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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


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    ST120 Driver Tubes: Should they all be the same?

    ChetJettison
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    ChetJettison


    Posts : 35
    Join date : 2021-12-03
    • Post n°1

    ST120 Driver Tubes: Should they all be the same? Empty ST120 Driver Tubes: Should they all be the same?

    Post by ChetJettison Fri Dec 03, 2021 6:05 pm

    I built a VTA ST120 from a Bob Latino kit. I enjoy it very much! But I've lately been wondering about the three small driver tubes. I have a whole slew of questions about them, which I will ask here.
    What exactly do those do? Right now I'm just using the tubes that came with the amp, but the center tube is a different brand from the outer two tubes. Shouldn't they all be the same? Perhaps a factory matched trio? Or at least all the same make from the same manufacturer?
    Is there any effect to tube rolling these? Is there an "ideal" tube for this application? I'm using quad-matched Tung-Sol 6550 tubes and a vintage Amperex GZ34 rectifier tube... are there driver tubes that would be well suited to the Tung-Sol 6550s?
    Basically I'm hoping somebody here (who knows more than I do, which is close to nothing!) can give me the skinny on driver tubes.

    My best to all!
    - Chet
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    Bob Latino
    Bob Latino
    Bob Latino
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    • Post n°2

    ST120 Driver Tubes: Should they all be the same? Empty Re: ST120 Driver Tubes: Should they all be the same?

    Post by Bob Latino Fri Dec 03, 2021 8:43 pm

    ChetJettison wrote:I built a VTA ST120 from a Bob Latino kit. I enjoy it very much! But I've lately been wondering about the three small driver tubes. I have a whole slew of questions about them, which I will ask here.
    What exactly do those do? Right now I'm just using the tubes that came with the amp, but the center tube is a different brand from the outer two tubes. Shouldn't they all be the same? Perhaps a factory matched trio? Or at least all the same make from the same manufacturer?
    Is there any effect to tube rolling these? Is there an "ideal" tube for this application? I'm using quad-matched Tung-Sol 6550 tubes and a vintage Amperex GZ34 rectifier tube... are there driver tubes that would be well suited to the Tung-Sol 6550s?
    Basically I'm hoping somebody here (who knows more than I do, which is close to nothing!) can give me the skinny on driver tubes.

    My best to all!
    - Chet

    Hi Chet,

    The two outside (phase splitter/inverter) driver tubes should be the same but the CENTER tube may be different than the two outside driver tubes. In all the newer VTA amps since April of 2012, you can use a 12AU7 or the military/industrial versions of the 12AU7 < the 5963, 5814, 6189 or the Mullard (Valve Electronic) CV4003. You can also use a 12BH7 which is close enough to a 12AU7 to work OK, Do NOT use any other 12**7 tube in any of the VTA amps ! (like a 12AX7, 12AT7, 12AY7 etc.) The use of the last three tubes mentioned can damage components on the driver board.

    Bob
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    ChetJettison
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    ChetJettison


    Posts : 35
    Join date : 2021-12-03
    • Post n°3

    ST120 Driver Tubes: Should they all be the same? Empty Re: ST120 Driver Tubes: Should they all be the same?

    Post by ChetJettison Fri Dec 03, 2021 8:51 pm

    Thanks for the reply, Bob! Given the information you have just supplied, I have some follow-up questions.
    -What does the center tube do?
    -Is there any benefit to the three driver tubes being identical? Say, a matched trio of 12AU7s
    -Is there any consensus on which tube brands are best for the job?
    -Currently my amp is running a raytheon in the center, and clear-top RCAs on the outsides. Are there upgrades to be had?
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    Bob Latino
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    • Post n°4

    ST120 Driver Tubes: Should they all be the same? Empty Re: ST120 Driver Tubes: Should they all be the same?

    Post by Bob Latino Fri Dec 03, 2021 9:03 pm

    ChetJettison wrote:Thanks for the reply, Bob! Given the information you have just supplied, I have some follow-up questions.
    -What does the center tube do?
    -Is there any benefit to the three driver tubes being identical? Say, a matched trio of 12AU7s
    -Is there any consensus on which tube brands are best for the job?
    -Currently my amp is running a raytheon in the center, and clear-top RCAs on the outsides. Are there upgrades to be had?

    You only need to change out the CENTER driver tube to slightly alter the sound of the amp. As long as the two outer driver tubes are working as they should, changing them out won't really affect the sound of the amp much. The best value for the center tube would be a USA made (RCA, GE or Sylvania) 5963, 5814 or 6189. You can still get these three tubes (made by RCA, GE or Sylvania) at reasonable prices on Ebay. The 5963's tend to be a little less costly than the 5814 or 6189 tubes but they are every bit as good as the 5814 and 6189. The 5963 is less costly only because the supply is greater than the other two tubes mentioned.

    Bob
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    DavidR
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    • Post n°5

    ST120 Driver Tubes: Should they all be the same? Empty Re: ST120 Driver Tubes: Should they all be the same?

    Post by DavidR Tue Dec 07, 2021 10:26 am

    I have some nice tubes for sale. They are listed in the FOR SALE thread.
    The Mullard CV4003 or the Tung Sol 12BH7A tubes would be a nice upgrade in the center position.

    MechEngVic likes this post

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