Before we had this "amps' reflector I had no amplifier problems and no one
to ask if I did. Now I have both.....
Alpha 77D (says PA-77 s/n 2986 on the rear)
Symptoms.... After 3 min warmup, attempting to drive the amp only produces
maybe 50ma of grid and no plate or RF out. The exciter shows infinite SWR.
So far, repeated cycling (3 minutes each time) and/or a hard left hand jab
has brought it back to life, where it has performed flawlessly for the
next 48 hours. (it's done this in 3 contests in a row now). The 77 has
been doing fine here for many years, this is just a recent hiccup.
I have not taken the lid off yet. Looking at the schematic, input relay
K4 and output relay K5 have their coils in parallel - K5 must switch but
K4 isn't - but once K4 starts working, it stays working all weekend. And
if K4 isn't closing, how do I get some grid to flow? Grid current is low
for the drive applied, but then the exciter is cutting WAY back due to
SWR. If K5 was bad, why would the input SWR be so hi? If they're both
bad, how come it starts working and then behaves perfectly? So many
questions...........
Any one had this happen, or can offer any insight?
73 Don
VE6JY is Don Moman email: ve6jy@freenet.edmonton.ab.ca
Box 127 Lamont, Alberta
T0B 2R0 (403) 895-2925
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