[BC] Collins 831F2 assistance needed

[Milton R. Holladay Jr.]

Beware: I have seen one of these xmtrs kill the exciter due to a fault in 
the driver causing a damaging voltage to back up into the exciter. Be sure 
to have a 1/4 wavelength shorted coax teed onto the driver in/exciter out 
and perhaps add a 1000pf doorknob in the driver input to block any DC from 
gettinng to the exciter, as well.  ( I suspect that it is one of the air 
variables arcing over that causes this problem, but never got to the point 
of resolving it.)
Was this the one with a rubber-ish belt on the driver tuning, or was that a 
later version ? Beware of broken belt or loose shafts. Be sure no sliders 
have slid.
Six watts from the exciter should be all that is needed when everything is 
right.
Sounds like an example of multi-factorial causation.. Let us know what it 
really is............
M

----- Original Message ----- 
>
> On 6/7/09, Gary Glaenzer <glaenzer at verizon.net> wrote:
>>
>> found burnt 47-ohm resistor in 4CX250 screen circuit
>>  changed it
>>  it burned again
>>  changed again, and changed driver.
>>  STILL no PA Grid current, but now have good (215 mA) Cathode current on
>>  driver
>>  'Driver PA Tuning' will not dip cathode current
>>  no PA grid current
>>  changed final, same readings
>>  any thoughts ?
>>    Gary