sony6060
Super Member
Fisher amps use some of the 12AX7s in in the power tube cathode circuit to develop power tube cathode bias plus apply DC (direct current) to the filaments to eliminate AC (alternating current) hum. The 12AX7 tubes are set up to use 12 volts each in the Fisher amplifiers & receivers at the phono, input and tone sections. Do note the 12AX7 can be wired for 6.3 volt or 12.6 volt operation depending upon the wiring at the socket.
Some Sovtek 12AX7LPS do not have equal current draw in each filament. A wide variance will starve one side of the 12AX7 filament. These unbalanced tubes shows up on tube testers with unbalanced emissions that use 12.6 volts filament on 12AX7 tubes. The unbalanced 12AX7 filament draw can cause one channel to sound mildly or even extensively distorted.
Thus, if you purchase a load of these 12AX7LPS due to the low cost of re-tubing a Fisher, the phase splitters operate at 6.3 volts and in the case of the receivers, the phase splitters and multiplexer operates off of 6.3 volts. Use the unbalanced 12AX7LPS filaments in those positions. The unbalanced filaments will not matter due to the filaments are wired in parallel.
Perhaps the Russian Genelex Gold Lion 12AX7 long plate gold pin tube that sounds the same to me as the 12AX7LPS are factory selected for equal filament draw. However, the Genelex Gold Lion costs 2.5 times of the 12AX7LPS!!! (Ya, how about that 10 cent coffee, Starbucks is killing me!)
Long Live the King- FISHER
Some Sovtek 12AX7LPS do not have equal current draw in each filament. A wide variance will starve one side of the 12AX7 filament. These unbalanced tubes shows up on tube testers with unbalanced emissions that use 12.6 volts filament on 12AX7 tubes. The unbalanced 12AX7 filament draw can cause one channel to sound mildly or even extensively distorted.
Thus, if you purchase a load of these 12AX7LPS due to the low cost of re-tubing a Fisher, the phase splitters operate at 6.3 volts and in the case of the receivers, the phase splitters and multiplexer operates off of 6.3 volts. Use the unbalanced 12AX7LPS filaments in those positions. The unbalanced filaments will not matter due to the filaments are wired in parallel.
Perhaps the Russian Genelex Gold Lion 12AX7 long plate gold pin tube that sounds the same to me as the 12AX7LPS are factory selected for equal filament draw. However, the Genelex Gold Lion costs 2.5 times of the 12AX7LPS!!! (Ya, how about that 10 cent coffee, Starbucks is killing me!)
Long Live the King- FISHER