>
>Just got a new to me Alpha 76AE. Yesterday 1 of the 8874's seemed to
>short on startup....
This could be caused by loose gold-meltballs. I would use a high-pot.
tester to see whether gold-sputtering is the problem. If it is, there is
a simple procedure for moving loose gold meltballs into the base, where
they won't cause arcing. Typically, this procedure improves emission.
end
>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
>
>--
>FAQ on WWW: http://www.contesting.com/FAQ/amps
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>
>
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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