[Drake] RE: T-4XC Relay Problems Seemingly Solved

[Barry L. Ornitz]

Mike Murray, KW4HF, wrote:

> RE the posting below from 2 weeks ago...  I replaced
> the relay with a new one from Mouser, and all is well
> so far.

This was based on his earlier note:

> T-4XC Relay Problems
> My C-Line transmitter had been working well until
> recently when the relay started kicking in
> intermittantly, and it would usually kick back off on
> its own after a few seconds.
> I finally got a chance to take the covers off and
> replaced the V-9 MIC amp, V-10 VOX, and the V1 VOX Amp
> tubes. BTW, V10 is 6FQ7 on my schematic and owner's
> manual(1978 era) but the chassis and tube in my T4XC
> (serial #21068) are 6EV7 and that is what I replaced
> it with. Results? No change. I then made some gap
> adjustments (widening)to the relay based on advice
> that I had gotten, but now it kicks on and stays on.
> So, the symptom now is I turn the power on, and when
> the tubes warm up, the relay kicks on and stays there
> until I turn it off and there is a current reading on
> the meter... .25amps???. There is no output into a
> wattmeter and dummy load.
> I doubt the original problem was the relay, although I
> may need a new one now. <g>
> BTW, hitting the PTT switch on the mic yields no
> changes and no output. I am probably gonna put the old
> tubes back in, but thought you guys might have some
> advice, comments, flames, etc.

I am glad Mike solved his problem.  Filament to cathode leakage can
sometimes cause a problem here as can dried out electrolytics in the
VOX circuitry.  Another common problem, usually seen when the relay
will not drop back out, is the magnetization of the relay core from
the DC current through it.  If this problem occurs, a quick fix is to
reverse the leads to the coil.  Core magnetization is not normally a
problem with DC power relays, but this is a sensitive, high impedance
relay and it sometimes becomes an issue here.

        73,  Dr. Barry L. Ornitz     WA4VZQ     ornitz@tricon.net