Just got a new to me Alpha 76AE. Yesterday 1 of the 8874's seemed to
short on startup....
Before I invest the $ on a new tube< I would really like to knwo the
cause....can
this just happen occasionally or ??? Here is the full story.
Got the amp home and after inspecting it internally and removing a
relatively small
amount of dust, I fired it up and it owork fine .... about 600 Watts out
on 40 through 10
Never tried 80 or 160 at the time. In the next couple of days, I fired
it up and it
worked fine. Took it off the desk for the contest last weekend...run LP
because of
neighbours and sat it on the floor. Put it back on the desk last night
and hit the
on button and that's when the troble started... I found that in lifting
the heavy beast
I had depressed both the cw (lp) and SSB (hi) voltage buttons. On start
up it took out
R2, 1 20 amp fuse and the slow blow fuse which protects a couple of
relays on start up in
case of mistakes on faults which prevent another relay from closing on
start up (so the
manual says).
Replaced R2 (a 10 ohm /12 watt) resistor, the fuses and tried again.
The relays would
chatter but not engage. After speaking with Glen at Alpha, I replace a
filter cap that
is part of the 28 V circut and removed the tubes, fired it up and the
power supply came
up just fine. Relpaced the first tube and every thing worked fine
again. Added the second
tube (its a 2 tuber) and we were back to blowing fuses, however a HV
crowbar condition
which was exhbited by the failure of R2 did not occur.. just blew one of
the 20 amp fuses..
it is wired for 120 still... Then I swapped the bad tube to the other
socket and it still blew
the fuse. Runs fine with just the one good tube. Glen at Alpha did not
seem to think that
depressing both HV buttons on start up would case the problem anyways.
So here is the question... Anyone else had this same problem with both
hi and low power
buttons ij by mistake on an Alpha 76 or similar amp before? Will the
tube just sometimes go out,
like has been suggested... these pair of tubes are apparently very
new... the older
gentleman I bought it from is quite trustworthy. If one does short as
described would it take out
the HV crowbar....it would seem to make sense. What else should I look
for in the amp... don't
want to waste another tube.
Anyone got a good 8874 that they want to part with?
Many Thanks
Sam
VE5SF
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