[ARC5] Use of a Variac

[J Mcvey]

The only ancient electrolytic caps that I ever ventured to save is the oil type. Sometimes the seal can be repaired and refilled..  The dry type just get changed.
When bringing up a radio in unknown condition, I check for obvious short issues with a DMM before applying power.I use a 60 watt incandescent light bulb in  series with the line. This does a pretty good job of current limiting and is a visual indicator of the current being drawn. After the initial current drawn by the caps charging, the bulb should be dim. If the bulb stays bright , there are issues. if the bulb is bright at moment the switch flipped on , in a tube set, the transformer may be bad or has a short in or across a winding.
I don't have the patience to try reforming caps that may or may not respond to treatment.
    On Thursday, April 23, 2020, 7:25:40 PM EDT, Mike Feher <n4fs at eozinc.com> wrote:  
 
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Most of the reforming I did, I used my time. I would start at a low voltage at a comfortable current like about 5 ma and then wait and do something else. Come back to it and if the current went down I would increase the voltage for the same current, and so on. I kept it up till I reached rated voltage. Sometimes I gave it about 8 hours on average. If I was able to reach rated voltage, I never had a problem with that cap again. Most of these were WWII vintage. Resting current when done was a function of capacitance. 73 – Mike 

  

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

848-245-9115

  

From: arc5-bounces at mailman.qth.net <arc5-bounces at mailman.qth.net> On Behalf Of Mark K3MSB
Sent: Thursday, April 23, 2020 7:09 PM
To: Robert Nickels <W9RAN at oneradio.net>
Cc: ARC5 <arc5 at mailman.qth.net>
Subject: Re: [ARC5] Use of a Variac

  

Hi Bob

  

Very nice video.   To test capacitors I do pretty much the same thing with either my Heath capacitor tester or HV power supply and some meters.   You have nudged me to build a meter box like you did.

  

What I cringed at was you reformed a 30+ year old capacitor.  It worked for a few minutes.    What kind of longevity testing have you done?    Say after 100 to 200 hours at rated voltage?     

  

I still have to philosophically disagree with capacitor reforming.   I feel that the availability of new and inexpensive capacitors make reforming unnecessary,  and provides a more robust solution.    If I'm rebuilding a transmitter,  I would simply not feel good about putting in 30+ year old caps (reformed) when a short after hours of operation can take out something made of unobtainium.

  

Mark K3MSB.

  

  
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