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Beefing Up Power Supply Caps [message #21178]

Fri, 15 August 2014 13:14

Jerrybass1955
Messages: 45
Registered: August 2014
Location: NC

Member

While I am repairing my pawn shop K100-2, I thought I might up the value of the power supply filter caps to tighten up the amp and max out my headroom. I have some 10,000 uF caps on order along with a 25A bridge rectifier that I plan to install.

Although I haven't checked out the power supply except to measure the voltage and ripple when I first opened the amp up (Seemed Perfect, but of course no load since it isn't working yet), the original caps look pretty good and appear to work just fine with no load. Assuming they are OK, anyone have an opinion on whether I should just leave them in and parallel the new caps up with them, or should I just get rid of them. With 45 years history, just seems like a good idea to get rid of them, but then again - if they are still working well, why not keep them in until there is a sign of problems. Any thoughts or opinions? Obviously these are quality caps but 45 years is a long time!

Also, am I likely to have problems with fuses blowing after this upgrade? If so, any suggestions on the best way to solve that potential problem?

Jerry

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Re: Beefing Up Power Supply Caps [message #21180 is a reply to message #21178]

Fri, 15 August 2014 13:38

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

There is no set rule about changing filter caps, or at least in my opinion there shouldn't be. Age alone is not the only indicator as to the condition of the caps. I've read and debated this question here and at other forums and there are compelling arguments for both sides of the topic. I feel that each case is different and calls for different approaches depending upon the specifics of the situation.

The only suggestion that I will make to you, is as long as the power supply is currently working, do not change anything until you cure the other problems first. Repair first and then modify. It can make your life much simpler.

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Re: Beefing Up Power Supply Caps [message #21182 is a reply to message #21180]

Fri, 15 August 2014 14:07

Jerrybass1955
Messages: 45
Registered: August 2014
Location: NC

Member

No question it is always good to repair first then mod.

I am 80% sure the repair is done, but have to put the amp back together before I will know 100%. Ran out of time last night after getting done with replacement of a bad transistor. But since the mod is in the plans and parts are ordered I wanted to get input from others so I can figure out how best to proceed. Planning is half the fun!
Jerry

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Re: Beefing Up Power Supply Caps [message #21188 is a reply to message #21182]

Fri, 15 August 2014 23:29

C4ster
Messages: 686
Registered: June 2001
Location: Mukwonago, WI (Milwaukee...

Senior Member

The only rule I use when deciding to change/not change filter caps is; "how long does the hiss take to drop out after turning off the amp". If the hiss goes away almost immediately, replace. If the hiss lasts more than 2 or 3 seconds, no. That's it!
Conrad

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Re: Beefing Up Power Supply Caps [message #21191 is a reply to message #21178]

Sat, 16 August 2014 01:22

daveobergoenner@gmail.com is currently offline

daveobergoenner@gmail.com
Messages: 104
Registered: January 2007
Location: Missouri

Senior Member

In my K200, the caps needed replacement, but the problem only really showed up when the amp was trying to make full power into 4 ohms. At idle, all seemed normal. Even driving 8 ohms all seemed pretty normal. They even measured good for value and ESR.

Changing them to new, higher value caps make a considerable improvement in the "puchyness" of the amp when playing bass up near full power. I went to 15,000uf in my K200.

C4ster's advice on how long the hiss continues is a very good one...that, and if you are not hearing any hum problems. You may, or may not notice an improvement. A lot depends on how hard you push it.

Big filter Caps are expensive, and if one doesn't have suitable replacements on hand, see how the amp is actually performing for you when playing through it. The original caps Kustom used in these amps were VERY high quality, and in many cases, they may be performing nearly as-new, even after 40 years.

It sounds like you have some 10k caps in stock, so you might try changing them, and see if the investment seems to make sense. In my case it did. But I run the amp near full power, all the time, playing bass. Guitar generally does not load an amps power supply rails so hard.

Just my 2 cents worth,
Dave O.

Dave 0 Wall-O-Bass
Webpage - <a href="http://webpages.charter.net/daveobieone/" target="_blank">http://webpages.charter.net/daveobieone/</a >

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