Transfomer ID Help

[EWBrown]

Hi Eric & everyone,

I couldn't have said it better.... I drew up a schematic for just this purpose recently (using your fine 1773 OPTs), but probably won't be able to actually putting it together for a few more months. I was planning on the 10 ohm, 1 watt resistor method. That and keeping B+ around 340-350VDC to compensate for the fact the cathodes are 12 to 15VDC closer to ground potential than with "cathode" biasing which is more common with EL84 usage.

The current plan is to go "dual mono" with separate PA774s, with C354 chokes for each channel, and perhaps feeding the input/driver with its own power trannie and DC filaments. So I guess that'd be dual-and-a-half mono... If I have the echassis room, maybe tune rectification - two more trannies, 5VAC @ 3A.

I've always liked the VTL "tiny 25s" and this would be my own take on them, with a couple of minor twists and turns.

/ed B in NH

[Ty_Bower]

After the dust settles, I'll talk about DC and AC, or dynamic, balance, which Ed Brown touched upon earlier...if anyone's interested.

I'm interested...

[paart]

Hi!
Looks like S. Parks made a good case for setting the output balance with a distortion analyzer, rather than just a static setting, to overcome deficiencies in output xfrmrs. Someday I hope to own an analyzer!

I've been intrigued with the idea of converting an ST-35 to fixed bias for many years, but most of the design books that I've read seem to discourage the idea for amps and output tubes in the power range we are looking at, here. If anyone has opinions and results to share on this change, I'll be very interested.

[Ty_Bower]

No results, not yet at least. I've listened to a fixed bias EL34 sized amp and compared it to my DIY ST35. I'm certain the bottom end has more punch on the bigger amp. Funny thing is, I do my listening late at night when the kids are sleeping upstairs. So, I'm never running at plaster cracking volumes. I would have expected the two amps to perform nearly the same at low levels, but I'm not convinced that is the case. I'm left wondering if fixed bias is the reason why...

[erichayes]

Ty, an' all,

Give me a day (or give me a call) to collect my thoughts regarding this rather moldy thread.

Amazing how things come back to taunt you . . .