Corollary to a previous issue with a B+ transformer I passed thru the group
a while back, which before I repaired it had a current loop due to bad/no
insulation on the core bolts. Transformer has a 240V primary, 2800-3000V
secondary rated at 2 amp CCS. Is installed & in use on a HB GS35b 6m amp.
When "module" testing the amp the transformer taps met specs, measured with a
Simpson 260. Calculations based on measurements then indicated a 12.5 to 1
ratio.
Fast-forward to completed amp...After some occassional use (~30 minutes of
total operating time) am having the following "issues." The 3000VAC secondary
tap is now only putting out 2700VAC with line voltage measured at 243VAC (240V
mains line is 10 guage wire, a 10 ft run from the breaker box & then 6 feet of
12 guage line to the amp... original measurement taken with same lines). The
even more disconcerting problem is that after a couple hours of sitting at
"idle" (amp on, power to B+ but no RF) the transformer iron is getting hot-
enough that you wouldn't want to keep your hand on it for long, and
particularly so near the left & right sides of the core. (Yes, I checked the
plate meter & no current thru tube, bias relay fine).
Lamination bolts remain cold so no more current loop around the mounting
brackets.... I am baffled as to why this thing is getting hot just idling.
There is no "bleeder" per se on the PS, just 6 x 220k ohm Rs across each of
twelve 450V caps in series. The only other constant current draw is a 5 MEG
dropping R to the B+ meter. I am baffled as to why the transformer laminations
would get hot with almost no current draw, and am concerned that once I really
work this thing out during a contest or Es opening the heat is going to short
the secondaries.
Any ideas as to what could be going on? Is this normal, or as I am
beginning to think, an 86 lb misdesigned piece of junk??? Any input appreciated.
73 Dave N3DB
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