[Collins] 75S3 PROBLEM

[Dr. Gerald N. Johnson]

I believe there are sources of a replacement C59. Knepper should know 
where. I know that its been removed, cut open and new guts installed.

In my 75S3B, I found some angled nose diagonal cutters and cut the three 
lugs from the capacitor leaving the multiple wires connected to them. I 
found a piece of Vector board or Radio shack prototype circuit board 
with individual solder pads at 1/10th inch centers but no through hole 
copper and cut a piece to fit between the cut off lugs and the old 
capacitor and soldered the freed lugs to the pads on the circuit board 
being careful not to short the lugs together. I bought capacitors from 
Mouser with suitable ratings and with both leads on one end. Radial was 
the description. I soldered one to that assembly at C59, and the other 
two at a post of lugs toward the front of the radio to be at 
appropriated places in the circuits but just not concentrated at the C59 
location. Its been a while so I don't remember every detail. Looking in 
my manual, I surely put at least one at C59 probably for the middle 
section, one at the turret with CR1 and CR2 for the input capacitor, and 
one over on the turret where R14 and R15 connect together. Something 
like Panasonic ECA-2EM470. Not exactly orginal but it works.

With that much ripple I'd think there would be hum from the speaker. Be 
sure there's no heater cathode leakage in the BFO tube, and that the 
negative bias filter capacitor is good including the low voltage one on 
the bias lead to the audio output tube. C60 and C29. Ripple on the bias 
or AC from heater cathode leakage will be 60 Hz while B+ ripple will be 
120 Hz because of the full wave main rectifier.

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

On 2/3/2016 3:06 PM, Ed - K9EW wrote:
> I have a 75S3 with a raspy-sounding audio tone when receiving CW.  It looks
> like it must be from the 4.4Vpp of ripple on the B+ line, so that means
> replacing the triple-electrolytic C59.  (I've already replaced the other
> electrolytics in the hope that one of them may be the culprit, but the
> raspy CW note persists.)  It looks like a tedious job to replace it, so I'm
> wondering if someone knows of an easier way to do this than removing
> several parts just to get to the terminals of C59.
>
> Do you replace C59 with three discrete electrolytics?  Where do you put
> them / how do you mount them?
>
> Or can you rebuild C59?
>
> Or, is there a direct replacement for C59?
>
> Thanks in advance for any suggestions.
>
> 73,
> ed - k9ew
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