filter caps question

[dude]

My supply of Power filter caps has been sitting, new in my parts bin, some 7 to 8 years. I don't have a variac but never had a problem yet. I'm replacing a hard to find and costly Ampeg 70,40,40 can with single caps but the 80mf I have is about 7 or 8 years old but new. 

I guess a variac is the answer...? I have an a/c voltage reducer that slows down a 120a/c volt router, it does that by lowering the a/c wall voltage to the router, it has a dial . Could I use this, plugging in the amp through the device and lowering the ac voltage for a few hours at a times as I get to full voltage, recharging the caps...?

Thanks, al     

[Willabe]

This is what I have used.

http://www.electrojumble.org/reforming.htm

It did bring the caps leakage current down to below new specs if I measured correctly.

It takes a while time wise depending on how large the caps uF value is. The larger the caps value the longer it takes.

I have no idea if the caps will still have as long of a life as a new cap after being reformed.

The main point in his article is using a large resistance to limit the current as the cap reforms. Too much leakage current will heat up the cap and the electrolyte will start to boil and kill the cap before it can reform.


             Brad      

[dude]

Thanks Willable, but it takes time to make that board.

What are your thoughts on just recapping the amp and using the voltage lowering (router device) between the wall a/c and the amp?
The device has a dial and I can lower the current to say 50volts a/c to the amp to start, the PT will convert this to d/c and lowering the voltage to the filters according. After a few hours, turn the dial up to increase the a/c till I get to wall current, 120 a/c.

Seems like the only problem would be leaving the amp on for 20 hours or so, since the amp is diode rectified I could pull the tubes or on a tube rectifier leave that tube in pull the others.  Any more thoughts on this? If I'm "out to lunch" let me know.

al

[Willabe]

Thanks Willable, but it takes time to make that board.

Yeah, life's funny that way ain't it?        Time is money and money is time, which do you have more of?    

All you really need is the 2 R's on each end of the cap. The rest is not necessary. The 1K is for a good leakage measurement and the 33K could be more, 35K, 40K? It will just slow down the reforming a little.

If you read the article and study it a little, you'll figure it out.

As far as the "ac voltage reducer" I've not heard of it before.  

It may work but I have no idea. One of the other guys will know about it.


             Brad      

[HotBluePlates]

You were already gonna build a lightbulb limiter to perform a first power-up safety check and for future troubleshooting, right?

I'd just use a lightbulb limiter for reforming the caps. Leave the amp powered up using the limiter for some amount of time (whatever you deem necessary).

The end result of using a variac to reform caps is you apply a lowered supply voltage which limits the cap charging current somewhat. The reforming board uses resistors to limit cap charging current while reforming. And the lightbulb limiter restricts current delivered to the amp, doing the same job.

[dude]

Yes, I have a light bulb limiter and I've used it, saved me a lot of trouble when I powered up an Ampeg V4 head. That amp was the hardest amp I ever fixed but turned out great. I tuned it for bass with 6550's, my friend loved it.  The blub blew in a second at first fir-up, I had some things mis-wired. The limiter worked great, I was able to check all the voltages at a low voltage till everything was right, just used some math.

I fixed a lot of amps for friends usually from info on this site. I wish I could pay back but you guys are way more knowledgeable then any help I could give.

Hope my questions aren't pesty I know sometimes I ask questions and I already have the obvious solution but just not 100% sure. Just reading different posts are super informative.

Thanks all,

al