[Amps] Failed 8877

[noll amidzich]

Paul,

Try K9AU, Frank Stelloh for 8877 pulls. I have purchased from him. He is
honest and reliable.

GL

Noll  W9RN
----- Original Message -----
From: "Paul Christensen" <w9ac@arrl.net>
To: <amps@contesting.com>
Sent: Sunday, October 06, 2002 1:47 PM
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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