[Collins] 75S3 PROBLEM

billriches bill.riches at verizon.net
Wed Feb 3 19:31:48 EST 2016


Hayseed has cans to fit.

73,

Bill, WA2DVU

-----Original Message-----
From: Collins [mailto:collins-bounces at mailman.qth.net] On Behalf Of Dr.
Gerald N. Johnson
Sent: Wednesday, February 03, 2016 6:26 PM
To: collins at mailman.qth.net
Subject: Re: [Collins] 75S3 PROBLEM

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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