I have gone through a few really nice EL34 amps, and then got an eye opener from the 6L6 family. While older G and GA types are a bit on the 'spensive side, NOS 807 and Svetlana 'Winged C' 6L6GC are nice valves in the cheap end of the pool. There are *MANY* good sounding valves in the cheap end BTW.

For low NFB designs, I got a really nice design from Heyboer. It's a copy of the Peerless S-265, a 20-20 Series, 10k:16,8,4,2/40 Watt design with a core bigger than the Dynaco 60W Mk.3 design. The winding design leaves it really easy to put U-L screen taps where the design calls for them( semi-custom designs do have their benefits, No? ). Or putting in more than a single pair of taps if you want to experiment a bit. No matter what sort of religious dogma might be heard about winding OPT's, it isn't all that dificult to get a good design.

Just pick a design which can be used in a few different circuits. For example the 265 can be done with 807's, 813's and GM-70/845 designs. If proper care is taken, silly B+ is not required, and 40W is a lot of power if you have efficient speakers.
regards,
Douglas

Joe

Tried them as phase splitters, in-circuit and on the bench. While the ones designed for phase spliting work well on the bench, they did not sound as good as a simple diff amp.

Such things do make good PP grid chokes. Leave teh CT split and you can do individual fixed bias.
regards,
Douglas

Joe

Joe

I got an improvement when I put g2 to the 30%. 9.5 Watts and a bigger more natural sound. I keep grinning to myself every time I hear something soooo inexpensive sound so good.

I ran the amp with a signal generator, and go no misbehaviour at the frequency extremes. 9.5 watts down to where my signal generator got a bit loopy( ~16 cps ), and it ran out into the ultra-sonic with out any wiggles in the curve. I will do a more comprehensive measurement when I am done with the new linestage.

As far as other ratings, like DC I would stick with the originally published specs. I think it was 120 mA per leg, and 10% imbalance. With fixed bias, I can get to a small fraction of that easily.
regards,
Douglas

Something like a properly done Dynaco Mk.4. Choke input filter. Oil cap for the PS energy storage and a 20 Hy/200 mA choke. I will probably step back to 15 Hy because I have a pair of them the size of Mk.3 outputs. Killer overdone PS. Hell, it will be taking no more than about 80 mA. 35 each for the power valves and 5 or so for the front end.

good ideas are just that: good. Keep 'em comming.
regards,
Douglas