[AMPS] TL-922 FILAMENT TRANSFORMER starting to smoke...

[Ian Procyk]

Hello all,

Our local club station VE7SCC, has owned and operated a TL-922 for the
last 13 years.  We bought the unit new in the late 80's and it has been
working quite FB until about 3 months ago.  

At that time, I began to notice that the output power was not arriving
instantaneously, but rather creeping up to it's normal 1KW in about 3-4
seconds.  The steady climb is noticeable even when operating phone.  The
dummy load and watt meter confirmed my observation. Note: This can be
duplicated over and over with various rigs, each time when the tubes are
allowed to "cool" and sit idle for 30seconds between tests.  The
metering both on the external Bird and the internal TL-922 IP meter
indicate the slow rise in output.???  

Over the last month, during normal SSB operation it has been noted that
one tube seems to be working harder then the other, visually getting
much more red when drive under normal conditions 60watts and with meager
voice processing.  The filament also seems *slightly* brighter on the
tube that is drawing more current.

The real reason for writing this message is because of a subsequent
filament transformer failure.  About a week ago, while the amp was
idling, I and several others heard the amp emit a small "crack".  At
this point the filaments having been on for over 1 hour and the amp had
gone without use for over 30 minutes.  The smell that filled the room
was not easily identified but later through an autopsy it was revealed
that it was emanating from the filament/bias transformer.  We removed
the 3-500
S and started the amp up again, all interlocks defeated, we stood back
and watched, NO smoke, so we assumed that the problem has occurred on
the secondary of filament winding.  When the tubes were put back in, the
problem came back and we could hear the windings cracking with heat.

After all is said and done, I would like to know if anyone else has
experienced similar problems and if they could provide any insight.  

In the end it would also be helpful to find someone who knows where a
replacement filament/bias transformer can be found for the TL-922.





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