[NJARC] Bring it up slow on the VARIAC

[Islandradiosvc at aol.com]

The Variac is a nice tool to slowly bring up voltage on a set.. This alone  
does not equate to the electrolytic capacitors being slowly brought up to  
voltage. It also does not tell you much, about current draw. To start with, 
you  want an ammeter on the load. The only Variacs that I have seen , that 
have this  feature built in, are the Eico and the Sencore.  Even if we add an 
 ammeter  in series with the load, it does not tell you what the capacitors 
 are doing. Obviously if an 8 tube set, is beginning to pull 4 amps, we 
have an  issue, but something that drastic is not usually the case. Also, bear 
in mind  that because of the warm up characteristics of rectifier tubes, the 
filter  caps may not see voltage until it is high enough to damage them 
without  reform. If you choose to re from the electrolytics, I suggest using a 
bench  B+ supply, capable of reaching working voltage, along with a digital  
multimeter to monitor the current draw of the capacitor being re-formed. In 
my  experience, a healthy cap, (in the 5-60 mfd range) after re form,  
should NEVER pull more than 3 or 4 ma. You slowly bring up the bench  supply, 
across the cap, with the meter in series, and watch the current, you  will see 
it spike, then begin to fall. each time it falls below 4 ma, raise it  
again, say 60 volts at a time, but never let the cap pull more than 50 ma. When  
they pull huge amounts of current, is when they destroy themselves. Better  
still. Eico  and Heathkit, and others made capacitance bridges, with built  
in power supplies. These are very lightweight supplies, only capable of  
supplying a few MA.. They are IDEAL and rather foolproof for re-forming, Their 
 lack of available current, prevents them from damaging the capacitor, and 
you  can simply hook them up, and let the cap sit for 20 min. or however 
long it  takes. Again, I place the MA meter in series, and watch the current 
fall. IF you  find an electrolytic will not stop leaking current, within a 
reasonable amount  of time, I say toss it. It is simply not worth the risk. 
Also... I make it a  policy to re check current draw a day or 2 after reform. 
If the capacitor does  not act like a  new capacitor (or at least close) and 
takes an extended  period of time to stop pulling current, again.. toss it. 
I have seen too many  "re-formed" capacitors fail suddenly and take a power 
transformer or costly  rectifier tube (or both) with them.  We are reaching 
a point where this  stuff is OLD.. I am finding more and more electrolytic 
capacitors , particularly  those from the 1950s and before , that are 
reaching the end of their useful  life. 15 or 20 years ago, these capacitors seemed 
much more willing to re-form  and and stay formed. From what I have been 
able to tell, capacitor technology  changed vastly in the 1960s, and hence 
electrolytic capacitors made from that  point and later, seem to fair better, 
and they are also newer. Also Sprague,  Mallory ,Astron and a few other 
electrolytic  capacitors seem to survive  vastly better than some other brands.  
Just my 10 cents on all  this...  Used to be 2, but we can calculate for 
inflation... 
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