[Amps] AL-80B Trouble

[pegasus at mho.net]

> Rich,
> Hundreds of empirical observations from all makes of amplifiers must be
> wrong. Clearly, the problems must be the mysterious parasitic
> oscillation, which obviously is pushing the filament sideways.

Let me offer a few empirical observation...
    Seventeen years ago... I received 3 year old SB-1000 (AL-80 in drag)
that had just been gone through by Heath factory and a new tube
installed.  About every 10th time I keyed the mic, "BANG".  Meters
pinned, especially grid current.  I was young and stupid.. used it
that way for few months, kept looking for evidence of a short
somewhere, never found it.  Pretty soon the tube was showing color on
only half the anode.  One side would be dark, other half cherry red.
(output was good though)   I called Heath, they sent me a new tube. 
(warantee)  Plugged it in, good even color, but amp still banging away
several times a day.  During a QSO another ham heard me describing
what was happening.  He most emphatically admonished me to write this
guy in California for the nichrome supressor kit or I'd lose another
tube in short order.  I'd never even heard of nichrome, but I ordered
it.
   From the moment I put that kit in the amplifier it has not uttered an
un-invited sound and is still with that 16 year old tube.

   Then only a few months ago I solved a long-standing problem with
another amp.  Never thought this was parasitic-related in any way. 
It's an AL-1200 I've had for about 5 years.  Whenever I'd run more than
about 900 watts there would be an arc in the bandswitch. "Pffftt" when
I'd tune up.  Problem occured ONLY on 75/80 meters. (and NO, I wasn't
underloading it)   I'd clean the switch up, had to repair it once,
re-solder, try to eliminate sharp points, etc.  Still would arc. 
Fortunately, I didn't use it much on 80 so it didn't bother me too
much.   Now at new QTH I wanted to use it more on 80 and not worry
about running high power. (no neighbors to QRM)  So I hand carried it
to a local ham repair shop.   He checked the switch again, cleaned and
re-soldered it, fired it up,  "Pfffttt".   He sniffed around and sure
enough found a strong 110.4 mhz oscillation around the tank circuit
when I was transmitting on 80 meters. (field seems strongest around 15
meter pi-section)  He pulled one of Rich's kits out of his stock on
hand, put it in, and the amp has never arced since.  He only cautioned
me not to use it on 10 meters... or run it at reduced power there.  The
suppressor also caused another anomaly to disappear.  Often when I'd
tune the amp on 80 meters the reflected power would jump slightly as I
tuned back and forth close to resonance.  Doesn't do that anymore.  I
can only assume that some of that VHF energy was getting up the coax to
and showing up at the meter when reflected.

   I've had 3 other amps over the course of that 17 years, they had no
problems and didn't have the nichrome suppressors.  Some do and some
don't.  I can't understand what the argument is about.  Why are some
people so afraid to admit this happens sometimes?  Twice now, I've had
the problem, and the kit fixed it.... period.   They might be
"mysterious" to a few, not to me.
Dennis
NØSP