Murex Transtig THF 300 fixes and modifications.

  1. harveyblades Member

    cornwall uk
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    A few mods to a high frequency tig box. When I originally got it the High frequency part was a blob of snot glue with a transistor / transformer / spark plug etc. Not original. Didn't work very well. I replaced it with a unit from china.

    Next up the inductor to smooth DC current. It wasn't doing much either so I took an old welding transformer and filled it with welding cable that I wrapped in fiberglass insulation. Much smoother and starts an arc easier.

    Added some buttons to switch the contactor on and HF off for stick welding and HF / contactor control to the tig switch for tig.

    The thermal cutoff was missing so I put the diodes on a diy heatsink and fan. I haven’t blown it up yet so assume it’s got 100% duty cycle now.

    HF worked well at higher amperage but not low amperage. I don't own an oscilloscope so guessed what was wrong and made the board in the last image. Essentially a bandpass filter. Relay disconnects it once the arc is established. The HF seems to like clean DC and the capacitor allows a small discharge to get the arc going. HF works great now.

    I found another large transformer at the scrap yard and plan to turn it into another inductor and add that soon. My HF assisting circuit may not be necessary then. If I were to do it all again I'd just build a HF box from scratch.
    skotl and Seadog like this.
  2. Nickedemuz New Member

    Nice mods :thumbup:
    I am in the middle of saving a tig ac/DC welder where the hf generator is blown on.
    You mentioned that you could build a hf from scratch. Do you have any drawings/diagrams over how to do that?
    I am thinking about buying one of those cheap Chinese ones but I'm not sure I will be able to nod them to fit my welder. I'm a bit unsure if they are fit to run the whole time which I guess I need when welding ac.