5U4- safe switch from a GZ34 in a '90s AC30 RI?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Exocaster, Mar 2, 2012.

  1. Exocaster

    Exocaster Member

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    I recently acquired an older Sylvania 5U4 rectifier tube. I'm curious about giving it a spin in my AC30- '90s Korg-era RI, 6 input NMV with Blues. I'm aware of the voltage sag and decreased output I'd get from replacing the GZ34 with the 5U4. I don't know, specifically, if the PT in that era AC30 is up for the task though due to the greater heater current draw from the 5U4.

    Anyone?
     
  2. Blue Strat

    Blue Strat Member

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    Instead of wondering (because I don't know if ANYONE has the answer), use a 5R4 rectifier instead. They're cheap, have the same 2Amp filament draw, and have about the same effect.

    A lot of AC30 customers have done this with great success.
     
  3. LowellH

    LowellH Member

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    On that amp it will, without a doubt, burn up the 5V winding. Might take a couple years though. I have seen it happen twice. Go with Mike's suggestion
     
  4. Blue Strat

    Blue Strat Member

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    Good to know!
     
  5. Exocaster

    Exocaster Member

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    Duly noted! Seeing as that's my main gigging amp, that would be bad times. :drown
     
  6. pdf64

    pdf64 Member

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    Be advised that 5R4 can be a big bottle type tube and doesn't fit into some AC30 cab / chassis designs, eg my 60s JMI. The Korg design may be fine, especially if it's a single section chassis with the tubes orientated horizontally.
    Pete.
     
  7. Blue Strat

    Blue Strat Member

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    Some are, and some are the same size as 5U4GBs (which are still taller than 5AR4s).

    Anything with a "B" in the suffix is the size of a 5U4GB.
     
  8. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Good information to know! I thought the 5R4 would drop the B+ too much.

    Personally, I use a 5V4(G), as it is more like the GZ34 (slow warmup indirect heater; 2A current draw). 5R4G would probably be too large a bottle; my smaller 5V4G barely fits in AC30CC, with the heat shield removed.

    - Thom
     
  9. Blue Strat

    Blue Strat Member

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    "Too much", as anything, is subjective. In my experience, 5V4s barely drop the B+ at all but that's been in 2-6V6 amps which don't draw as much idle current as 4 -EL84s. It's all relative to the amp's total idle current and how loud you're playing. More drop at higher idle and idle volumes.
     
  10. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Good point. Enjoy your Deluxe!

    - T
     

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