Re: {Collins} R388 TR Relay

----- Original Message ----- From: "George Babits" <gbabits@xxxxxxxxxxxxx>
To: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
Cc: "Collins" <collins@xxxxxxxxxxxxx>
Sent: Monday, July 22, 2013 7:00 AM
Subject: Re: {Collins} R388 TR Relay


Unless I am mistaken, the TR relay in the R-388 does not do a "full" mute. The receiver stays on with shorted antenna and reduced gain to provide a "sidetone." That was a military thing. Also, there are two versions of the R-388. One has speaker jack and a phone jack on the front panel. In the other version the speaker jack is replaced with a switch labled "Break In - -on/off). I have one of each. The one with the speaker jack I have installed in my shack and that provides a side tone. The one with "Break In" is my shop receiver. I don't know if it mutes fully or not and the manual copy I have does not address the 'Break-In" switch. I have never had occasion to apply 12 volts to the relay to see what happens. Anyway, the "not quite muting" that you are seeing is, I think, normal operation; at least if your R-388 has both speaker and phone jacks on the front panel.


The side tone is possible but the relay disables the third IF completely. I realized after sending my answer that it may not make sense. The relay in its normal position connects B+ to the third IF and connects the antenna to the bandswitch input. In mute it disconnects the B+ and disconnects the antenna and grounds it. It seems to me that not muting means the B+ is still getting to the IF stage even if the antenna is disconnected. That would not be caused by a dirty contact but might be caused by a couple of things including the relay not being energized or the contacts sticking in the operating position. Checking the plate and screen voltage at the 3rd IF stage would show if the contacts were not opening. I think the relay must be inspected physically to see if its actuating. If this is one of the receivers with a switch for the mute its possible the switch is not working. That can be checked by looking at the relay voltage at the switch. You can often clean bad toggle switches by squirting some Deoxit into the switch at the switch terminals, there is usually an opening to the inside. Toggle switches get dirty and intermittant pretty commonly especially if they are not often used. Of course one must also look at the solder joints at the switch and relay and also at the terminals at the back of the receiver. I don't remember if my R-388 mutes completely but can check it after work.

Richard Knoppow
Los Angeles

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