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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


    SCA 35 Output Transformer

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    jwb474

    Posts : 26
    Join date : 2014-07-13

    SCA 35 Output Transformer Empty SCA 35 Output Transformer

    Post by jwb474 on 15th March 2015, 11:34 am

    I am starting to move forward on my SCA 35 project and wanted to changed the output transformers in order to go from 8 and 16 ohm to 4 and 8 ohm. My question is this: Is the feedback resistor and capacitor which was optimized for the 16 ohm output level and impedance of the original transformer OK for the new transformer? I had sent a request to Dynakitparts.com a few weeks back, but have not got a response.
    peterh
    peterh

    Posts : 1352
    Join date : 2012-12-25
    Location : gothenburg, sweden

    SCA 35 Output Transformer Empty Re: SCA 35 Output Transformer

    Post by peterh on 15th March 2015, 11:46 am

    jwb474 wrote:I am starting to move forward on my SCA 35 project and wanted to changed the output transformers in order to go from 8 and 16 ohm to 4 and 8 ohm. My question is this: Is the feedback resistor and capacitor which was optimized for the 16 ohm output level and impedance of the original transformer OK for the new transformer? I had sent a request to Dynakitparts.com a few weeks back, but have not got a response.
    You refer to R37 ( 82k ) ? Try 47k. The cap C21 you need a scope and make it as big as
    preventing overshoot when feeded with squarevawes. 12 pF could be a good starting point.
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    jwb474

    Posts : 26
    Join date : 2014-07-13

    SCA 35 Output Transformer Empty Re: SCA 35 Output Transformer

    Post by jwb474 on 15th March 2015, 11:55 am

    You refer to R37 ( 82k ) ?  Try 47k.   The cap C21 you need a scope and make it as big as
    preventing overshoot when feeded with squarevawes. 12 pF could be a good starting point.[/quote]

    Yes. 47K does make sense since the max voltage is 1/2 of what it was. I do have the equipment to test the amp. On a related note, has anyone here used Virtins Technology's multi-instrument software? I am trying it out and it appears to be great for a hobbyist.
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    jwb474

    Posts : 26
    Join date : 2014-07-13

    SCA 35 Output Transformer Empty Re: SCA 35 Output Transformer

    Post by jwb474 on 15th March 2015, 11:57 am

    jwb474 wrote:You refer to R37 ( 82k ) ?  Try 47k.   The cap C21 you need a scope and make it as big as
    preventing overshoot when feeded with squarevawes. 12 pF could be a good starting point.

    Yes. 47K does make sense since the max voltage is 1/2 of what it was. I do have the equipment to test the amp. On a related note, has anyone here used Virtins Technology's multi-instrument software? I am trying it out and it appears to be great for a hobbyist.[/quote]
    peterh
    peterh

    Posts : 1352
    Join date : 2012-12-25
    Location : gothenburg, sweden

    SCA 35 Output Transformer Empty Re: SCA 35 Output Transformer

    Post by peterh on 15th March 2015, 1:30 pm

    jwb474 wrote:
    jwb474 wrote:You refer to R37 ( 82k ) ?  Try 47k.   The cap C21 you need a scope and make it as big as
    preventing overshoot when feeded with squarevawes. 12 pF could be a good starting point.

    Yes. 47K does make sense since the max voltage is 1/2 of what it was. I do have the equipment to test the amp. On a related note, has anyone here used Virtins Technology's multi-instrument software? I am trying it out and it appears to be great for a hobbyist.
    [/quote]
    It's more 1/sqrt(2) Thus 47 - 56 k is what you need as R37
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    rmyauck

    Posts : 9
    Join date : 2012-02-18

    SCA 35 Output Transformer Empty Re: SCA 35 Output Transformer

    Post by rmyauck on 18th March 2015, 1:56 pm

    If it were me I would keep the vintage OPT's due to their well regarded sonics and try them with your speakers on the different taps with no regard to worrying about them not being matched. I think you will be pleasantly surprised!

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    SCA 35 Output Transformer Empty Re: SCA 35 Output Transformer

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