I have a bunch of Soviet made 6H7Cs (sort of like 6N7 but with beefy ratings FOR THE GLORY OF THE PEOPLE) - I was thinking about making a relatively inexpensive headphone amplifier with 4 of them. I'm not sure what a schematic drawing program that is good for tubes is (recommendations?) but I'll describe it for now. Each channel: 1 6N7 connected as a differential amplifier, constant current source long tail consisting of a compensated Wilson current mirror with some kind of current source feeding the mirror, directly coupled to an output 6N7 cathode follower - both sections paralleled up to raise the transconductance and drop the plate resistance, and feed that with the cascaded LM317 current source I was reading about the other day. Take a little feedback from the output back to the inverting input of the differential amp, and that's about it.
I have a some 6X5 rectifiers that can supply up to 75ma which seems like it would be enough for this amplifier. With the constant current sources the PSRR should be pretty good, so I'm thinking I can get away with just having a standard CLCRC filter. The 6H7Cs draw about 0.8 amps each though, so I might use a separate filament supply for them and bias it up through the center tap so I can do the direct-coupling thing. Use the main power transformer filament winding to feed the rectifier and power the current sources in the differential amplifier with a solid state voltage doubler. Total tubes used: 4 6H7Cs and 1 6X5.
Any feedback would be appreciated! I've never done a circuit with feedback into a tube differential pair before, so any advice on that would be appreciated. What kind of currents might be good to have running through the input and output constant current sources?
I have a some 6X5 rectifiers that can supply up to 75ma which seems like it would be enough for this amplifier. With the constant current sources the PSRR should be pretty good, so I'm thinking I can get away with just having a standard CLCRC filter. The 6H7Cs draw about 0.8 amps each though, so I might use a separate filament supply for them and bias it up through the center tap so I can do the direct-coupling thing. Use the main power transformer filament winding to feed the rectifier and power the current sources in the differential amplifier with a solid state voltage doubler. Total tubes used: 4 6H7Cs and 1 6X5.
Any feedback would be appreciated! I've never done a circuit with feedback into a tube differential pair before, so any advice on that would be appreciated. What kind of currents might be good to have running through the input and output constant current sources?
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