JTM45 rectifier tube options

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by carryonplease, Feb 9, 2015.

  1. carryonplease

    carryonplease Member

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    Hey all, recently had a JTM45 clone built for me.

    I'm loving the amp although I'm looking to experiment with rectifier tubes as I don't think the amp has enough sag for my tastes. It also gets a little hairy/or harsh when cranked, and from what I've read, getting a bit more sag might smooth it out a little.

    It currently just has a Sovtek 5AR4 in it. I've read conflicting reports on whether these are a real 5AR4/GZ34, so I might end up just trying and old Mullard before I do anything crazy.

    But I have read about rectifiers like a 5V4, or a 5U4. It seems I would need to use 2 5V4s so I don't think that would work but my question is are there any other rectifiers I could try that would mostly plug and play, maybe with just a couple minor bias mods?

    The amp currently uses KT66s, newer chinese ones, and I know I should spring for GECs or something but damn, $300 is a lot of money, I'd rather take care of some cheaper stuff first haha.

    I'm currently running a mixture of NOS preamp glass but I run the amp cranked whenever I use it, so the power tubes should make a bigger difference than usual.

    Edit: the PT is a Heyboer HTS-7119
     
  2. pdf64

    pdf64 Member

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    A Sovtek 5AR4 is likely to have more sag than a Mullard.
    You'll need to check with Heyboer or the maker whether the PT rectifier heater winding can accommodate the 3 amps required by a 5U4.
    However, a 5R4 has similar performance to a 5U4 but only draws 2 amps heater current, same as a 5AR4.

    A more saggy rectifier may not reduce harshness.
    What OT / primary impedance has been used?
     
  3. carryonplease

    carryonplease Member

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    hmm ok, yea I'd have to check. The OT is a nos Drake 103, so it should be 8k.
     
  4. pdf64

    pdf64 Member

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    What screen grid resistor arrangement has been used?
    Each screen grid with its own 1k, or a shared 1k which then splits to 2 x 470 ohm, one for each screen grid?
    I find that the latter gives a smoother, more compressed tone.
     

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