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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

    ST-120 choke substitution

    baddog1946
    baddog1946
    baddog1946


    Posts : 319
    Join date : 2010-02-03
    Location : Costa Rica
    • Post n°1

    ST-120 choke substitution Empty ST-120 choke substitution

    Post by baddog1946 Mon Jan 16, 2012 10:07 am

    Hi Bob:
    I have a couple of questions about alternative chokes for an ST-120. I notice you now use the C-24X chokes by "Triad" for the ST-120.
    These C-24X chokes flow 240mv. which is more than the c-354 and have similar dimensions to a c-354.
    My question is this;
    if there was enough space to put a slightly larger choke in there would the Triad C-36X or the C-17X be suitable or desirable for use in the ST-120? Would the use of either of these be an advantage since they flow about 300mv.?
    I am building an ST-120 in a slightly bigger chassis and have the room for larger chokes.
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    Bob Latino
    Bob Latino
    Bob Latino
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    Location : Massachusetts
    • Post n°2

    ST-120 choke substitution Empty Re: ST-120 choke substitution

    Post by Bob Latino Mon Jan 16, 2012 12:38 pm

    baddog1946 wrote:Hi Bob:
    I have a couple of questions about alternative chokes for an ST-120. I notice you now use the C-24X chokes by "Triad" for the ST-120.
    These C-24X chokes flow 240mv. which is more than the c-354 and have similar dimensions to a c-354.
    My question is this;
    if there was enough space to put a slightly larger choke in there would the Triad C-36X or the C-17X be suitable or desirable for use in the ST-120? Would the use of either of these be an advantage since they flow about 300mv.?
    I am building an ST-120 in a slightly bigger chassis and have the room for larger chokes.

    Hi George,

    The C-17X is a good choice if you have a custom chassis with a chassis depth of 2 3/8 inches or deeper. The C-17X won't fit into into a standard ST-70/ST-120 type chassis because you only have 1 3/4 inches of INTERNAL depth in a stock chassis. This is why the C-17X is not used on the VTA ST-70/ST-120 amps. It is too "tall".

    The Triad C-36X choke is physically smaller (2 inches mounting centers vs. 2 3/8 on the C-24X) and has less inductance than the C-24X. It does have slightly more current handling than the C-24X. Although I have never tried a C-36X choke in an ST-70/ST-120, my feeling is that it would probably run hot do to it's smaller physical size and consequently less "iron" to act as a heat sink.

    Bob
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    baddog1946
    baddog1946
    baddog1946


    Posts : 319
    Join date : 2010-02-03
    Location : Costa Rica
    • Post n°3

    ST-120 choke substitution Empty Re: ST-120 choke substitution

    Post by baddog1946 Tue Jan 17, 2012 10:36 am

    Thanks Bob:
    I will try the C-17X in there I just ordered two of them on this advice as I have enough space for them. I also have enough space to mount bigger transformers is there any advantage to going to say the M-125 type trannies here. I am working on making this amp as robust as possible and if there is any gain with the trannies are you amenable to selling a set of them?
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    Bob Latino
    Bob Latino
    Bob Latino
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    Posts : 3276
    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°4

    ST-120 choke substitution Empty Re: ST-120 choke substitution

    Post by Bob Latino Tue Jan 17, 2012 10:44 am

    baddog1946 wrote:Thanks Bob:
    I will try the C-17X in there I just ordered two of them on this advice as I have enough space for them. I also have enough space to mount bigger transformers is there any advantage to going to say the M-125 type trannies here. I am working on making this amp as robust as possible and if there is any gain with the trannies are you amenable to selling a set of them?

    Hi George,

    The VTA ST-120 trannies have been tested up to 90 watts continuous and 120 watt peaks with no saturation. The VTA ST-120 won't deliver 90 watts continuous per channel so no worry there. You don't need the larger M-125 output trannies for a custom ST-120 build ..

    Bob
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    • Post n°5

    ST-120 choke substitution Empty Re: ST-120 choke substitution

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