[Collins] Fwd: 30l-1 f`ilament center tap

[Dr. Gerald N. Johnson]

On Mon, 2009-06-01 at 10:32 -0400, drleborgne at aol.com wrote:
> 
> 
> -----Original Message-----
> From: drleborgne at aol.com
> To: collin at mailman.qth.net
> Sent: Sun, 31 May 2009 3:00 pm
> Subject: 30l-1 f`ilament center tap
> 
> 
> dear Collins aficionados:
> I resort again to your wise advice: My 30l-1 burned 2 ant relay coils, but I cannot find anything else defective.,although there is no PA current unless I gnd one of the filaments terminal.?The circuit diag shows a center
> tap to gnd , however this one does not have one .? Any wise suggestions?
> ?Martin KI4JRY
> 
The relay coil should be rated at 110 volts DC. It should have that 2K
resistor R12 in parallel with the coil.

Has this a replacement plate transformer? Are you putting 240 volts on
the 120 volt primary? Yes the schematic shows a center tap on the PA
tube filament winding. Has wire white green red. That means white
insulation with wide green and narrow red stripes. What is the voltage
on the -120 volt point with the PA not keyed? Too much voltage there
could be hard on the relay coil. But it might be accompanied by higher
filament voltage on the 811A which is not good for their longevity
either. The PA tubes are biased off with that -120 volts through the
relay coil. Check for loose grid wires inside the tubes, maybe one of
them is shorting plate to grid. Maybe the 47 ohm resistors at the grids
are scorched.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer