As the owner of a dead TL-922 I figure I should add a few observations....
>
>History was:
>
>Amp was in retirement for 3 yrs after 3yrs of trouble free use. It had the
original Eimac tubes in it.
>
>Powered it up 2 weeks ago, it failed instantly with a loud bang while in
standby (in CW position). Lost both 15A fuses as well as the grid choke and
resistor for V1. The output was connected to a cantenna and a 30W 50 ohm
load was attached to the input.
>
>Checked both tubes by applying 0 - 1800v from plate to filament and
voltage applied to filament. V2 had no problem, but the whole inside of V1
would light up from gas with as little as 800V (Color was roughly pink to
magenta). Subsequent visual check also showed that the fil. was fractured.
It may be a coincidence that the tube went gassy over time *and* the
filament failed, but the amp was never bumped or dropped so I suspect that
the cause of the filament failure was the current surge through the gassy
tube. It's possible that disassembling the tube could reveal more about the
cause of failure, but the gas inside lights up so nice I want to keep it as
a display piece :)
>
>As for the zener:
><insert>
>That was the basis of my question last week; what goes first, the choke
>or the zener? Thank you for repeating it.
><end>
>
>The zener in my amp checks good, so the choke went first. Also, in
standby, the filaments are connected to the cutoff bias supply so in a
standby bang the zener should not be affected. In the schematic it looks
like the zener only provides operating bias.
>
>Questions:
>
>If I replace the grid chokes with fuses, should I leave all the bypass
caps in place?
>
>Any easy to deal with mail order tube suppliers out there that publish
prices? Here in Canada there doesn't seem to be a 'Tubes r-us'.
>
>Thanks,
>
>Steve Parsons
>VE3SMP
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