I say go for it.. I'd say 15W-20W would probably be more viable, but 5W's would also get interest..

Side note, could you make me a 60W (conservatively rated) OT, 20hz-20khz full response, 6600: 4/8/16, about 3.5kg?

I would be interested in PP for the 1-5W range. All this SET is nice for hifi but not for guitar amps imho. There are almost no 'branded' alternatives, so price is not even too much of an issue.
More interested even if there would be some technical wizardry to make it possible to switch to many more watts (15-30) on the fly to get lots of clean headroom from the same amp.

@Makepeace: why would you rate the OPT conservatively? Underrating the OPT is a tried and tested guitar amp thing, since the lowest you are going to push out is maybe 80Hz so why worry about 20Hz based power ratings?

@makepeace: Can organise anything from 3watt reverb transformer to 100watt.
Gearhead is right, that is way low, and guitar amp output transformers do not have to
be HI-FI quality, but will still look for you. I like all my amps to have 4 8 and 16outputs

@gearhead: I do have a 15K primary pp transformer, that is 5watt rated.
I've thought of a design which an amp can switches from the output anodes to the
Phase inverter anodes?

@Gearhead and bottledtone

The full response thing relates to the fact that I'm going to be fiddling around with loooots of different push-pull pair output stages, from 6V6' to KT88's, and switching of secondaries for each one, as I'll mostly be working with just an 8ohm load. It was suggested to me by a person that really knows his stuff that I would get better response across the board with a high powered quality transformer with no distinct character, if you will, which are generally the hi-fi transformers. 20hz to 20khz response is a good indicator. If it can do that and can handle 60W comfortably, I'll be chuffed. UL taps would be a bonus.

Bandwidth is overrated :-\
OPT without character is like an inflatable lover ?

bottledtone wrote: I've thought of a design which an amp can switches from the output anodes to the
Phase inverter anodes?

Or preamp- phase inverter - cathode follower - output tubes and then switch to the cathode followers for better load handling? Sounds like a good idea. Maybe use ECF82?

Firstly OP, sorry for slight hijack :-[

Gearhead wrote: Bandwidth is overrated :-\
OPT without character is like an inflatable lover ?

HAha nice analogy.

Surely then bandwidth isn't the problem, rather the character? And surely two aren't necessarily independent? I mean someone said <don't know where they got that idea from..> that the Bassman was intended as a bass amp.. ?

If it wasn't, we'll never know and maybe Leo Fender didn't either.

If it was, surely they would have designed it around a transformer with good low end response, but guitars sound awesome through them, so it must also have had enough high end response? So large bandwidth, and still some - understatement - I mean *tons* of character?

Even still, something tells me that you should be able to build an excellent sounding amp with a "character-less" OT. :-\

Builders that I've encountered on other fora (18watt for one) use Edcor's OTs and they seem very happy with their outcomes.

Bearing in mind that my vision for this build is not your ordinary amp, I'm sure I'll be happy, even if it is to learn a cruel truth.

I'd be looking at 15W SE with a 2.5K primary and 4/8ohm secondaries. Similar to the Hammond 125ESE