----- Original Message -----
Sent: Tuesday, August 08, 2006 9:33
AM
Subject: [drakelist] R4A cap replacement
- prelim results
(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
-
