[Amps] RE: Need Help

[Will Matney <craxd1@ezwv.com>]

Tom,
Ok this might narrow it down. If the squeal you hear changes tone when 
the step start kicks in, it's could be something in the HV side. If it 
does not, then that also takes us to the low voltage supplies, and self 
oscillation. If it is the HV supply, several things could cause this;

(1) A capacitor leaking. If so look for the rubber to be swelled up on 
it's end.
(2) A busted apart rectifier arcing across.
(3) Shorted transformer or winding arcing to the core.
(4) A bypass capacitor arcing
(5) A choke arcing
(6) A coupling capacitor (c block) arcing. If so the tune and load caps 
will be hot! This should blow the fuse.

The low voltage side for the screen and control grid, the same as above. 
If it's self oscillating, the high freq. RF could be arcing to ground as 
it cant get to the load (antenna). This happens most of the time at the 
load control between the plates or around the band switch contacts. You 
would notice it drawing plate current if it was oscillating. The last 
few places to look would be something wrong with the B+ safety switch 
arcing or a loose contact in the tube socket(s). It can arc around the 
finger stock in some sockets also, or a wire with bad insulation. I seen 
this on an old amp a while back. It pretty much had to be rewired around 
the B+ and screen supplies. Any of these wires close to the chassis 
could do this. The very first thing I would now check are those 
electrolytic capacitors. If one has ruptured, the relief will open in 
the rubber and will make a whining noise due to gas escaping, then an 
arc every now and then through the dialectic. This could explain the 
quick dip in the B+ meter.

Will Matney
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps