The 1H4 grid becomes -600mV (50mV measured from negative filament terminal when filament is 1.3V) and plate voltage 9V. the sound is fine on a mic booster preamplifier. It operates very nicely at such conditions. But it does not operate at 1.5V at all even with pull up or Pleiades bias. More experiments are needed.
The 7586 grid space potential is many hundred millivolts negative when heater is 3.9V and plate voltage is 9V. But it operates greatly even with 1.5V at plate with pull up bias or Pleiades bias. Put differently how high does plate potential have to be on 7586 with free grid for a great mic booster sound?
Is there an electron tube that can operate with 4V to 9V anode potemtial with free grid or grid at space potential? Giving about 20-40μA?
The 1H4 has not been tried yet at 4V.
The CV2269 has not been tried yet at higher than 1.5 Volts.
The EF183 triode connected has not been tried at open grid and 9V for example.
The 12SK7 triode connected has not been tried with grid at space potential.
The UCC85 has been tried with good results at 48V with free grid. see Pleiades V(-1)?
The ECC82 has not been tried yet with grid at space potential.
Why free grid?
It seems to give a free, easy and big sound.
See also previous today's posts.
See also Open-Grid Tubes in Low Level Amplifiers - Meyer - Electronics - Oct 1944
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