Using a 5y3 in a gz34 slot???

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by 69strat, Mar 10, 2006.


  1. 69strat

    69strat Member

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    I have an old tungsol 5y3. I was thinking of swopping out my gz34 in my jtm 45. Can I do this? What can I expect?
     
  2. brad347

    brad347 Member

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    not sure but I think the 5Y3 draws more heater current than the GZ34?

    Might be able to do it still, not sure... probably depends on the PT but if you do you can expect less clarity, more mud, more sag, more compression. Less headroom.
     
  3. Swarty

    Swarty Member

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    Heater current is not the issue. DC current is the issue. The 5Y3 will only deliver 125mA the GZ34 will deliver 250mA... which is why you only find 5Y3s in smaller amps with smaller tubes like 6V6s.
     
  4. John Phillips

    John Phillips Member

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    You'll blow the 5Y3. The current demand is too great for it - I can't remember the exact figure for a JTM45 but it's in the region of 200mA or maybe a little more.

    If you want a compatible rectifier that will give greater sag, you need a 5R4.

    A GZ37 or 5U4 would not be a good idea either because they do have much greater filament current draw (3A not 2).
     
  5. KLB

    KLB Member

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    John,
    If the circuit draws less than 125ma, that is a pair of 6V6 in a JTM-45, will the 5Y3 be operating safely regardless of what current the PT is capable of putting out? I am assuming a 32mf first filter cap.

    I've been running a 5Y3 in a Germino Club 40 with 6V6. The 5R4 puts about 10 more volts on the plates (410 vs 400v).
     
  6. John Phillips

    John Phillips Member

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    As long as the total current draw at maximum output power is 125mA or less it will be safe, regardless of the PT.

    If the power output is about 20W RMS it will be pretty close though. I would maybe meter it to be sure, if you have the right sort of multimeter and the amp has some way of breaking the current path - the easiest is if it has a HT fuse... clip the meter across the fuseholder (preferably with the amp turned off!) and pull the fuse. Set the meter to read mA and watch what happens when you play loud.

    Or alternatively, assume that if you haven't blown it so far it's probably OK :).
     

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