are definitely important, especially with the lower power amps.
Efficiency should be above or around 90dB a watt or so for good 
listening levels. Single drivers (no tweeter, or maybe a super tweeter) 
of the Lowther or Fostex range are recommended, but cheaper equivalents 
can be tried (e.g. Radio Spares used to sell a version of the Fostex 
range for lots less money) Single, full range drivers don't have that 
nagging, metallic tweeter sound, that's the best I can describe it.

Building one from scratch, or a Kit is the best I'd say. Speakers too.
A kit tube amp should only take a day or two for someone who can solder 
well and follow instructions. Few valve amps are very complicated, 
that's why I like them (easy trouble shoot and repair)

Good luck :)