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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


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    Phase Splitter Tubes and Effect on Sound?

    Disles1
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    Disles1


    Posts : 17
    Join date : 2010-12-21
    Location : Calgary, Alberta
    • Post n°1

    Phase Splitter Tubes and Effect on Sound? Empty Phase Splitter Tubes and Effect on Sound?

    Post by Disles1 Sat Feb 26, 2011 3:52 pm

    To Bob Latino and/or others: On Tubes Asylum I asked a question as to which tubes in the signal path affect sound the most. I'm trying to learn about tubes and was trying to get at: "if you do change to "warm" tubes in the line stage (again an example) do you essentially change the sound that had been "managed" in the phono stage to that new warmer sound; or do you keep some of the previous and just add some features of the latter tubes?" After various answers to my questions I think I understand, much better now, how tubes affect sound.

    In any case, I believe I had understood that the phase splitter tubes in the ST-120 amp don't have a major effect on the sound (or perhaps it's less than the middle voltage tube) so one answer from a poster surprised me. He said: "From my experience with a PP amp, the phase splitter tubes are very very critical to the sound."

    I still have a long way to go in understanding so need more help about whether the 12AT7 phase splitters in the ST-120 are crucial or not?

    Ken

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    Bob Latino
    Bob Latino
    Bob Latino
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    Location : Massachusetts
    • Post n°2

    Phase Splitter Tubes and Effect on Sound? Empty Re: Phase Splitter Tubes and Effect on Sound?

    Post by Bob Latino Sat Feb 26, 2011 5:07 pm

    The two side 12AT7 phase splitter/inverter on the ST-120 (or the VTA ST-70) have less influence on the sound of the amp than the center 12AT7 which is the initial voltage amplifier for both channels. You can try diffrent tubes in the two side positions if you want? I have done so and found little if any difference in the sound when changing out the two side phase splitter tubes.

    In my own ST-120 I use three Mullard CV4024 (12AT7 equivalent) tubes in those three positions. I have pulled the two side tubes and substituted two JAN Phillips 12AT7 tubes for the Mullard's. I can't honestly say that I hear any difference in the sound of the amp although the Mullard's are probably more durable and will last longer in the amp. If I pull the CENTER Mullard out and substitute just about any other 12AT7 tube in there, the sound of the amp changes - not necssarily any "worse" but just a little different. Of the available tubes made today, I have found that the ElectroHarmoninx 12AT7 is a very good tube for the center position.

    Bob
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    Disles1
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    Disles1


    Posts : 17
    Join date : 2010-12-21
    Location : Calgary, Alberta
    • Post n°3

    Phase Splitter Tubes and Effect on Sound? Empty Phase Splitter Tubes and Sound

    Post by Disles1 Sat Feb 26, 2011 11:53 pm

    Hi Bob, could it be that different amp designs use phase splitter tubes to also amplify the voltage - but the ST-120 has a separate driver for that function - and that's why the other fellow experienced an effect on sound?
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    mantha3
    mantha3
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    • Post n°4

    Phase Splitter Tubes and Effect on Sound? Empty Re: Phase Splitter Tubes and Effect on Sound?

    Post by mantha3 Sun Feb 27, 2011 1:46 pm

    I run a Siemens 12AT7/E81CC in my center of my VTA and then I run Mullards in the phase splitter. I was running a nice pair of Raytheon JRP in the phase splitters... Been toying with these vs the mullards. I didn't notice much difference.. I like the Siemens over the mullard in the voltage. The Siemens does the Mullard flash too. I like that flash for some reason.

    I'd like to hear these Shuguang Psvane 12AT7s... I may call Grant Fidelity and see if they will just sell 1.

    http://psvanetube.com/wordpress/wp-content/uploads/wpsc/product_images/12AT7T_600.jpg

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    Bob Latino
    Bob Latino
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    • Post n°5

    Phase Splitter Tubes and Effect on Sound? Empty Re: Phase Splitter Tubes and Effect on Sound?

    Post by Bob Latino Sun Feb 27, 2011 2:35 pm

    Disles1 wrote:Hi Bob, could it be that different amp designs use phase splitter tubes to also amplify the voltage - but the ST-120 has a separate driver for that function - and that's why the other fellow experienced an effect on sound?

    Hi,

    The original Dynaco ST-70 driver circuit had a single 7199 pentode/triode tube per channel. Dynaco came up with a circuit that allowed that single tube to handle BOTH voltage amplification and phase splitting chores. Changing out that single 7199 driver tube would have an effect on the sound of the amp. Dynaco used that circuit because it saved them one tube per each ST-70 amp. Multiply that by the 350,000 or so ST-70's that were made and Dynaco saved a lot of $$$. The Mark II's, Mark III's and Mark IV also have similiar circuits using a single tube pentode/triode driver circuit.

    Modern upgraded replacement driver circuits for the ST-70 like the VTA use three triode tubes on the driver board. Each channel uses "a tube and a half". Triodes are more linear at different drive levels and IMHO do a better job at both voltage amplification and phase splitting than the original Dynaco circuit.

    Bob
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