Push-Pull EL34, triode connected, 15W Class A
Original schematic as far as I gathered fro a quick look. The supply section is missing and the ECC83 supply is not correct I think, the numbers don't add up. I'll take a closer look when I pull out the PCBs.
- Remove feedback
- Change 3K3 and 100R gridstoppers on the EL34 to 150R tants
- Change EL34 bypass cap to 100µF as that already goes below 5Hz with the 470R resistor.
- Change all the grid leak resistors to 100K tants
- Maybe change the EL34 to a 6L6 variant.
- Add the option to switch between triode and UL as per the original amplifier. Triode will give 15W, UL will give 25W. This should give some extra headroom when used for the bass section instead of full-range.
- Change tube to 6J9P or 6J11P in triode mode
- Change coupling caps to 100nF
- Grid leak to 100K
- Add 150R grid stopper
- Recalculate the bias and load resistors to match the 6J9P
- Change tube to 6C4S or 5842
- Recalculate load and bias resistors
- Change coupling cap to 100nF
- Remove two 47R resistors, reference grid to ground
- Bypass cap will likely need to be increased to a 470µF/16V type
- See if 6.3V will allow a simple DC version (voltage drops etc)
- Change 1N4007 to SiC diodes
- Add snubbers for tranny and diodes
- Replace all electrolyics in the B+ (now 20+ years old) to 450V Nichicon KX types
- Use MKP caps in last RC network for driver/gain tube B+ if there is room