>Hello,
>
>I have a TL-922 that has provided many years of good service. Sometime
>back, during a RTTY contest, when I unkeyed, the amp appeared to stay
>keyed (or partially keyed). I immediately (almost) shut the amp off. When
>I turned it back on after a minute or so, it blew one of the two fuses. So
>I turned it off again. Later I turned it back on and it blew the other fuse.
>
>I have physically examed the amp and I cannot easiily see any obvious
>damage.
>
>So I need to know:
>
>1. Where I might find the fuses or a suitable replacement. I live in the
>sticks of West Texas, so not much choice other than Radio Shack around here.
>
** Bill -- Mouser carries the fuses, but the problem wasn't caused by
defective fuses. My guess is that you had a parasite at c. 120MHz, which
caused a domino effect, which eventually blew the fuses. If I were
troubleshooting this amplifier, first I would measure the filament-grid
breakdown potential. It shoud be 5 - 8 kV. If it's under 5kV, the tube
may grid-fil short when lit. Such a condition puts a short on the +110V
PS., which produces 0v grid-fil bias, which causes plate/anode current to
flow during RX. Since the transformer that powers the filaments plus
the +110v cut-off bias PS, when a tube shorts in a stock TL-922, the
transformer will melt-down unless the power is quickly switched off..
There's an article about circuit improvements for the TL-922 on my
website.
>2. Does anyone have any idea what might have caused the problem to begin
>with and how best to proceed to fix it.
>
>Seems like it could be a stuck relay, but I can't tell by sight.
>
>Any help would be appreciated.
>
>Thanks,
>Bill
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