[Collins] Great information

[Dr. Gerald N. Johnson]

It is pretty good but misses one crucial thing to repair in the 516F-2 
power supply, the selenium bias rectifier is way beyond its working life 
and is putting AC on the bias supply filter capacitor which is hard on 
the capacitor and also has a lot more voltage drop than it did when it 
was new and so the bias supply dependent adjustments, like RF gain and 
PA idling current are way off. Also little details like receiver muting 
while transmitting and transmitter muting while receiving and during 
transitions.

All users of the 516F-2 power supply should have already ripped out the 
selenium rectifier (true for early 75S receivers too) and replaced it 
with three terminal soldering strip and a silicon rectifier like a 
1N4004, 1N4005, 1N4006, or 1N4007 (increasing PIV, the 1N4007 is often 
easiest to find because it works so universally). A poor bias supply 
(rectifier and electrolytic capacitors) in the 75S receivers, especially 
those without a cathode bias resistor on the audio output tube make the 
audio output tube run even hotter tha normal and can fry the tube and 
sometimes the special audio output transformer and that transformer is 
an expensive repair item.

A 6AQ5 in place of the 6BF5 will reduce the heat of the audio output 
tube, but seriously reduce the available audio power from 2 watts down 
to about a half watt.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 1/29/2017 3:20 AM, David Knepper wrote:
> http://www.ccae.tm6cca.com/DOWN/CCAE-SOMEKWM2TRICKS.pdf
> You have to bookmark this site.
> David Knepper - W3CRA/W3ST
> Collins Radio Association
> www.collinsradio.us
> Join the CRA today