when to use a variac

bookasan

Appassionato circa audio
Ok, I am not very experienced in the world of tubes. I first got turned on to vintage audio when I was given a complete Altec tube system about 8 years ago. My Grandfather bought it new in 64' and it included an integrated amp, tuner, multiplex, speakers and a gerrard turntable. I later sold it and made a bundle. I was then hooked on the whole audio thing. Almost all I have collected has been S.S., but I have just added an H.H. Scott LK-48 amp and Lt-110 tuner to my collection.
I have seen various threads about using a Variac to fire up tube amps, but when is this necesary?
I can't imagine having to use one every time you use it.
Is it only a good idea when you replace tubes or when you first build an amp or.......?
 
My real basic understanding is that the caps deteriorate from not being used and the layers need to be reformed by the gradual application of current. I believe that you use the Variac for the initial application of current when staring up a long idle unit; once it's been done, the caps should be OK. It isn't really needed for daily usage.

My basic 2 cents worth; I'm sure others will be able to provide much more depth.
 
It is used to reform caps when a unit has been stored or sitting idle for a long period of time. Tubes are high voltage and particularly the electrolitics in the power supply need to be babied back into operation to avoid now or later the dreaded 60 cycle hum.
If you just plug a unit in that hasn't been properly brought up on the variac you stand a good chance of ruining the filter caps in the power supply, or damaging them enough that they will soon fail.
Upon replacing the ruined caps you must, you got it, bring the unit up on a variac.
 
Got it!
Thanks guys.
Guess I will have to invest in a cheap variac since I am not sure the last time it was fired up.
 
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