How should I wire 2 tubes in series, in way to supply 12ax7 with 12v (shouldn't be using H tap pin), and one 6dj8 with 6v? Am not sure if simple series wiring will work for a 19v suppy. I am worried it will apply 9v to each equally.
12AX7 at 12V needs 150mA, 6DJ8 needs about 330, so no, this will not work. But, you could use 12AX7 strapped to 6.3V, that would be 300mA and a PCC88 equivalent (series heater equivalent of 6DJ8) also at 300mA in series connection, and that would require about 113.5-14V. Best would be to use a higher voltage and a series resistor to get less dependance on mains.
You could also use a resistor in parallel with the 12AX7 to match current of the 6DJ8 but then you have the problem of different heater characteristics, you will get varying currents during heat-up. A current source for heaters would help a little. The resistor in parallel with 12AX7 heater would be about 70 ohms, 68 is the closest 5% standard value but should work OK. The only thing is you are wasting power by conversion into heat on it, about 2.3W, so you need a 5W resistor at least. You may need to trim it a bit to get the right voltages.
You could also use a resistor in parallel with the 12AX7 to match current of the 6DJ8 but then you have the problem of different heater characteristics, you will get varying currents during heat-up. A current source for heaters would help a little. The resistor in parallel with 12AX7 heater would be about 70 ohms, 68 is the closest 5% standard value but should work OK. The only thing is you are wasting power by conversion into heat on it, about 2.3W, so you need a 5W resistor at least. You may need to trim it a bit to get the right voltages.
6DJ8 - 12AX7 Filaments
xZur & ilimzn,
I am not sure what I am missing here but, why not tie pins 4/5 together on the 12AX7 and run the tube at 6.3 volts? A 12AX7 is designed to operate at either 12.6V (pins4-5) or 6.3V (4/5-9). In either case the tube requires ~300mA to operate both halves of the filament. In this case you would simply run the 6DJ8 and 12AX7 filaments in parallel - provided your supply could provide 600ma-700ma required for both tubes
-ALBQ
6DJ8 - pins 4-5 (6.3V only)
12AX7 - pins 4/5-9 (6.3V) pins4-5 (12.6V)
xZur & ilimzn,
I am not sure what I am missing here but, why not tie pins 4/5 together on the 12AX7 and run the tube at 6.3 volts? A 12AX7 is designed to operate at either 12.6V (pins4-5) or 6.3V (4/5-9). In either case the tube requires ~300mA to operate both halves of the filament. In this case you would simply run the 6DJ8 and 12AX7 filaments in parallel - provided your supply could provide 600ma-700ma required for both tubes
-ALBQ
6DJ8 - pins 4-5 (6.3V only)
12AX7 - pins 4/5-9 (6.3V) pins4-5 (12.6V)
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