TJM wrote:
Why do you say that it looks like the relay is fine? Have you tested
its contacts? Have you looked at its contacts? Just because it goes
kachunk doesn't mean it is doing its job. Every symptom you have
described
is classic for T/R relay contact problems.

Hi Chuck,

I guess I should have been more specific...I pulled the relay.

I had pulled the relay and looked at it ( it's new as the tr4c was newly
rebuilt when I rec'd it ). took a few readings and all was ok without
power of course.

Anyway, I re-pulled the relay (thank goodness for sockets) and poped off
the plastic cover...
Using an old elmer trick for keys, I used a strip of a dollar bill and
some alcohol. After doing all the contacts, put back in.

Well, you were right! I just got done testing it and it looks good for
now... time will tell... no more problem after 15mins or so.

Thanks agn

Hi Tom,

I have seen this problem many many times. The relays have contacts
that were designed to run at several amps, and we are using them for
microamps in some of these circuits. The contacts would self clean if
enough current was passing through them, but how much current do you
really need to switch a crystal oscillator from USB to LSB? A proper
signal relay would have gold plated silver contacts to help prevent this
problem. WECO relays used in the phone system were actually made so that
each actuation would make the contacts wipe against each other.

A dollar bill is made out of really terrific paper. It should be excellent
for cleaning contacts. I used to keep some cotton bond typing paper around
for the job, but laser printers have rendered such nice paper obsolete.

With any luck, you won't have to clean the contacts again for a couple
of years.

-Chuck