Isolation transformer recommendations?


I recently added a Scott Marine Radio Model SLR-M to my small collection of vintage receivers (see above).  [The SLR-M is the radio behind the Name that dial! challenge.]  I’ll post more about the SLR-M in the near future–it’s a fascinating WWII era radio with a deep history.

In the meantime, I’m looking for a good, reliable, and affordable isolation transformer for the SLR-M. By design, SLR-M chassis is a part of the overall circuit, thus can be “hot” and never grounded. Several other radios of the era were designed this way and rarely cause electric shock, but since I have small children in the house, I like to play it safe.


At the moment, I’m leaning toward a Tripp Lite IS250 Isolation Transformer. It seems to be a favorite amongst vintage radio collectors, but at $110, it’s certainly an investment I want to make wisely.

If you have advice about isolation transformers, or about the Tripp Lite specifically, please comment below. If you other suggestions, please include links.

Thanks in advance!

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10 thoughts on “Isolation transformer recommendations?

  1. Vathirajan

    Good Blog and thanks for your valuable information about Isolation Transformers. We are also Manufactures and Supplier of Isolation Transformer in Tamil Nadu, India. Keep Blogging. Your Blog is very useful for us.

  2. Mike

    I have used the BK Precision Isopak TR-110 for several years. It has both direct and isolated outputs. What I find particularly useful is its voltage selector. You can set it to 110 volts for your vintage radios. I have a display in my “man-cave” of all the Hally S-38’s and use a TR-110 to power them. Don’t buy one new, look for nice used ones on eBay, that’s how I got both of mine. They are plentiful and cheap and have been in production for decades.

    Mike AC4NS

  3. W4ASZ

    Surplus is great for this application. You might check with Fair Radio Sales in Lima, OH. The Famous Auction Site may have what you need, too.

  4. Michael Black

    The receiver looks hefty enough that something for it would cover most radio needs. You aren’t likely to come across much that needs isolation. There were ac/dc portable tv sets that would draw more power, but unless you repair or collect them, you aren’t likely to deal with them.

    An isolation transformer is simple, just a transformer that puts out the same voltage that is input. Oh sure, worry about breakdown and all that, but any equipment with a transformer faces the same issue, and we don’t worry about how much isolation those offer.

    One way to get isolation in the old days was two back to back transformers with the same voltage rating. Bulkier, but if you find the right transformers cheap, less expensive than an “isolation transformer”.

    I agree with the first poster, if you can drill holes it should be cheaper buying a transformer and putting it in a box.


  5. Dave

    Make sure you get something with a fully isolated secondary.

    Be wary of power tool safety transformers. Their secondaries may be isolated from the the AC line primary, but some are center tapped to ground, so your chassis could be live whatever you do.

    Check with a meter before accepting something.

    As to cost. What price safety for your children?



    1. Thomas Post author

      Very good points, Dave. I would certainly test any transformer I acquire. Very true regarding price as well–I would push my budget for safety.

  6. Robert Gulley

    I will be interested to see what people say – some of the reviews are positive and some negative from Amazon. Seems to be agreement that only the hot is neutralized – negative and ground are together and must be rewired for true isolation?

  7. David Bley

    You pay a lot more for the enclosure, outlets, power cord and switch. I would purchase a 120-120 volt transformer from either Signal Transformer or Toroid Corporation of Maryland If you will only use this to power the one radio, just purchase enough watts to handle that load. If not I would select one that has the best W/$ . Both manufacturers will sell one transformer and I have used parts from both.

    1. Thomas Post author

      I’d like something that I could use with a couple of radios. There are Hallicrafters hot chassis models out there I may pick up in the future. Thanks of the links–I’ll check them out.


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