[Amps] titan 425 dimming, dropping power

Joe Giacobello, K2XX k2xx at swva.net
Tue Dec 12 12:51:17 EST 2017

Yes, indeed.  I had bought two used 425s many years ago, and while I 
don't remember the exact symptoms, I wound up replacing the P/S 
electrolytics in both of them.  I started replacing one at a time as I 
found faulty ones, but after that became a continual ritual, I decided 
to just replace all of them.  They're easy to replace because they're 
simply mounted and electrically connected with screws.

73, Joe

> Jim Brown <mailto:jim at audiosystemsgroup.com>
> Tuesday, December 12, 2017 2:00 AM
> I'd start by checking the string of big 450V caps in the HV section of 
> the power supply.  You want an old analog VOM, like a Simpson 260, on 
> a medium high resistance scale. First, disconnect from AC, make sure 
> the HV is completely discharged. Then use the VOM to go down the stack 
> (8 caps, I think) reading resistance, then reversing the leads, then 
> reversing again. For a healthy cap, you should see low resistance from 
> charging current, gradually dropping to zero each time you reverse the 
> leads. Go down the entire stack, remembering what the strongest caps 
> look like. Chances are you'll find only one that's weak, sometimes 
> two. While you could replace the entire string, it's rare that all are 
> bad. Buy replacements at the usual industrial electronics sources. The 
> last time I bought was ten years ago, think it was either Newark or 
> Allied.
> I've got three of these amps. Schematics that make troubleshooting 
> easier are on my website. k9yc.com/publish.htm  Scroll down.
> 73, Jim K9YC
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> mike george via Amps <mailto:amps at contesting.com>
> Tuesday, December 12, 2017 1:12 AM
> hi new to list hope someone can help with this. fired up the 425 and 
> noticed the 1500wts was down 3 or 4 hundred wts. looked at the rf deck 
> and the lights were dimming out on peaks.the plate and grid current is 
> ok but the plate voltage drops from 2200 to 1500 on peaks.i tried on 
> dummy load same result. other amp on same 220 outlet works fine on 
> same ant. i dont see anything obvious inside the power supply. tubes 
> are not getting hot. not sure where to go. thanks mike george
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