I have a couple of 12DQ6s in my toolbox. I don't intend to use them as transmitting tubes because I have quite a few other tubes that will successfully fulfill that purpose. I am considering using these at low voltage to drive headphones through a transformer. Here is what I'm thinking...
- 12DQ6 in single-ended, parafeed mode.
- One stage of preamplification. NFB may be taken from output transformer to cathode of preamp triode. That will be if I need NFB. Preamp tube will be dual triode with 12v heater, not sure which yet. One triode per channel. Possibly 12SN7?
- Output transformer may be Edcor 15K - 600 ohm matching transformers (link below). With a 32-ohm load resistance, plate load resistance will look like 800 ohms.
- Supply voltage will be 30v. Filaments will be fed by constant current source transistors although no transistors will be in signal path.
The transformers are rated at 20-20KHz. I'll be using them in "parafeed", which means the transformer primary will be capacitively coupled to the tube plate and no current will flow through the primary winding. The 12DQ6 will have a resistor for DC current. If I idle the tubes at 15 mA each, that means I should be able to get 180 mW out of them into the 800 ohm transformer primary.
Questions, comments? I realize it's not an orthodox way to build a head amp but it's something I'm considering. I don't like buying high voltage parts and this seems like it would be something doable for a reasonable amount of change.