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[Amps] Al-811 Troubleshooting

Subject: [Amps] Al-811 Troubleshooting
From: chris lorantfy <>
Date: Thu, 18 Sep 2003 19:41:56 -0400
List-post: <>
Hi Gang,
    I'm having some trouble with my AL-811 and would appreciate some
advice.  It worked fine the last time I used it, and I shut down
normally.  However, now the 12A fuses on the AC input blow as soon as I
try to turn it on.
    Two of the tubes have a shiny deposit & their filaments measure 0.5
ohms.  The third tube only a smokey appearance, no shiny deposit, and
its filament reads open.  I don't have much experience with power amps,
but I'm guessing that maybe the one tube had been bad for a while and I
was driving the two good tubes excessively hard. Shouldn't there have
been an increase in the drive requirements?
    I have new tubes on order, and my primary question is : Are there
any checks I should do now, before just plugging in the new tubes?  It's
not obvious to me why the tube problem causes the line fuses to blow.  I
thought about trying to turn on the amp with the tubes removed to see if
the fuses would be OK, but I'm worried the plate connectors hanging
loose might short to the chassis.  Any comments to help me understand
the problem?

Chris VA3NR

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