Variac or not?

[jeyurkon]

Originally Posted by Chimes

I guess I don't see your concern. You say you have already recapped the set, so the next step would be to bring it slowly on the variac and watch for anything unusual. If it comes up and no smoke or fireworks, then time to trouble shoot any problems there may be.

I have never bothered to reform any new electrolytic capacitors and never had a problem and I have replaced hundreds. I hear the audio folks talk about that as they seem to think capacitors need to be "broken in", but with modern electrolytics that is simply not necessary.

I'm not perfect. I could have put one in reversed. The schematics don't show the correct polarity for all of the electrolytics which adds to the confusion. If I bring it up slowly I might catch such a mistake before serious damage occurs.

Or, I could have a solder splash that I missed.

The errors in the schematic don't surprise me. While repairing my Sony STR-V55 receiver I discovered four electrolytics that were not only shown backwards on the schematic, they were installed that way at the factory. Fortunately these only see 10mv since they bypass the emitter resistors.

John

[Chimes]

Originally Posted by Big Dave

As far as reforming goes, I am now using the method the manufacturers used. Refer to Amptech Systems (John Horvath) website. He explains it in detail. Back to variac or not, I definitely use a variac before and after recappig. This applies to either replacing every lytic in sight or reforming existing ones.

I took a look at your web site and on the restoration tip page under "do you want to plug it in" you state, "1. DO YOU WANT AN ELECTROLYTIC CAP TO EXPLODE AND SPREAD PCB'S ALL OVER YOUR PLACE?"

I wasn't aware that electrolytic caps contained PBCs, some oil filled caps, yes. I don't think the standard electrolytic one would find in an old tv or radio would contain any PBCs. Correct me if I am wrong.

[andy]

...

[nasadowsk]

Only oil filled ones had PCBs to any noteable extent, and even there, it's not much.

Big deal, wipe it p and toss the mess away, and you're good to go. The PCB danger's overstated bigtime they were used in everything years ago...

[Chimes]

Originally Posted by andy

I like to use a variac, but not to reform caps. Bringing it up gradually over many minutes is useless at best, and at worst can cause other problems. When I bring a set up, I do it over about 30 seconds. The idea is that if there's a serious short, I'll notice the problem before any more damage is done.

Exactly.

[old_tv_nut]

I don't think it's necessary to do a slow forming of NEW 'lytics. When I worked on new circuits in the lab, we just turned them on when the tech finished constructing them. However, in an old set even with new 'lytics, I do feel safer starting, say, 10% low rather than 10% high! Hand on switch while watching for arcs or smoke the first time!

[peverett]

I use a variac to bring up re-capped items for the first time. This, as mentioned above, helps isolate inadvertant shorts, etc.

Luckily, the variacs that I have are coupled with an isolation transformer and have both current and voltage meters. This makes it safer to bring up hot chassis sets and makes it easier to spot trouble.

These particular variac systems are identical Heathkits. I built one myself years ago and purchased the other already assembled.

[jeyurkon]

Originally Posted by peverett

I use a variac to bring up re-capped items for the first time. This, as mentioned above, helps isolate inadvertant shorts, etc.

Luckily, the variacs that I have are coupled with an isolation transformer and have both current and voltage meters. This makes it safer to bring up hot chassis sets and makes it easier to spot trouble.

These particular variac systems are identical Heathkits. I built one myself years ago and purchased the other already assembled.

I have an isolation transformer and I just purchased a new variac. I was curious to see if a watt-miser would work at reduced voltage. It didn't. I saw a brief flicker in the display, I guess it needs to come up cleanly.

I kept increasing the variac to 120VAC when the lights went out. The watt-miser has surge protection built in. 120 on the dial of this new variac turns out to be 140VAC at the output. It has a built in voltmeter and when it reads 120VAC the output is actually 130VAC.

The surge protector just did it's job and tripped a circuit breaker. The watt-miser is o.k. I was hoping to monitor power with it as I brought things up. Guess I'll go back to the trusty ammeter.

John