Jason Buchanan <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Dennis Monticelli wrote:
Hi Jason,
I also noted that CW notes were hum modulated in my R4B. Because you
remember better performance in the past, perhaps the big can is going
south on you? I have only worked on two Drakes (a 4A and a 4B) and
both of them needed can replacement. Post replacement, both radios
still had finite residual hum, though much improved from before. My
R4B is no longer modulating CW notes. After a doubling of the
capacitance of the first filter section, the hum is now inaudible.
See my earlier post regarding the 4B and Garey's suggestions for
alleviating headphone hum.
Look for a bulge in the PS can or a hotter than normal can or
excessive ripple on the filter sections. The first filter section
(across the raw DC) is hammered by the most ripple current and can be
expected to fail first due to localized heat buildup. If the measured
voltage ripple is much more than about 8Vpp, it should be replaced.
While you're in there, I would replace the other (less stressed)
sections at the same time.
Denny AE6C
hi - thanks for the advice. Can you point me in the right direction of
the components I should replace? The big can near the transformer is an
obvious one (although i'm afraid it won't be replaced with one that is
so pretty looking - these new can electrolytics are black and ugly hi)
but I don't know what others I should target. I can solder well, just
not sure what other places will need to be retooled inside the R4B.
Same for the T-4XB but I think i'll take care of the biggest problem
areas with the AC-4 rebuild.
Thanks,
Jason
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