I am fixing up an old Heathkit SA-2 for a friend, and I have got the thing working quite well. The problem I can't seem to sort out is that the phono (mag phono) input does not have sufficient gain. When playing any other source material, you get lots of volume. With Vinyl and a moving magnet cartridge the volume is very low. So. I replaced almost all the components in the phono-stage with new ones. 20% coupling caps got replaced with 5%ers and all the 10% resistors got chucked in favor of new 5% resistors. I replaced every part in the signal path up to the second screen, and still no luck. (Many of the resistors had drifted 20%) I also cleaned the selector switch. I think my next plan is to measure the AC voltage out of my phonostage, (at the selector) then measure the Ac voltage from the Tape deck, and make sure that I am seeing the same AC voltage from the output (plate) of the phonostage as I am getting from the tape deck (without amplification).
here is a schematic.The Free Information Society - Heathkit SA2 Electronic Circuit Schematic
If i find that the Ac voltage from my first triode is insuficient, what is the best way to bring it up? I have already tried 3 sets of known good tubes so I know it is not bad tubes. Any guesses?
here is a schematic.The Free Information Society - Heathkit SA2 Electronic Circuit Schematic
If i find that the Ac voltage from my first triode is insuficient, what is the best way to bring it up? I have already tried 3 sets of known good tubes so I know it is not bad tubes. Any guesses?