It may be possible by using a high Megohm resistor from plate to grid as is done on the Pleiades V series preamplifiers.
On a previous post the principle was mentioned as a Pleiades V6 preamplifier was used to drive 150 ohm headphones through its output trasformer.
The influence of the 8.2MΩ resistor to free electrons was tested and made a dramatic difference. When it was disconnected the 100μA anode current dropped to almost zero and sound almost became inaudible. this is because without it the grid self assumes a high negative potential, typically hundreds of -millivolts which restrict the passage of electrons to the anode at low anode voltage.
Cathode was connected to ground as usual.
The sound quality was beautiful but more power is needed.
Power supply was 5.8V for the anode and aproximately 3V for the heaters.
Further experiments need to be done.
It may prove possible to connect 300Ω headphones directly to the anode without an output transformer.
Changing to 12V as is used in other Pleiades Electra headphone amplifiers may make a lot of difference in power output and lowering of output impedance.
A 12SK7 gives perhaps more than 1mA at 12 Volts with the trick of positive grid neutralization.
Other candidate tubes can be 6SK7, 6K7, EF86, ECC82, E88CC...
On a previous post the principle was mentioned as a Pleiades V6 preamplifier was used to drive 150 ohm headphones through its output trasformer.
The influence of the 8.2MΩ resistor to free electrons was tested and made a dramatic difference. When it was disconnected the 100μA anode current dropped to almost zero and sound almost became inaudible. this is because without it the grid self assumes a high negative potential, typically hundreds of -millivolts which restrict the passage of electrons to the anode at low anode voltage.
Cathode was connected to ground as usual.
The sound quality was beautiful but more power is needed.
Power supply was 5.8V for the anode and aproximately 3V for the heaters.
Further experiments need to be done.
It may prove possible to connect 300Ω headphones directly to the anode without an output transformer.
Changing to 12V as is used in other Pleiades Electra headphone amplifiers may make a lot of difference in power output and lowering of output impedance.
A 12SK7 gives perhaps more than 1mA at 12 Volts with the trick of positive grid neutralization.
Other candidate tubes can be 6SK7, 6K7, EF86, ECC82, E88CC...
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