Hi, all concerned:
This amp was built in 1994 or 1995, according to TT's service dep't. It sat
apparently unused for years: no wear spots, no dings, no scratches, no
finger jam anywhere, no tracks on bandswitch contacts, no silvery pilot
lamps, and so on.
When I fired it up for testing, the QSK was inoperative. This first repair
effort was my initial contact with TT manuals and sorta-schematics*. The
schematics omit parts and leave out nomenclature on some of the parts they
do show. It took an effort to trace the QSK circuit out, going from board
to board, and another effort to figure out just how the QSK works, even with
the sorta-explanation in the manual. The eventual solution was to unwind
an end-turn on an opened RF choke, and splice it.
Second attempt at testing produced a bodacious BANG, from the amp deck, I
think, and the primary fuses were toast. Didn't figure out what caused that
bang. Replaced the fuses, and powered up without further incident.
For the first year or so, I operated the amp on c-w at the low-voltage
setting with 1500W out, and then, after another bodacious BANG followed by
RF power drop-off to about half, I went to the high-voltage setting to get
back to 1500W out again. Didn't find anything amiss -- at that time,
anyway.
There happened later another bodacious BANG, which turned out to be the
traces to the step-start resistor in the power supply simply vaporizing. I
replaced them with #12 jumpers.
Last week, the power supply produced a couple more bodacious BANGs.
I pulled it apart, and found a popped filter cap, which I think is C6. I
noticed that one of the two resistors in parallel with C6 is 150 ohms, not
150K like all the others. The step-start resistor was also burned open, and
the soft-start fuse was blown.
TT quoted $35 a pop for the filter caps. They're available at better prices
elsewhere.
I removed the cap and jumpered its connections. Fired it up again, got HV
OK, but the meter pegs in the grid-current position and the red OVERDRIVE
lamp illuminates. Same after removing the tubes.
While looking into that, I noticed what may have produced the bodacious BANG
followed by power dropping, mentioned earlier: there had been an arc and
carbonization where the plate RF choke plate-side lead was run (too) near
the middle of the choke body. Wire-brushed the choke body windings, and
they looks OK under magnification.
Any one out there have any ideas about the grid meter problem? I've
searched the archives on "titan or 425" and seen nothing except that it
happens.
TIA & 73, Dave,
N3HE
*Afaik, I have the matching manual.
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