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Old February 25th 10, 06:24 PM posted to rec.radio.amateur.boatanchors
Richard Knoppow Richard Knoppow is offline
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First recorded activity by RadioBanter: Oct 2006
Posts: 527
Default National NC-88 questions


"Bill M" wrote in message
...
I'm working on an NC-88 and a couple things aren't sitting
right with me.

1. Overall 'oomph' seems to be missing. It receives well
enough but even benchside listening requires that the
volume be up to about 75%. Doesn't seem right. An AA5
would blow it away. Finger on the volume pot wiper gives
a very healthy hum so the problem must be further back.

2. BFO. Works but is really weak. I tried more coupling
but no increase. The Sensitivity control has to be almost
at the floor to hear it. Its really too weak to be
functional.

Recapped, many resistors found out of tolerance, voltage
checks are all ok. Some previous owner had the IFs badly
mistuned. Found an intermittent factory joint on the
bandswitch.

I guess what I'm asking are these 'features' typical of
the NC-88? I wouldn't think so. Maybe the two symptoms
are related?

Thanks for any comments.

-Bill WX4A


All of this points to something in the
detector/avc/noise limiter area. Have you made tube socket
resistance measurements and voltage measurements? Those may
show something up. When doing extensive recapping there is
always the chance of getting something in wrong or one of
the new caps being bad.
While the BFO voltage is generally low in conventional
receivers its not _that_ low and should give a strong beat
note with the RF gain in normal position although it will no
be linear enough for SSB.


--
Richard Knoppow
Los Angeles
WB6KBL