Re: {Collins} R388 TR Relay

Given that this relay may have been sitting for decades without being operated, cleaning the contacts is a "must". An accepted procedure is to apply DeOxit to a business card or similar and slide it back & forth between the contacts.

Occasionally, particles will collect between the armature and the pole piece, preventing the relay from operating fully. So you should slide a business card in there as well.

It's unlikely that the relay will need adjustment -- but it should be checked. As you push down on the armature, the "break" contacts should open first, then the "make" contacts should close. This should occur just a bit before the armature contacts the pole piece. This bit of "follow" is built into the relay so that some contact pressure is developed, and so that the contacts "wipe" against each other, which helps to keep them clean.


On 2013-07-21 11:57 PM, Richard Knoppow wrote:

----- Original Message ----- From: <ka4koe@xxxxxxxxxxx>
To: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
Cc: "Collins@xxxxxxxxxxxxx" <collins@xxxxxxxxxxxxx>
Sent: Sunday, July 21, 2013 8:11 PM
Subject: {Collins} R388 TR Relay


Wired up the TR relay with an external source of 12VDC. Relay actuates as it should, but the radio does not mute fully, or not at all. Does this sound like a symptom of dirty contacts in the relay???


Sounds like dirty contacts. I think this is an open frame relay so it should not be difficult to clean. There are two sets of contacts; one switches the antenna from the input bandswitch to ground and the other switches the +210V buss going to the plate and screen of the third IF tube. You should be able to see the voltage change at pins 5 and 6 of V-109. The relay in my R-388 works quite reliably on 9 volts and mutes the receiver completely.

Richard Knoppow
Los Angeles


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