This simple technique can be used on the Pleiades V series electron tube battery microphone pre preamplifiers or the Pleiades Elektra no component headphone battery powered electron tube power amplifiers.
It assures gradual turning on or off without glitches, transients. This is the most sensitive and perhaps important part of a sound recording system. The front end amplifier. Anything wrong happening here will be subsequently greatly magnified by the rest of the system.
The battery is always connected to the anode circuit.
There is no current flow as the cathode is cold.
A switch supplies power to the heaters.
The cathode temperature begins to increase and the low noise amplifier comes to life.
It also serves as a check. If when switching off the heaters the signal to noise ratio starts to increase it means that the cathodes must be made even more underheated.
These circuits are operated deliberately at lower cathode temperature. For example the EF183 original designed for 6.3V may be supplied by only 3.7V.
Underheated cathodes take more time to make the amp operate.
Same as on the Neumann U47 or the AKG C12A microphones.
One has to wait many seconds for electrons to start flowing from cathode to anode to have sound beginning to coming out.
And one can hear the miracle of nature, the sound coming in and noise gradually almost disappearing.
Great fun.
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