MC2105 & c28 sat 5yrs: Variac or no?

I have an MC2105 and a C28 (+MQ101) that the previous owner says worked fine last they were used, but it's been 4 or 5 years since. I have a variac, and use it on old tube gear, but I've also read discussions about some of the newer solid state gear NOT surviving low voltages due to PS design, etc.

So, is a slow rise on a variac a good idea?
A "soft start" (30 seconds to 120v) the thing to do?
Or should I just plug 'em in and turn 'em on?

?
Joe

Goldenvoice said:

So, is a slow rise on a variac a good idea?
A "soft start" (30 seconds to 120v) the thing to do?
Or should I just plug 'em in and turn 'em on?

Click to expand...

Since you have the Variac, it can't hurt to 'bring it up slow' the first time.
The Mcintosh has those nice, big oil filled GE power supply caps, and they aren't likely to do anything unexpectedly spectacular after being idle for a few years. I'd check them for any signs of leakage underneath.

Can you monitor current draw as you bring the voltage up? If not I would use a simple dim bulb tester to monitor initial current draw.

A dim bulb will protect you if anything fails, but it's not very helpful in bringing up caps slowly. There are very few amps that have a problem with being brought up slowly on a Variac, typically those with switching supplies. If it were a huge issue they wouldn't survive brown-outs and weird low voltage line situations. Oil filled caps (AFAIK) don't "form", so it shouldn't matter how fast you go. Electrolytics won't degrade much in 5 years, but I'd bring it to maybe 30 VAC for 15 seconds, 60 VAC for 30 seconds, then run it at about 100 VAC for 5-10 minutes. Monitor for any overheating, smoke, etc. I go slower and in more steps for tube equipment and older stuff, but that should be sufficient for 5 years of disuse, assuming nothing else is wrong. FWIW, "owner says it worked fine" has rarely worked out for me.

OK, I removed the bottom plate and the cage, and dusted her out, cleaned the chrome chassis, reassembled, and did a soft start on the variac. All good - sound great!

I had a CD source running in at the time, and was amazed she came on and ran somewhere between 10 and 20 volts.

Thanks for the advice :thmbsp: