The output impedance of EF183 triode connected with 1.6MΩ from anode to grid and 12V anode potential is less than 5KΩ

For more details please see the nearby post on the Pleiades Electra III part 2.


This came up while investigating the use of electron tubes as output stages using small anode poetical by a battery.


For even lower noise and use of electron tubes as top quality front end microphone preamplifiers for example the following conditions where preferred.


EF183 triode connected. Cathode to ground. 3.9MΩ from anode to grid to free electrons. 3.6V for heaters. 3.6V for the anode circuit. A 10KΩ anode resistor. Or an output transformer. The input impedance is 100KΩ. The anode current of the order of 100μΑ. Output impedance 50KΩ? The signal is capacitor coupled to grid.


See also Pleiades V4, V5, V6 preamplifiers.


The output of V4 for example is connected to a medium impedance mic input. One would expect hiss and noise coming from the second preamplifier output. Yet it is so quiet, there is doubt whether the V4 is off or on. When a microphone is connected with an input transformer the signal is so loud, clean, dynamic, low noise, the subtlest detail of voice is revealed.


A reason for the ultra low noise operation may be the very low potential minimizing secondary emission effects from all electron tube elements.


The output impedance of the EF183 at such conditions sould be around 50KΩ?


Reference:


Operating features of the Audion - Edwin H. Armstrong


On preserving transconductance of an electron tube at anode potential as low as 3.6 volt - euroelectron blogspot


Schematics of Pleiades V4, V5, V6 pre preamplifiers - euroelectron blogspot