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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


2 posters

    Dual rectifiers on a ST-120?

    kevinmi
    kevinmi
    kevinmi


    Posts : 88
    Join date : 2009-11-17
    • Post n°1

    Dual rectifiers on a ST-120? Empty Dual rectifiers on a ST-120?

    Post by kevinmi Sat Dec 22, 2012 1:48 pm

    Is it possible to install another rectifier tube in a St-120 amp, and would there be any benefits in doing so? I've seen other tube amps with dual rectifiers, and I was just curious. I'm going to be upgrading my ST-120 amp over the Holidays, so I thought it would be good time to ask if this modification was feasible. If so , does anybody have have the schematics for wiring the amp for dual rectifiers?
    I've run both tube rectifiers and Weber SS rectifiers, and I prefer the sound of a tube rectifier. Maybe it's all in my head, but it sounds more lifelike to me.
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    Bob Latino
    Bob Latino
    Bob Latino
    Admin


    Posts : 3263
    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°2

    Dual rectifiers on a ST-120? Empty Re: Dual rectifiers on a ST-120?

    Post by Bob Latino Sat Dec 22, 2012 4:35 pm

    Hi Kevin,

    The only way to do what you suggest (use two GZ34 tube rectifiers) is to remove the quad cap and somehow rig up another tube socket for a second GZ34 in the quad cap cutout. You would then place the quad cap somewhere inside the amp.

    Yes - The VTA ST-120 runs a GZ34 tube right at it's limits (250 milliamp current flow). If you have inefficient speakers and/or hard to drive speakers and/or play your amp at high volume levels a good percentage of the time, then I would recommend the Weber WZ68 solid state rectifier. The Weber WZ68 can flow double the current of a single GZ34 tube rectifier or to think of it another way > A single Weber WZ68 can flow as much current as TWO GZ34 TUBE rectifiers.

    Your mention of the tube rectifier "sounds more lifelike to me" is maybe the effect of the tube rectifier "sagging" the B+ voltage at high current demands. Many guitar tube amp users like the type of sound they get out of their guitar because of the slight voltage sag of a tube rectifier during high current demand.

    Consider also that virtually all the USA manufacturers of tube amps today use SOLID STATE rectifiers. McIntosh, Conrad Johnson, Balanced Audio Technology, Rogue etc. all use solid state rectifiers in their tube amps. Dynaco themselves used solid state rectifiers in the SCA-35 and the ST-35 amps.

    Bob
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    kevinmi
    kevinmi
    kevinmi


    Posts : 88
    Join date : 2009-11-17
    • Post n°3

    Dual rectifiers on a ST-120? Empty Re: Dual rectifiers on a ST-120?

    Post by kevinmi Sat Dec 22, 2012 5:06 pm

    Bob, Thanks for the reply. I actually don't listen at high volumes, and my Khorns are quite efficient. I have a Weber WZ68 rectifier that I had used for over a year, but when I purchased Mullard GZ34 tube and replaced the Weber, I thought it sounded better. Maybe it's just in my head. Besides, I live in Michigan, and can use all the tube generated heat I can get! I'll do a comarison between the Weber and the GZ34 after I get the new driver board built and installed next week.
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