[R-390] Gain drift

[hamfish at comcast.net]

Another thought:

The RF coil alignment, chapter 6 pg 6-16 Y2K R3. Are any of the slugs for
the RF section at the bottom range adjustment, ready to fall out of the
rack? If so one or more of the silver mica caps are failing. Usually this
only affects sensitivity of that octive (rack). 

So from what I'm reading if you were to check the IF gain for the -7  volts
at the diode load connections, it is changing? 

Craig, 

-----Original Message-----
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On
Behalf Of dog
Sent: Saturday, October 13, 2018 9:27 AM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] Gain drift

Thanks for suggestions. This is an EAC 1863 from about 6-67. I got it at
probably the Vienna or Gaithersburg fest maybe 20 years ago. Has all the
panels, most of the EIRC shields and is in not bad shape except for the hole
in the front panel and scratches. No mods. I've added a grounded plug to it
since last post, I was using one of those 3-2 prong adapters from an
extension cord. Now it's properly plugged in. All the usual suspect caps
have been replaced in the audio, RF, IF, PS sections. Not the 5000pf bypass
discs though. Been through it in the past for a major tune up and everything
worked properly and was in mostly in OK tune, IF section and RF both. But I
have this drop out issue. Last time the gain dropped I went through all the
tubes in the RF and IF sections to shock them to no avail, didn't try the
coils. Not sure if it happens in the MGC mode but probably, I've switched to
MGC and it's still there sometimes. I'll monitor the AGC voltage as said.
I'm monitoring the audio out of the diode load to get rid of the audio
sections, so it's not in the audio sections. It's almost like even static or
any signal will get rid of the attenuation where ever it's happening in an
instant, but shocking things does not seem to make any difference. It seems
to work fine with an antenna hooked up. AGC system works properly. Gain is
fine, 10DB S/N is less than 2uV. I can't measure it when the gain drops, it
always comes back. Also seems like once it warms up for an hour or so, no
problems.


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