Dead Reverb Driver Transformer

Discussion in 'Glowing Bottle Tube Amp Forum' started by zaraxisof, May 6, 2021.

  1. zaraxisof

    zaraxisof Tele-Meister

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    I was recently given a nice old full tube amp from the 60s. After a common repair procedure it sounds like a charm.
    Only thing left is the reverb circuit.

    Driver transformer is shot, primary windings read dead open. Secondary reads about 4Ω.

    Rvrb tank is partially broken too, missing the one from the four transducer's magnet, so the one spring falls apart from one side. It's a common type 4 tank ohms resistance reading is about 4Ω input and 150Ω output. so i guess smthng 4-8Ω in, 2-5K mΩ out impedance could work as replacement. I have some 4ab3c1b's laying around for splish splash moments. . Could this work?

    Now about Driver Transformer: Tried even unwind it to see if i get lucky and the break is outside. Removed secondary winding, then many hundreds of turns from primary, but no lack. The break is deeper inside the core.

    It uses an ECL86 triode pentode tube to drive the reverb amp, then a driver transformer. After that it uses AC151 germanium for recovering stage.

    Schematic:
    http://b.baldach.free.fr/farfisaFR40/FarfisaFR40_Schematic.jpg


    Found out some other guys used a Hammond 1750AX and worked great. I could also tell my local winder (specializes in tube OT trannies) to wind me a dedicated one for me here. This will cost way lower than Hammond's for sure.
    But, before all those. I have an old unused OT from an old radio laying around. It reads about 4Ω in secondary.
    The radio uses one EL84 for output tube.
    Exactly like ECL86 pentode.

    Can i use this as my driver transformer?
     
    Last edited: May 6, 2021
  2. 2L man

    2L man Tele-Holic

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    I am delighted to hear that custom wound transformer can be cheaper than mass produced :)

    I think you can use that opt to drive low impedance tank.
     
  3. zaraxisof

    zaraxisof Tele-Meister

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    I used that and worked fine. :)
     
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