>The bias is controlled by two zener diodes (controlled by the CW/SSB
>switch). Does toggling the switch make an appreciable difference in the
>resting current? Most likely, you have a damaged zener.
>
>It doesn't sound like you had an oscillation; it sounds like you had an arc
>from plate to grid,
** Agreed, but anode(plate) to grid arcs are typically the result of
loose gold particles , not a ceramic-metal seal leak. According to
Eimac's 8877's development team, gold migration is the result of an
"oscillation condition" (letter of February18, 1986). For those with a
high-potential tester, determining whether an envelope has air leakage,
due to a bad seal - or gold evaporation leakage, due to an oscillation -
involves applying (+) and then (-) polarity HV from the anode to the grid
(the Funderberg test). If the leakage current is the same with both
polarities, air leakage is the problem. If the I-leakage is more with
positive polarity than negative polarity, the leakage involves gold
particles. Also, loose gold I-leakage can be reduced by tapping on the
top of the anode, but air I-leakage can not.
> or maybe a power surge. I've found these will take out
>the grid resistors, zener, meter etc.
** If a power surge did such damage, would not the HV-filter caps have
been zapped? To me, kaput grid resistors mean there was an anomaly in
grid current.
>
>Sorry you're having such lousy luck.
>
** Murphy would not agree that luck is a factor.
>Ed N1TS
>----- Original Message -----
>From: "Dana Roode" <K6NR@ARRL.net>
>To: "AMPS" <amps@contesting.com>
>Cc: "Dana Roode" <K6NR@ARRL.NET>
>Sent: Saturday, November 22, 2003 12:36 PM
>Subject: [Amps] AL-1200 Questions
>
>
>> Folks -
>>
>> My AL-1200 repair efforts continue. As you may recall, the parasitic
>> suppresser came unsoldered and I had some sort of oscillation in the grid
>> that took out the grid resistors, a resister in the grid meter, and my
>> 756ProII. It turns out it also took out my ARB-704 relay buffer, and last
>> weekend the grid meter mechanism itself gave up the ghost.
>>
>> Questions:
>> - After replacing the grid resistors, the resting plate current seems too
>> low, maybe half of what it should be. Is there an adjustment for this?
>I'm
>> not sure why it would have changed.
>> - I will order a new meter, should I put a diode across it to protect it
>in
>> the future? What kind?
>>
>> Dana
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