Marsh Deluxe Reverb plate voltage and bias question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by sting7777, Mar 3, 2012.

  1. sting7777

    sting7777 slinger of notes Silver Supporting Member

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    I recently picked up a Marsh DR used.

    I installed new JJ's and using my bias rite set the bias to 25mA at around 470 Volts.

    I know the DR has always run hot and that JJ's can take it but I was still surprised to see a newer clone running the plate voltage that high.

    Anyone else have a similar situation in a newer AB763 clone? Should I even worry at all or just play it?

    thanks!
     
  2. mxvin

    mxvin Member

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    JJs can take that but if you want to run dif 6V6s you may have to mess with it to bring down the PV. What type of rectifier is it running? GZ34 or 5U4GB?
    The 5U4GB will bring the PV down somewhat but does add a slight increase in heater voltage draw. Prob not an issue. But you could check with the Marsh site.
    If you do like JJs then you should be good to go.
     
  3. Blue Strat

    Blue Strat Member

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    A 5R4 will give similar results without the increased heater current draw.
     
  4. mxvin

    mxvin Member

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    cool...good to know. I actually did know that but forgot. Thanks for the refresher....:)
     
  5. sting7777

    sting7777 slinger of notes Silver Supporting Member

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    Thanks for the replies. I have thought about the 5R4 as I am running a GZ34 currently.

    My only hesitation is that I like the GZ34's slow startup that is like having a built-in standby switch.

    Maybe I'll pick up a 5R4 and see what it actually does to the plate voltage and bias point and sound and go from there.

    thanks again!
     
  6. sting7777

    sting7777 slinger of notes Silver Supporting Member

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    Just came across 5V4 - slow startup but lower pV...
     
  7. Blue Strat

    Blue Strat Member

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    Barely lower than a 5AR4 with 6V6s and not nearly as low as a 5U4 or 5R4.

    Doesn't the amp have a standby switch?
     
  8. sting7777

    sting7777 slinger of notes Silver Supporting Member

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    Thanks. I should check out a 5R4 I guess. Any reccomendations?

    Yes it does - but I like the double safety. :)
     
  9. Blue Strat

    Blue Strat Member

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    Kinda overkill if you used the standby switch. ;)

    I've got several 5R4s if you're interested.
     
  10. sting7777

    sting7777 slinger of notes Silver Supporting Member

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    A friend of mine has an RCA 5R4GYB. Any difference in all the suffixes or will this guy work to test out the votlage drop? Thanks for the help!
     
  11. Figaro

    Figaro Supporting Member

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    Just call or email Marsh and ask about it.
     
  12. big mike

    big mike Administrator Staff Member

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    Long as it's 5R4 should be fine.

    Try it. Won't hurt nothin.
     
  13. Blue Strat

    Blue Strat Member

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    What Big Mike said.
     

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