[Amps] Ten Tec Titan 425 Options

[Jim Brown]

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