(drum roll please
.....)
AND NOW, LADIES
& GENTLEMEN, THE MOMENT YOU'VE ALL BEEN WAITING FOR ...
Ok, enough hype, on
to the real post.
Last night I
finished my cap replacement in the R4A. I replaced the PS filter cap
module and, while I was at it, the handful of paper caps that "should oughta be
replaced". I also put in new blue filter material.
Overall, the
replacement process was fairly easy. My R4A is a 13 tube model which only
used 3 of the 4 caps on the new filter cap module which was fine. The
effort went smoothly, although it did take a few hours.
Prior to the
replacement I saw a few small issues with the receiver. There was some AC
hum in the audio. CW tones were a bit raspy (not really noticeably on
SSB). The RX background tended to modulate up and down just a bit as did
signals. RX audio had a bit of a narrow sound to it with limited lows and
highs, regardless of the PBT setting. Also, there is significant loss in
the .4 position but I didn't expect some cap changes to affect
that.
Once I changed the
caps, I turned the rig on and was quite happy to have no smoke! Like a
teenager in the morning, the radio slowly rose to life. I give it a few
minutes to warm up and then started listening using
headphones.
I still have some DC
on the audio but it is not as strong. I think this is just the way these
rigs are as my 2B also shows some DC on the audio. The slightly raspy CW tone is
still there. The narrowness to the sound is still there as well.
The slight
pumping of the gain seems to be gone.
I have some hope the
narrowness to the sound and the loss in the .4 position are both related to PBT
alignment. I may do some o-scope signal tracing to see if I can find when
the CW tone goes from clean to raspy. Hopefully this is just an issue with
a tube.
- Keith KD1E
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