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Combination Isolation Transformer, Bulb Limiter with Bulb Bypass

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  • Combination Isolation Transformer, Bulb Limiter with Bulb Bypass

    MEF members….

    MEF has several posts on Isolation Transformers and Bulb Limiters. I wasn’t sure which would be the best post for this follow up. But since it is a combo device, I decided to open a new thread. If you want more info on either device, please look for those threads.

    I wanted to share something I built, based on prototypes from Terry Dayton’s (How to Modify Re-Purpose Heathkit IP-12 DC Power supply into a bench AC Variac, D-Lab Electronics) and Ron’s Vintage Electronics “AC Variac and Dim Bulb all in one Episode 1 and Episode 2.

    DISCLAIMER – Like many of you, I am a hobbyist. So use extreme caution when working with these types of devices. Please view the Todd Fun video on Isolation Transformer modifications. There are other YouTube videos on the same subject (Uncle Doug, Mr. Carlson’s Lab, and a few others). BE CAREFULL !!!

    The end result of my project is a single box that contains an (1) Isolation Transformer and (2) a Bulb Limiter with a bypass switch. Since I already have a Variac, I left that unit as a stand-alone and this is where I connect the Iso/Limiter unit. I had an Iso Transformer that I salvaged from a non-working Viz unit. The variac part was bad, meters not working, etc. But the Iso Transformer was ok. You can read my notes in the Schematic Diagram I posted.

    Having the analog Voltage and Ammeters is very helpful. The meters are not exact, but they do give you helpful information for the device output. Adding the bulb bypass switch is also helpful. That way, I do not need to keep disconnecting and reconnecting the Device Under Test to and from the Bulb Limiter.

    Sorry for the messy schematic, but I think you get the idea!!

    Click image for larger version

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    Click image for larger version

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  • #2
    That Heathkit reminds me of the IM-5284 analog multimeter I built in tech school. I still have it!
    "Yeah, well, you know, that's just, like, your opinion, man."


    • #3
      I should add, I removed the original faceplate from the Heathkit and replaced it with a plastic one, something I could easily drill and cut into.