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  • #14302
    CVRS Member

    Hi all, Still in the very early days of setting up my radio shop/room and have spent many hours reading about tube radio and repair, not to mention watching Mr. Carlson’s lab.
    I guess I have been lucky until now, but it has become obvious that I need an Isolation transformer as part of my work bench. I have a Variac, meters and a Stark signal generator, so baby steps.
    The recently arrived Stark came without a cord 🙁 so I have to try and find one. I think it’s a BNC type connector, but I will research it.

    So, to get to the point, I’m looking for a good used Isolation transformer or a cheap means to make my own. Is the one below the best bet?


    Thanks in advance, Gary in Montreal

    John Greenland
    CVRS Member


    A quick and easy way to get an isolation transformer of low to moderate power say 100 watts or less is to use a low voltage transformer,
    lets say out of an older mobile radio supply ( 12 volts at 10 amps ), and connect it backwards.
    You would use your variac to supply the low voltage, say 15 to 18 volts, and connect that to the transformer’s low voltage secondary.
    Adjust the variac to get the 110 – 120 volts on the primary.
    A 10 amp supply of 12 volts will probably get you a 100 to 120 watt isolation transformer.
    That’s enough to run virtually almost any smaller tube radio.
    For example An all american five with miniature tubes requires around 50 watts.
    This assumes your variac can deliver about 9 to 10 amps.

    Just an idea from an old scrounger !

    • This reply was modified 3 years ago by John Greenland. Reason: Too heavy a requirement on the variac
    CVRS Member

    Thanks for the concept John, I can keep my eyes open, but nowadays, swap meets, Sally Ann all out of commission.
    I have been gathering intel on doing alignments so I’ll be more or less ready when the cable comes for the Stark Rf signal Generator. I opened it up and as the ad claimed, it has been “gone through.”
    All the tubes test good and it’s been completely recapped including some added safety caps (I believe). Cleaned all the multitude of rotary contact switches and had a general look around. Has some strange stuff inside (at least to me) Pics below.
    There is a bunch of radios that I’ve done in the past months and they all work O.K., but need to be checked.. I’m guessing my Hallicrafters S 38 would be bad first candidate as the manual says “Alignment should not be attempted by inexperienced persons as maximum performance is obtained only by intelligent alignment”

    O.K., I’m sufficiently intimidated, so I guess i’ll cut my teeth on an AA5 😉

    Gary in Montreal

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