RCA 4117A
- Thread starter bluesbaz
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bluesbaz
Well-known member
volume control..... arrg nevermind......
dmp
Well-known member
It might be a meter / test point for voltage check
The 41b had test points brought out to the front panel to check the tubes.
The 41b had test points brought out to the front panel to check the tubes.
My understanding is it's a voltage-controlled amp. Signal input on G4, gain control on G1.bluesbaz said:
I would think the switch arm is the period term for wiper. It seems the term is still used for wire-wound rheostats.
This is my reading. A remote knob/pot adjusts the 1612/6J7 gain. 6J7 is supposed to be a self-oscillating converter which can take AVC, for AM radio front end. ("Pentagrid"; in Europe: "Octode".) One grid is very remote-cutoff to tolerate the spread from 50uV out of Denver to 500,000 Watts out of Cleveland (US kitchen radios needed much wider dynamic range than in Europe).
Here signal is put to grid 3 (the usual signal grid). A varying voltage tapped from large cathode resistor bleeder is fed to G1, and reduced to G3. The operating point is far outside the data, but extrapolating it would give large audio gain wiper up (away from ground) and much lower gain (<-40dB) wiper down. ~~1Meg impedance and C-3 on control voltage mean the pot may be "any distance" from the preamp without trouble. I'm guessing pot should be more than 33K but less than 1Meg; 250K a likely choice.
Here signal is put to grid 3 (the usual signal grid). A varying voltage tapped from large cathode resistor bleeder is fed to G1, and reduced to G3. The operating point is far outside the data, but extrapolating it would give large audio gain wiper up (away from ground) and much lower gain (<-40dB) wiper down. ~~1Meg impedance and C-3 on control voltage mean the pot may be "any distance" from the preamp without trouble. I'm guessing pot should be more than 33K but less than 1Meg; 250K a likely choice.
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Heptode.PRR said:
