[Amps] titan 425 dimming, dropping power

Jim Brown jim at audiosystemsgroup.com
Tue Dec 12 02:00:43 EST 2017

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

On 12/11/2017 10:12 PM, mike george via Amps wrote:
> 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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