zippy1540 wrote:A friend of mine just ran into a bunch of 807's and wants me to build an amp for him. He has a bunch of 6sn7's also. Anyone have any suggestions for a push pull schematic i can build him? I'm thinking i'll need a 12x7 or 6sl7 and use the 6sn7 as the phase splitter. For anyone who has built an amp using 807's what operating points seem to work best? output impedance?
Just gathering ideas at this point, the power supply will probably be a tube rectified CLCRC setup but i'm not too worried about that.
Thanks,
Paul
Lucky him. 807s can work great if you take the necessary precautions with the design. 807s like to make higher order harmonics, so some form of local NFB is a good idea. They also like to make snivets, so screen stoppers are mandatory. Once you have those problems taken care of, they perform with excellence.
Suggested schemo: Vixen (attached)
This design puts everything you mentioned to good use: 6SN7s, 6SL7s, and 807s. Also included: active screen regulation as having a stable, Lo-Z source for the screens improves linearity. This is a feature seldom seen with commercial designs, and very few professional designs. One exception was a theatre amp that used 807s as finals. The regulator can be hollow state, or solid state with high voltage MOSFETs.