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 8:58 AM
Subject: Re: {Collins} R388 TR Relay

I know that the 12 volts is getting to the relay when I transmit. I also know that I get a sidetone. This is the receiver without the Break In switch. If I put the receiver in standby, it is shut off. If I use the mute relay I ahve a sidetone. I suspect that the break-in switch may have been added to defeat the sidetone and allow for full muting. It would be best if someone could look at a schematic of the models with the break in switch. That would tell the story. Until then it is all speculation.

The early R-388s were designed for diversity operation. Power for the "remote" terminals which control the relay came from the diversity unit, which is shown in my manual. The manual doesn't have anything about the "break in" switch which must have come later. By the way, the R-388 in my shack with sidetone has a navy tag on it. Great for monitoring your transmitted keying on CW.


The relay seems to be the same regardless of whether there is a front panel switch or not. Mine has the switch. I tested using a 9 V battery to actuate the relay and put a very strong signal into it from a grid dip oscillator. This was strong enough to overload the receiver. The muting was complete, no side tone or any detectable signal with the mute on. If you trace the "stand-by" switch you will find it is in series with the mute relay contacts and turns on and off the same voltages. What it does _not_ do is switch the input to the bandswitch going to the RF from the antenna to ground. So, if the stand-by switch completely mutes the receiver but the mute relay does not it suggests that the mute relay is not breaking the B+ voltage its supposed to switch. If it leaves that up but shorts out the antenna its possible there will be some feedthrough or perhsps the voltage is dropped but not cut off. The voltage at the 3rd IF plate and screen should help tell the tale. The front panel mute switch, where it is present, opens the circuit from the rear terminals to the relay coil. Its possible that if this switch or its wiring have high resistance the mute relay may not pull in all the way. One can guess all over about this but an inspection of the relay will soon tell what is really going on.

Richard Knoppow
Los Angeles

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