Hello all,
I am looking for explanations for an occurrence with my
TL-922. Let me state a couple of things up front, because
this could easily become another endless thread about
parasitics.
1. This amp has had every known mod on the Rich
Measures site done to it already. Don, KI6SZ, did
the modifications. Thanks to Don and Rich for their
help/contributions.
2. After the initial mods were done, I suffered another
grid short on one of the tubes. These tubes are the
3-500ZG's from RF parts. After getting and re-installing
another set of tubes Every thing has been FB for about
four months.
Well, maybe... Yesterday, I had tuned up as usual into
the dummy load at about 14.240. So far so good. I answered
a CQ at 14.310 without the amp, again so far, so good.
Conditions were fairly bad, so I put the amp on line at
about 500 watts. Again, OK. But, when I upped the
power to full, about 1200 watts or so, I heard a POP!
Followed by the sound of my voice coming from the
amp and accompanied by a bright white light.
Not good... Upon examination, I found that the two 1-ohm
resistors that are part of the new parasitic suppressor had burned.
This suppressor is formed from nichrome wire and forms a
series-parallel network.
I replaced the resistors, and re-installed the suppressor.
Apart from an initial sput or zap sound from the amp, all
seems normal. After the initial zap sound, I did remove and
inspect the suppressor, suspecting that I might have burned
another resistor, but it looks normal. I also installed another
3-500ZG to check against the first. This was done to see if
the initial tube had developed a fault. So far so good. I then
re-installed tube number one and tuned the amp on 10,15 and
20 meters. Power out, plate and grid current, HV, input SWR,
all appear OK.
So now to the 64 dollar question: Was this just some kind of glitch, or
was I visited by the dreaded VHF parasitic demon?
Should I just keep on operating until something else fails, or
should I beat the rush and run screaming into the hills?
73 Gary, WG7X
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