[Collins] Help 75A4

[Dr. Gerald N. Johnson]

On Mon, 2009-02-02 at 11:23 -0600, Larry Strong wrote:
> Recently purchased a 75A4 with speaker and manual and also with the 
> 35U-1 pass filter. Works good except the S meter. Flip the switch to Cal 
> and it works then back to on and works for a little while then quits. 
> Any help would be appreciated.
> 
> Regards,
> Larry Strong

Likely the switch has silver contacts. They oxidize and won't conduct
low voltages unless the oxide is broken down with higher voltage, like a
volt. I had that in my 51J-3. I replaced the switch with on having
precious metal (gold is good) contacts. No more problem.

Or it could be a bad solder connection in the S-meter circuit between
the switch and the tube.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer