Hmmm... What to make?

[I'm a beginner!]

Hi all!!
Just hoping for some inspiration really...
I have been given a power transformer as a gift which is very nice, as like everybody I seem to be on a tight budget!
It has three secondaries, none are centre tapped so bridge rectifiers will be the path for me... one at 385vac 0.4A, one at 40vac 0.2A, and one at 6.3vac 5A. At least that's what the label says!!
For a while I have wanted to do a build with a couple of EL34s, but I'm not sure if this will be a good idea or not... I was not given an OT with the transformer, but I was given a stack of EI96 laminations and several spools of magnet wire. I can wind an OT, but on EI96 I don't think it would be happy going far above 50W, and with this power transformer 2 EL34 would go way above this unless I bias really low... So I just thought I'd ask what ideas for builds people would come up with if they had been given the same freebies as have landed in my lap!

[Steve Conner]

Bias is a poor way of controlling power. To a first approximation, it doesn't affect the maximum output power at all. A better way to limit power is by reducing the screen voltage. This also makes EL34s more reliable.

Cathode bias can also help to get rid of some excess voltage and limit the power further.

Good luck winding your own OT! If you don't have a ready-made plastic bobbin, you could go with a taller stack than normal to increase the power handling.

[R.G.]

It has three secondaries, none are centre tapped so bridge rectifiers will be the path for me... one at 385vac 0.4A, one at 40vac 0.2A, and one at 6.3vac 5A. At least that's what the label says!!

If you rectify those, you'll get
385 * 1.414 = 544Vdc before ripple and sag, perhaps 510-520 under load; the current ability will be about 235ma
40*1.414 = 56.56, about 55V after the diode losses, good for a bias supply, I guess

You can add up the heater currents from whatever tubes you use, just remembering to stay under 5A. EL34s draw 1.5A each, so a pair will eat 3 of your 5 amps. 6L6's draw 0.9A each, so a pair would be 1.8 out of the 5A. 12AX7s are 300ma each on 6Vac, so you have room for six of them with one pair of EL34s.

I was not given an OT with the transformer, but I was given a stack of EI96 laminations and several spools of magnet wire. I can wind an OT,

Winding an OT is a big undertaking. Winding a good one probably ought to be approached as several complete iterations. I don't know your level of transformer winding skills. Transformer winding, especially OTs, is a highly specialized skill.

but on EI96 I don't think it would be happy going far above 50W, and with this power transformer 2 EL34 would go way above this unless I bias really low... So I just thought I'd ask what ideas for builds people would come up with if they had been given the same freebies as have landed in my lap!

A power amp is properly thought of as a power supply which has a small lump (consisting of the entire power amplifier circuit) appended to it to let some of the power out in a controlled way. The power transformer output is about 119W of DC. You can get maybe 50-60W rms of audio out of that, but you probably can't get 80-100W out with it biased into linear conduction.

I've wound transformers before. I would look at the voltage and currents available from the PT, pick a pair of output tubes, and buy an output transformer to match. I would put the laminations and magnet wire in the shop to think about and tinker with.

[I'm a beginner!]

Hey thanks for the replies!
cathode bias! D'oh! I didn't even think about it, I just saw the third secondary and my brain started going "ooh, a bias supply..." I like the idea of lower screen voltage too, maybe 300 - 350V will be ok... not sure, will have to sit down later with pen, paper and calculator...
Yes, 6L6 were considered, they do have that advantage of drawing less on the heater current, but EL34s are tempting because I have never used them, wheras the last build was 6L6 so it would be nice to work with something different.

Winding the OT doesn't worry me too much, I have wound transformers before and there isn't alot to them... bobbin, wire, insulation, laminations... and technique which is patience and care. Designing them is a much more daunting proposition, but there is enough information about existing OTs for me to be able to pick one that is known to work with approx 50 or 60W EL34 amp into the pretty standard 8R and 16R and copy the winding pattern. It's not like I'm trying to custom design an OT to match a 200W monster to a switchable output of 1.5R or 37R. That would make me run away!!!

I must say once more, thanks for the replies!! I read here often and it is amazing how much I learn from the contributors here!
Thank you!!