Re: [TenTec] Titan 425 problems

["Ron Castro" <ronc@sonic.net>]

It's been awhile since I have had any serious problem with my 425 with the 
exception of a fuse that just decided it was time to die.  I replaced it and 
all has been well since.  In the past, I did have a problem with the bias 
control board which burned itself up, most likely due to a lightning strike 
or some other event.  I simply replaced the whole board with a new one from 
TT ($61.88 according to my notes) and that fixed the problem.
Other problems that have arisen over the years included the plate 
transformer shorting (took out the diode board, too), which was a fairly 
common problem.  Shortly after it was returned from the factory for that 
work, a disc capacitor on the HV meter shunt board got too close to the 
chassis and blew up.  I replaced all the caps with better ones, stuffed the 
board and bent the components so that there was maximum space to the 
chassis.  I replaced the rubber grommets in fan body and mount to quiet it 
down a bit.
Other than pilot lights, that's all that's gone wrong since 1989.  Still 
running on the same finals with 2kW key-down output!  It's reduced to 
standby use since I got an ACOM 2000A in March, but it was pressed into 
service a couple of months ago when the ACOM quit and had to go east.
        Ron  N6IE
     www.N6IE.com


----- Original Message ----- 
From: "David J Windisch" <davidjw@cinci.rr.com>
To: <tentec@contesting.com>
Sent: Sunday, October 14, 2007 2:44 PM
Subject: [TenTec] Titan 425 problems


> 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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