SFDR: Do 6L6's NEED a SS recto...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by 55hz, Apr 12, 2008.

  1. 55hz

    55hz Member

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    or can I use a GZ34/5AR4? Thats what I'd like to do.... Maybe some JJ 6V6's with a GZ34/5AR4? and a completely off the wall question... I've got a '75 SFDR "export only" model with the selectable tranny. Its got waxed cloth wiring as opposed to the normal "plastic" covered. Did Fender have a stockpile of these? could that tranny be older? does anyone know if the export models have anything else different/strange about them? Couldnt really find anything, anywhere about them... Thanx
     
  2. phsyconoodler

    phsyconoodler Member

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    You can use a 5U4,5AR4 or diode rectifier.However,you need to check the bias with each rectifier so you don't exceed the tubes rating.
     
  3. Buckshot

    Buckshot Member

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    In a Deluxe Reverb, the purpose of the SS rectifier w/ 6L6s are for the survival of the power transformer, not the tubes themselves. You can run a 5AR4, but it might be expensive & destructive in the long run. If it were me & i HAD to have the sag & HAD to run 6L6s, I'd buy a Weber Copper Cap to save stressing the PT - it'll give you the sag without demanding the filament voltage from the PT that an actual tube will.
     
  4. 55hz

    55hz Member

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    how bout 6V6's with a 5AR4? More headroom with tube recto(thats not a 5u4)... is it possible?
     
  5. Buckshot

    Buckshot Member

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    Yup! no problemo;)
     
  6. Blue Strat

    Blue Strat Member

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    Woah big boy! You're telling him that it's unconditionally ok to increase the plate voltage (by using a 5AR4) which may exceed the specs for the 6V6s and the power supply capacitors.

    The REAL answer is....."maybe". Definitely don't use a 5AR4 with stock capacitors. It would be ok if you have 500V capacitors.

    If the resulting plate voltage exceeds 450V it could spell danger for your 6V6s.

    DEFINITELY rebias if you attempt this.
     
  7. Buckshot

    Buckshot Member

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    My understanding was that the same spec transformers & caps were used in the SFDR as the BFDR (which came stock from the factory with the 5AR4). I certainly defer to & agree with Mike if that understanding was incorrect. And yes, a rebias is necessary any time you change rectifiers - Idid not infer or intend to infer otherwise.
     
  8. Blue Strat

    Blue Strat Member

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    The PT's DID change which is why the resulting B+ is approximately the same in BF's with a 5AR4 and SF's with a 5U4.
     
  9. 55hz

    55hz Member

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    Bluestrat, thanks for the help! are the caps your talking about the ones in the "can"? and the value would need to be: 16mfd/500v?
     
  10. Blue Strat

    Blue Strat Member

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    Yes, those are the ones.

    When doing a cap job be sure to replace the bias supply cap(s) on the small board inside the chassis. When these fail they will take out your power tubes and possibly even you output transformer.
     

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