Variac or not?

[jeyurkon]

I've worried about whether bringing a TV up on a variac is appropriate or not. The concern is the sweep section. If it doesn't start oscillating because of low voltage there are a few bad things that can happen.

I did a little searching and found conflicting answers.

Pharis-video recommends bringing a set up starting at 25VAC and increasing it 5 volts every 5 minutes.

Amptechsystems recommends against using a variac because of the concern that I mentioned.

A variac works great on radios and gives the electrolytics, new or not, a chance to reform. I'm not so sure about televisions.

Has anyone had a bad experience using a variac?

John

[mattdavala]

I usually pull all tubes except for the rectifier and then reform the electrolytics. After that I'll install every section except for the horz. sweep output tube, and check that with the variac.
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Matt Davala

[zenithfan1]

I've thought the same thing John. I do it a little different, I leave all tubes in except for the HOT & oscillator and VOT (oscillator too if not part of the VOT) . When I've left them in, I've heard strange noises and thought it was not so good......

[jeyurkon]

Those sound like good ideas. I'll do that. Guess I'll take out the 6Y6 for the RF HV also.

John

[Big Dave]

Leave the tubes in. I start about 40 volts and raise it by 5 volts every 15 minutes. If a can starts getting warm (not heat transfer from the tubes), I abort. Now, I can reform the lytics. I do disconnect the top cap from the hor out. If the hor out doesn't have a top cap, I tie in the heaters of an equal voltage tube (series string) or remove it.

[jeyurkon]

Originally Posted by Big Dave

Leave the tubes in. I start about 40 volts and raise it by 5 volts every 15 minutes. If a can starts getting warm (not heat transfer from the tubes), I abort. Now, I can reform the lytics. I do disconnect the top cap from the hor out. If the hor out doesn't have a top cap, I tie in the heaters of an equal voltage tube (series string) or remove it.

On the set that I'm concerned with the HOT is a 6BD5GT, so no top cap. The heaters are all parallel so I can just remove the tube.

If I remove the HOT then I want to remove the 6Y6G in the RF HV because I don't want 9.5KV on the CRT if there's no scanning. The rest I would leave in. Well, maybe I'd take out the vertical output, but I think the HOT is the most important one.

Thanks for the info,

John

[Chimes]

You might as well go ahead an replace the electrolytics as you will want to do that eventually anyway. Reforming electrolytics is a crap shoot and I have never had any luck doing so. Even if they appear to reform, they will fail fairly soon. New caps are not expensive and no need to take a chance on old ones.

[radiotvnut]

Originally Posted by Chimes

You might as well go ahead an replace the electrolytics as you will want to do that eventually anyway. Reforming electrolytics is a crap shoot and I have never had any luck doing so. Even if they appear to reform, they will fail fairly soon. New caps are not expensive and no need to take a chance on old ones.

That's always been my way of thinking. I've seen old (and not so old) electrolytics that would work fine one minute and not work (and sometimes blow up) the next minute. Even in failed equipment that's only a few years old, bad electrolytic caps are real high on the culprit list.

[jeyurkon]

The set I was referring to is the Sylvania 1-076 that has a thread started. Even though I've recapped it, I'd like to start it up slowly. A number of the new electrolytics that I purchased needed reforming when I tested them. They'd probably be o.k. with a cold start but I'd rather not stress things.

I did reform every electrolytic that were replacments and those that I decided to keep. The fact that I kept any didn't have anything to do with cost. I had already purchased a complete set of replacement capacitors for the set before I had even taken possession of it.

Even though I tried to be careful, there's also always the possibility that I splashed some solder and made a bridge somewhere. I'd like to find out gradually.

John

[Phil Nelson]

I will chime in with Chimes and say you should replace the electrolytics FIRST, then bring it up on a variac.

You know that you should replace them anyway. Why not do it now?

I have had very poor luck reforming old electrolytics. Even if they seem to function, I would not bet my power transformer on them.

Others may have had different experiences. For me, all it took was burning up one power transformer.

Even if the TV kind-of sort-of works after bringing it up with the original electrolytics, what does that really tell you? You still have a TV full of rotten old caps that need replacement, so you may as well get started.

Just my $0.02,

Phil Nelson

[jeyurkon]

Originally Posted by Phil Nelson

I will chime in with Chimes and say you should replace the electrolytics FIRST, then bring it up on a variac.

You know that you should replace them anyway. Why not do it now?

I have had very poor luck reforming old electrolytics. Even if they seem to function, I would not bet my power transformer on them.

Others may have had different experiences. For me, all it took was burning up one power transformer.

Even if the TV kind-of sort-of works after bringing it up with the original electrolytics, what does that really tell you? You still have a TV full of rotten old caps that need replacement, so you may as well get started.

Just my $0.02,

Phil Nelson

Well, your 2 cents is worth a lot because you have a lot of experience and you've been kind enough to share it with others. I've found a lot of useful information on your web site.

I promise to keep track of any failures of electrolytics that I decided to keep and about how many hours they were in use before failure. I will post each failure on this forum. Hopefully I won't have to embarrass myself too often.

John

[peverett]

I agree with Phil. I tried re-forming electrolytics on a couple of AC/DC radios that I restored. No transformers to fry, but after 6 months the radios were humming again. I now just replace the electrolytics.

[jeyurkon]

I meant for this to be about bringing a TV up on a variac. I believe many do that even if they have totally recapped a set. I'm sorry if it's veered into an electrolytic capacitor aging issue

With the radios I've restored I have completely recapped them. I have a 60's radio that I've done nothing with and it's still playing and a 50's communication receiver that I've also not touched, other than realignments, and it works well. Of course it only has a couple of electrolytics and no paper caps. I've had it before I was a teenager.

I've purchased multi-section axial electrolytics off of ebay with the intention of restuffing them to use in some old radios I have. Although I didn't care if they were good or not the seller claimed they had been tested and reformed. However, he didn't know about testing for ESR. All of the ones that just had paper tubes to seal them had extremely high ESR. The others tested out well. I suspect that any electrolytics that seem to reform and then later fail may have had already marginal ESR.

The ones that I've kept in the set I've tested out thoroughly and are not in sections where they are under much strain.

My temperment is such that I question everything and have a need to check things out for myself. I may be making a big mistake, but I wish to see how long electrolytics, that test better than the brand new and fresh electrolytics that I had intended to replace them with, fair.

John

[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.

[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.