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Isolated variac suggestions - bridkarl - 08-17-2025

I’ve been using this cheap non-isolated variac feeding into a fused isolation transformer. 

Not had any issues, - I’m sort of obessive about one hand in my pocket don’t touch anythinh but I’d like to upgrade to a nicer setup.
I’m thinking about a Sencore PR-57

RE: Isolated variac suggestions - morzh - 08-17-2025

I suggest a separate isolation transformer.

This is what I have. The Variac is plugged into it.


If you buy an isolated variac, it will likely have an undersized isolation transformer inside, so your power output will be limited. While enough for some radios, it might not be for the large ones.

RE: Isolated variac suggestions - bridkarl - 08-17-2025

Sounds like I have it set up properly then as I have it. I have the variac plugged into the gcfi fused line than plugged into the iso transformer which is also fused. 

I usually also have a clamp on ammeter in this so it seems sufficient for smaller table radios like this 42-327 I picked up today.
I also have this huge triad n66a iso transformer.
Currently downsizing for retirement so lots of stuff like that is packed away but I’ll keep this in mind when I set up my new shop. Thanks

RE: Isolated variac suggestions - morzh - 08-18-2025

GFCI might not work with isolation transformer.

RE: Isolated variac suggestions - TV MAN - 08-21-2025

I have my isolation trans before my variac. Oh, and if you saw my variac, you probably wouldn't approach my bench at all! Icon_lol

RE: Isolated variac suggestions - bridkarl - 08-21-2025

I just have a large industrial power strip that I plug the iso transformer into.No issues except once in a while a receiver will trip the breaker. Usually no issues. My bench is a home built out of wood.

RE: Isolated variac suggestions - bridkarl - 09-18-2025

Picked up a Sencore PR-57 isolation transformer/variac today for $100.

If it works great - nicer than my current jury rigged variac/ammeter/voltmeter. Just using one of those cheap $109 chinese variacs off ebay and a home made iso transformer with a plug in voltmeter. 


If not I can throw it on ebay - someone will pay $75 just for the parts like the button assembly and meter.

RE: Isolated variac suggestions - radiorich - 09-18-2025

Hello bridkarl ,
What great find I have owned PR-57 since it first came out and it had been using in my repairshop on daily basis since new !

Sincerely Richard

RE: Isolated variac suggestions - bridkarl - 09-19-2025

This was a storage locker find so the ebay seller had no idea what it was and just wanted it gone. Need to check the calibration, but a great addition to my shop.
Now I just need a modern oscilloscope and I’ll be all set up. I have the rest of what I need for these like a signal generator, a frequency counter, and a new multimeter.

RE: Isolated variac suggestions - radiorich - 09-19-2025

Hello bridkarl ,
What great deal and I know what you mean about modern scope I have older Analog scopes and thought about buying a never digital scope.
I do a lot of solid-state repairs, So I have used since the 80s a Weller Soldering Station I am on my second one now.

My two main handheld meters are Flukes a 77 and 87 but when my shop was going full steam 6 days a week I had bench fluke meter too. another item you might want later is a good variable dc power supply Also capacitor and inductor tester.

Sincerely Richard

RE: Isolated variac suggestions - bridkarl - 09-19-2025

I think I can get a new 50MHZ 4 channel scope like a Rigol for $350'
I basically do AM table radios -- philcos 1935-1950 mostly. Plus some repair of tube type ham radios. I also have a 1940s tv set in there somewhere.
I generally just replace caps so a tester seems sort of extra but ok.
For my purposes which is just fixing junk I find online as a hobby.I probaly am getting good enough I could do repairs well enough to flip these old radios on ebay if I wanted. Just haven't been able to make that work financially on paper yet.

RE: Isolated variac suggestions - radiorich - 09-19-2025

Hello bridkarl ,
the one thing I would get first is a good Meter and far as other tools a good soldering iron and set of diffrent plyers and you will want to get some alighment tools plus you might post to ask the group what common value parts to keep on hand .

Sincerely Richard
P.S. signal generator for alignment .

RE: Isolated variac suggestions - MrFixr55 - 09-19-2025

I don't have any isolation transformer or Variac. (Actually, I have an isolation transformer but I don't use it) I guess I live on the wild side. My hair is curly because I have been electrocuted more times than Kirk (Old Restorer). What I DO do is to correct the "Switch in the Neutral" syndrome that hot and warm chassis sets suffer from.

An isolation transformer should not trip a GFCI if all the filters are on the secondary of the transformer. (I believe that the GFCI does not measure the amount of current on the ground, it measures the difference between "Line" current and "Neutral" current. In fact, on some of our installations with multiple computers in the same power line, we were required to install an isolation transformer to comply with IEC60601 leakage specs due to the multiple Hopkins filters in the same line.

RE: Isolated variac suggestions - bridkarl - 09-19-2025

I have all the various hand tools I need plus dremels, chassis punch, riviting tools.alignment tools. Plus the scopes, meters, etc.

I'm planning to retire so my only requirement in my new house is basement shop of 10 to 20 square feet that I can get all my tools organized and my supplies.

I get it all done but I'd like it to be better organized,

462ron - 462ron - 09-20-2025

Bridkarl it sounds like you’re getting your shop setup in fine order. I am NOT digital savvy in anyway, old school here, and while there are some good features on these scopes I fear it would overload my old brain and make it difficult to to use. I do have a more modern, if you can consider 70s era modern  Icon_lolno solid state oscope dual trace 15 MHZ that works for me so far. As for a meter, I have a B&K 277 FET-VOM, a solid state version of a VTVM, it is super sensitive with a 15 Meg input resistance. As for an isolation transformer and variac, what I’ve been using for years is an RCA Isotap II that can be found sometime on eBay. It’s one unit that is an isolation transformer that the output can be varied in 5V steps from 25V to 150V all in one and I believe it’s good for 400 Watts.
@MrFixr as far as Kirk being electrocuted, he’s still kicking as I saw him yesterday at Kutztown!

Ron