[Collins] 75A-2 question

[Dr. Gerald N. Johnson]

On Thu, 2007-08-23 at 15:06 -0400, jeremy-ca wrote:
> Has it ever been recapped and out of tolerance resistors replaced?
> Then replace weak tubes and do an alignment.
> 
> Once the receiver is brought back to factory specs those problems will most 
> likely go away. Or at least give you a valid place to start measuring the 
> AGC action and make changes if necessary.
> 
> At one point I thought that my 75A4's were above the ills that only the 
> "little radios" (A take off on Leona Hemsley) suffered. Once I went thru 
> them I was amazed at the improvement.
> 
> Carl
> KM1H
> 
> 
> 
Yup a little leakage on a screen bypass lowers the screen voltage and
that lowers the gain. Do that to all the RF and IF stages and a little
leakage hurts the receiver sensitivity quite a bit. Then that added
current in the screen resistor makes it run warmer and drift faster,
usually going higher in value lowering the screen voltage but increasing
the power dissipation in the resistor.

Old electrolytics also go bad, faster the smaller they are.

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer