On 11/8/2012 8:39 PM, Gary "Joe" Mayfield wrote:
A little over a year ago I acquired a working Ten Tec Titan 425. It spent a
year in the closet as I had nothing to load it into. I finally got the new
antenna up and turned on the amplifier. After about 30 minutes the fuses
popped and the amp was dead.
I took it to Burghardt Radio Repair and Jim said the transformer was good,
but most of the rest of the supply was toast. I believe him as he has
always been fair and square with me.
He said there was a mod that added another diode to each leg of the bridge
that probably would have saved me. I paid him for the diagnosis and brought
the amp and supply home. The bad news is the caps alone are around $800.
Other parts, labor and I am probably looking at $1200 or more. I don't have
that kind of cash and if I did I'm not sure this would be the most effective
way to spend it. So, I am trying to figure out my options.
Any suggestions?
I have three Titans, two of which I've done enough repairs on to sort of
know my way around them. I'm an old time ham, and an EE, so I can work
on them myself. If you are in that category, the amp can be fixed for a
LOT less that $800. If you are not, your best bet is to sell it to
someone who IS in that category. The 425 is a very nice amp, very well
designed, and it's worth fixing.
Several details.1) It is common for some faults to fry a few traces on
a PCB in the power supply. Once the cause of the fault is fixed, those
traces can be rebuilt with wire.
2) The big filter caps in the high voltage string can be obtained from
standard sources like Allied and Newark for about $40 each, and it is
quite rare that ALL need to be replaced.
3) You can get a good handle on which caps are bad by testing each
individually with a mechanical VOM (that is, one that has a pointer) on
the Ohms scale. A good cap will show lots of charge/discharge action
when you place the leads on the cap, then reverse them. A bad cap will
show little action or a short.
4) The source of the fault is likely to be in the control circuitry for
keying, which is on a couple of circuit boards underneath the tubes.
They are easy to remove but tricky to reinstall, easy to troubleshoot
with a simple VOM, and repair parts are all generic, inexpensive, widely
available discrete transistors and diodes. The key to reinstalling them
easily is to tape the screws that mount them to the chassis so that they
don't fall out.
5) There may also be a fault with one of the tubes. Once you've worked
through steps 2-4, if you still blow fuses I'd pull the tubes and sell
if the fuses still blow. And for testing, I would use a 15A fuse in one
of the sockets and a 30A fuse in the other. The two fuses are in
series, the 15A fuse will blow more quickly and minimize damage, and
you'll save money on fuses. The only reason for fusing both sides of
the line is to protect against faults in the transformer or other
components on the primary side of the transformer. If it doesn't blow
fuses with no tubes, try installing one at a time.
6) There's a detailed schematic of the Titan 425 on my website that
helps with troubleshooting. It covers everything in detail except the
bandswitching in the RF deck. http://audiosystemsgroup.com/publish.htm
73, Jim K9YC
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