Re: VTTC grid leak

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bob (R.A.) Jones" <a1accounting-at-bellsouth-dot-net> 





 > Original poster: herwig.roscher-at-gmx.de
 >
 > Bob,
 >
 > Increasing the grid leak resistor from 680 Ohm to 50 kOhm lead to an
 > increase of the grid bias from - 25 V to -145 V.

Wow 74 fold change in R for a 5.8 change in bias

 >
 >  > Assuming no break out. I would have expected the total swing to
 >  > decrease because as you increased the negative bias the anode swing
 >  > should decrease.
 > - Without breakout the control signal is 370 Vpp and with breakout it
 > is 550 Vpp.

I guess that's the low Z top high Z in and high Z top low in bottom thing.

 >  > Put say a 1 ohm resistor in the cathode circuit to monitor  the
 >  > current.
 > - Unfortunately the cathode of the 4-125A is heated directly i.e. the
 > filament current of 6.5 A ac would flow through the resistor as well.

Not if you put it in the ht return connection.

 > I will try to monitor the plate current instead.

Assuming the grounded side of the ht is the cathode side that will make it
difficult to monitor with a scope.

 >
 > As this circuit provides automatic level/bias control, I now
 > understand, why it is so difficult to amplitude modulate it. The
 > modulator tries to change the amplitude of the signal and the
 > oscillator tries to keep it constant.

Yes that's right if its in class C.

Bob Jones