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
On 11/21/05, Jason Buchanan <[EMAIL PROTECTED]> wrote:
"Jason Buchanan" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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hi,
I fired up my beauties tonight but noticed the receive on the R-4B is not as
hot as it used to be. Receive sensitivity doesn't seem to pull 'em in like
it used to. It's good but doesn't seem great like it used to be. Received
CW notes have some hum in them - it's not bad but it's not pure and clean.
Listening to the same stations with my Omni 6 proves that the hum is in the
R-4B and not the sending station.
The AC-4 has some hum in it as well listening to the sound coming from the
cabinet.
Just wondering what everyone might recommend for either/all of these
problems. I'm pretty handy with my weller soldering station but I have no
idea where to start debugging problems with the R-4B especially. I could
replace the caps in the AC-4 but wondering if there's more than just the
caps that I should replace. And also wondering if that large can in the
R-4B should be replaced.
vy 73 Jason N1SU
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