Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Dan -
OK. Well we have a broad range of experience on here so I usually start
out simple! :-)
V9 and V10 are only used for the NB. V9 (12BA6) is the Noise Amp, and
in the later "B" version is AGC controlled. The NB switch only grounds
the cathode of the IF shunt section of V10 (12AX7) so really doesn't
change anything else. You could try pulling V9 (all filaments are in
parallel) and then switching on the NB. Pulling V10 doesn't really
prove anything since with it out, the NB switch doesn't do anything
other than hang a high resistance voltage divider across the +150 line.
I haven't seen any consistent problem with the NB circuit, although
Drake did make some changes to the AVC control of V9, indicating there
may have been a problem. Does signal strength seem to have any effect
on the problem?
The only thing that comes to mind is that the 12BA6 is prone to gas or
grid emission, and the 12AX7 at V10 does sometimes have heater-cathode
leakage issues. Pulling and then perhaps substituting those two is
where I'd start.
What is the s/n of the unit you have? The AVC change on V9 was made at
s/n 10501. The NB circuit was unchanged otherwise through all versions
from s/n 7000 on.
One more "off the wall" thought. The switch tag that turns on the NB is
right next to the tag that turns on the calibrator. The calibrator puts
out a nice strong signal at 50 kHz, right at the third IF.
Contamination of the gap by spray contact cleaners, or a worn drive hole
in the switch wafer may let it go just a little bit too far? (I SAID
it was off the wall, but in 45 years of working on Drake gear I've seen
more than a few off the wall problems! :-)
Let us know what you find!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Daniel J Wright wrote:
Daniel J Wright <[EMAIL PROTECTED]> made an utterance to the
drakelist gang
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Garey Barrell <[EMAIL PROTECTED]> made an utterance to the
drakelist gang
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Sorry if this is something you already know, but we gotta start
somewhere! :-)
Thanks Gary!
I should have explained it better, but first I had to get someone's
attention! <grin>
The audio on my R4B is just fine until I turn the function switch to
NB. It's not
because the noise blanker has any noise to blank. The roughness
actually sounds
as if there is an extra carrier inserted. You know how audio sounds
when you approach zero
beat? The "normal" SSB audio has a character like it's almost at zero
beat. I hear a beating
in the audio, I guess you could say. Since everything else is normal
when the function
switch is in ANY position other than "NB", I am assuming that whatever
circuitry is switched
in to do the noise blanking, is causing the problem.
I can troubleshoot this. I can read schematics just fine. I have been
a broadcast engineer
for over 35 years, and a licensed amateur for 43 years. I don't know
everything of course,
hence my questions. I was just wondering if anyone had this experience
with their R4Bs.
I'm lazy and thought someone could tell me how to fix it!!!
I'll have two nice R4Bs for sale soon if anyone is interested.
Thanks a bunch es
73 de Dan -- WA0JRD ..
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