[BC] Collins 831F2 assistance needed

[towers at mre.com]

200ma of cathode current on a 4CX250 is a bit high.  I extended my tube
life by some margin dropping the current to 180mA.  I still obtain
sufficient PA drive at that level.  But that might also be a sign of
something else happening too.

Check the various coarse tuning controls and couplings to make sure all
the mechanical conenctions are clean, tight and good.  Also, the IPA
tuning belt will break.  Make sure that's OK and the cap is turning.

I have heard of the IP tuning cap going south too.

Also check the fine efficiency matcher if you box has that control.  The
open air cap can short and do all kinds of crazy things.

MM

> no, once I changed the tube, the resistor is fine, also ohm-ed the screen
> cap, no short
>
> I have good (200 mA) cathode current, which varies with exciter output, so
> I'm getting
> drive to the IPA
>
> I cannot, however, 'dip' the Ik with the 'Driver Plate Tuning' control,
> nor do I have grid
> current on the PA
>
> All this points to a coupling problem, but what ?
>
> From: <RichardBJohnson at comcast.net>
>
>>
>> The 4CX250 socket has a built in screen bypass capacitor. It is probably
>> shorted. That
>> would take out the series resistor.