I've got a few laying around somewhere. I've even got a new one in its
original sealed box. I'll see what I can locate.
I just need to figure out what they are going for now.
Lots of amplifier stuff for anyone looking for parts.
Jim Smith, KQ6UV
----- Original Message -----
From: "Paul Christensen" <w9ac@arrl.net>
To: <amps@contesting.com>
Sent: Sunday, October 06, 2002 11:47 AM
Subject: [Amps] Failed 8877
> After 20 years of service, I experienced my first problem with my Alpha
77Dx
> amplifier.
>
> I noted that the input VSWR into the amp was very high, zero plate
current,
> and only 40mA of grid current regardless of exciter drive level.
>
> I narrowed the root cause to a broken 8877 filament....although it was
> difficult to find beacuse it is intermittent. At the onset of filament
> current, it opens and after powering down the amp, and checking with a
DVM,
> the filamant resistance reads fine. I finally got it to read an open
> resistance right at the pins with the transformer Molex connectors
> unplugged. I can repeat the sequence and by putting the DVM in series
with
> the filament, I can see the DVM read AC current for a brief instant, then
> it goes to zero. When this occurs, I can then see the filament read open
> resistance right at the pins. Once I pull the tube and measure the
filament
> resistance, 75% of the time, I can then see good resistance. The other
25%
> of the time, it will read open. I do not have a spare 8877 at the moment.
>
> I'm not thrilled about a new Eimac replacement. Are there reasonable
> sources of good pulls with ample life? If so, where should I begin
looking?
> Thanks in advance.
>
> -Paul, W9AC
>
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