variac for power source

[moons]

Hello Again
Is going to destroy Vintage Altec Mixers and Preamps or I guess any vintage gear if a Variac is not used to power them up,Will it degrade the transistors and capacitors within the unit by plugging it in directly to 120v and flipping the unit on.
Thanks Again

[moons]

Ok so once the unit has been working sucessfully for a while then it should be ok to power on straight from the wall plug?
In your opinion what length of storage time would generally warrant concern to use a variac.
At any rate thanks for your reply on this it may save some of us some un pleasent suprise the next time we flip the switch on some cherished old gear.

[bfish]

Correct.

There's really no predictable time period. It depends on the quality of the caps originally, the overall rate of use, storage temps, and other factors. As a general rule of thumb, I'd say that anything that's 20 yrs old or older, and has been unused for the last 4-5 yrs should be initially powered up slowly with a variac.

Electrolytic failure isn't necessarily destructive, at least in its' early stages. Small areas of deteriorated dielectric in a cap can allow leakage, which is often evidenced by hum or turn-on "pops".

Electrolytic type caps are the only components that cause this problem, as their remaining stable depends on them being regularly powered, since the dielectric is formed between the dissimilar electrodes by electrically-induced oxidation. Film caps and other types using a permanent dielectric layer may drift in value over time, but seldom cause destructive shorting.

For replacements, use only NEW electrolytics, unless you're well-versed in reforming NOS caps, and have the equipment to do so. New HV electrolytics for old tube gear can get expensive, but are cheap compared to xfmrs.

When you consider that electrolytics made in the '50s and '60s had an expected service life of 4-7 years, ....

You're welcome.

[bfish]

It certainly can.

The biggest variable is the length of time since the unit was last used regularly. If it hasn't been used in years, or if you don't know the use history, there's a fair chance it'll smoke.

The culprits are the electrolytic caps. Without regular use, the dielectric layer deteriorates, eventually creating a short that will destroy other components in the circuit. "Bringing it up slow" with a variac gives them a chance to re-form the dielectric under low voltage conditions.

Variacs are cheap enough on eBay that anyone buying old gear should have one. Then again, if the stuff you buy was "powered up to test" by the seller, it may be too late.

In a pinch, you can wire a 50W incandescant bulb in series with the unit's power cord and turn it on. As the electrolytics reform, the bulb will glow a little brighter, with the series voltage drop it provides giving a little protection. When the bulb glows normally, usually in less than an hour, it can be removed from the circuit.

After you've smoked a few pieces of expensive gear, you'll begin doing blind replacement of all electrolytic caps before you plug it in. That's assuming you care about it providing longterm reliable service more than "looking 100% original".