Variac

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Variac

Post by Oldsmobile Man on Thu Mar 13, 2008 8:38 pm

I'd like to buy myself a variac... Is there anything i should look for?
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Re: Variac

Post by Resistance is Futile on Thu Mar 13, 2008 9:21 pm

One that would handle 250-300 watts and an Isolation transformer for the All American 5 and other hot chassis types
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Re: Variac

Post by LarryC on Thu Mar 13, 2008 9:58 pm

Also some kind of meters both for voltage and current
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Re: Variac

Post by philcoguy on Fri Mar 14, 2008 11:57 pm

Look for one with a fuse it is nice if you have a amp or watt meter. Stay away from any thing that is realy rusty. Only pay more then 30 bucks if the variac is something rare like my 20 amp rca variac! yes I said 20 amp variac!
John Tyminski

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Re: Variac

Post by mikeinkcmo on Tue Mar 25, 2008 9:41 pm

look up MPJA, Marlin P Jones and assoc. They have pretty good prices on variacs, and I'd get at least a 500 watt version. I strongly reccomend you get a Isolation transformer as well, and if you are going to work on test equipment I'd suggest you get a 1kw unit. Neither are cheap but you can find good deals now and then.

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Re: Variac

Post by Where did I put that... on Fri Jun 27, 2008 5:40 pm

This is probably opening a giant can of worms but is one company known for being better than the rest?

Robin
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Re: Variac

Post by mikeinkcmo on Sun Feb 15, 2009 5:23 pm

I agree with the MPJA recomendation for the variac, as that is where I got mine.

On the Isolation transformer front, this company has excelent equipment. Pricey, although I purchased their 1KW unit for $178 including shipping.

http://www.tripplite.com/EN/products/index.cfm?txtEntryID=5&gclid=CPrco-u535gCFQHHGgodIGfYdQ


Last edited by mikeinkcmo on Sat Feb 21, 2009 9:11 am; edited 1 time in total

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Re: Variac

Post by exray on Sun Feb 15, 2009 5:35 pm

Variacs are great. They are even greater when you utilize an inline ammeter. Otherwise you're dependent on detecting smoke at a certain voltage level which is what you hoped to avoid Smile

War story. I used to work on a bench flipping amplifiers which had some well recognized problems. You see that meter quivering and it was a done deal. No waiting for the xfmr to let out the magic smoke at a certain voltage.

Gotta have an ammeter with the variac. They are inseparable.
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Re: Variac

Post by Badrestorer on Sun Feb 15, 2009 8:38 pm

Exray is right. Using a variac without an ammeter makes no sense. You have to keep a constant eye on a radio's current draw, especially when powering it up for the first time.
Here's the setup I put together to help me do that. Used a couple of cheap Hobby Lobby boxes and picked up a voltmeter and ammeter on ebay. Later on the larger 302B replaced the smaller ammeter as it had multiple scales.

[img][/img]

Regards,
John

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Re: Variac

Post by Lou deGonzague on Sun Feb 15, 2009 10:07 pm

The RCA VIZ line made a combination variable voltage and isolation transformer model WP-27A Isotap II. It's a 400 watt unit that goes from 25 to 150v in 5v increments. As stated you must have some kind of meter to monitor current to make all this meaningful. A 0-2 amp meter in a box with a fuse and pilot light is just right for old radios. I have a nice Simpson 0-150 watt panel meter with a fuse and panel lamp with a socket and line cord that gets used with any radio I work on.

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Re: Variac

Post by beebs on Sat Feb 21, 2009 1:20 am

Wow...there's more to this variac thing that I thought. I've just got the little Rat Shack model from the 60s/70s that has a dial and a plug, and I've used it on my Dynacos. When I've powered up my old Dynaco equipment for the first time, I've generally just started at 5 volts or so, and left it for an hour. Then every hour over the next eight to ten hours I bump it up about ten or so volts until I get it up to 110V. Things have been fine so far doing it that way, so I'm reading all this with interest...already learning good stuff!

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Re: Variac

Post by mikhail7 on Wed Sep 01, 2010 11:00 am

philcoguy wrote: ...Only pay more then 30 bucks if the variac is something rare like my 20 amp rca variac! yes I said 20 amp variac!
John Tyminski

I have a Superior brand 20 amp variac but I'm so technically challanged I'm not sure how to connect it. It's not rusty but it does have a minor dent. This sucker is heavy and I bought it at a hamfest in Lowell MI two years ago. I think I paid $15 for it, something like that.

Mike

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Re: Variac

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