[R-390] R-390 Antenna Relay Chatter

[Les Locklear]

>From the "Archives"

DO NOT use the "STANDBY" position on the FUNCTION switch. The now unloaded stages will cause the various voltages in the receiver to rise upwards perhaps beyond the tolerances of some critical components. This is caused by the multiplicity error in our sometimes 120v+ line voltage v/s the 115v in use when the 390A was designed and built. Since it is normal for the "LOCAL GAIN" control to not completely mute the audio when turned down fully, it is natural to consider putting the receiver in "STANDBY." Remember, DON'T. Instead, turn the audio down and also back off the RF GAIN control to about 11 o'clock and the residual audio will disappear and no damage will be done to the receiver.

Les Locklear
________________________________
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf of David Wise <d44617665 at hotmail.com>
Sent: Friday, October 7, 2022 12:12 PM
To: Barry <n4buq at knology.net>; R-390 Mailing List <r-390 at mailman.qth.net>
Subject: Re: [R-390] R-390 Antenna Relay Chatter

Should not chatter.  #1 suspect is CR801; selenium rectifiers have a notorious habit of increasing forward resistance as they age.  Convert to silicon plus a resistor in series to mimic the natural forward resistance of new selenium.  (I don't know what that value should be.)  This is what Tektronix did with their oscilloscopes; for every selenium-powered model, they created a silicon retrofit kit.  One of my scopes has one.

Or you can add a reservoir capacitor, starting small and increasing until the chatter is reliably gone at low mains voltage.  I am using 100uF.  Upside is potentially reduced hum.  Downside is that CR801 will continue to deteriorate, so eventually the problem will recur.

HTH,
Dave Wise
SWL (inactive)
________________________________
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf of Barry <n4buq at knology.net>
Sent: Friday, October 7, 2022 9:59 AM
To: R-390 Mailing List <r-390 at mailman.qth.net>
Subject: [R-390] R-390 Antenna Relay Chatter

When in STANDBY, the antenna relay in my R-390 produces a bit of chatter.  Is this normal?  I see where that relay is fed, unfiltered, from CR801 which, from the pictures in the manual, appear to be a stack of selenium diodes and I'm wondering if that rectifier stack might be a problem.  Anyone know what to expect from that relay in STANDBY and, perhaps, what I'm seeing might be normal?

Thanks,
Barry - N4BUQ
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