[Amps] TL-922A - Loud Pop, Blown Fuses

[Clay Curtiss W7CE]

Thanks for the responses.  I didn't think about an internal tube short as a
possibility.  I removed the plate caps from the 3-500's and the HV  measures
normal (2100V CW, 3100V SSB). Is it logical to assume that one (or possibly
both) of the 3-500's has developed an internal problem or should I be
looking for other causes as well, such as a bias supply problem.  I don't
have access to a hy-pot tester, but a simple resistance check from filament
to grid on both tubes doesn't reveal a short.

One thing I didn't mention earlier (because I don't believe it's relevant)
is that the small filament choke (L20) that connects to the filament
transformer center tap, has overheated in the past.  Since one of the tube
filaments came unsoldered from the pin (a simple soldering job fixed it),  I
figure all of the extra current flowing through the small choke was the
cause of that.  Other than some discoloration, it appears ok.

Any and all suggestions are welcome.  I don't want to risk my power supply
by blowing more fuses trying to determine which of the tubes might be at
fault.

73,
Clay  W7CE


----- Original Message ----- 
From: "K7RDX" <k7rdx at earthlink.net>
To: "Clay Curtiss W7CE" <w7ce at curtiss.net>
Sent: Saturday, December 04, 2004 5:42 PM
Subject: Re: [Amps] TL-922A - Loud Pop, Blown Fuses


> Hi Clay, pull the tubes and start the amp again. If plate voltage is
normal
> and the fuse doesn`t blow again, shut everything down and inspect the tube
> sockets for burnt or damaged rf chokes from the three grid pins to ground.
> If one of the tubes flashed over, some of  these chokes will probably be
> destroyed or at least damaged. 3-500z tubes sometimes develop a short from
> grid to filament after a period of use and will flash over on the next
> start-up. If you have access to a hypot tester, a shorted tube is easy to
> spot...Hope this helps you find the problem...A flashover might damage the
> bias as well as the high voltage supply. 73,Jim.
> ----- Original Message -----
> From: "Clay Curtiss W7CE" <w7ce at curtiss.net>
> To: <amps at contesting.com>
> Sent: Saturday, December 04, 2004 12:05 PM
> Subject: [Amps] TL-922A - Loud Pop, Blown Fuses
>
>
> > Yesterday morning when I turned on my TL-922A, there was a very loud pop
> > followed by blown fuses.  I replaced the fuses, changed the setting to
CW
> to
> > reduce the B+ voltage and tried again.  Similar result with several
> smaller
> > pops and then blown fuses.  I use a footswitch for T/R control and it
> wasn't
> > depressed nor was I transmitting with the exciter when I powered up.  I
> > should also mention that I've heard a pop on power up two times
> previously,
> > but neither time caused a blown fuse.  I opened it up today for a visual
> > inspection and see no signs of arcing or anything unusual.
> >
> > Before I dig into this thing, has anyone else experienced this problem?
> Any
> > hints or suggestions to reduce the troubleshooting time will be
> appreciated.
> >
> > Thanks and 73,
> > Clay  W7CE
> >
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