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    Questions about the SCA 35

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    sailor

    Posts : 269
    Join date : 2011-04-04

    Questions about the SCA 35

    Post by sailor on Thu Sep 29, 2011 2:41 pm

    I bought a very clean and all original, [except for the tubes], Factory Built SCA 35. The power transformer had a date of 10/63 and all transformers had cloth leads. I think that makes the transformers American made. I have a few questions.
    R37 is the feedback resistor with a value of 82,000, correct color code, they both tested about 585 ohms. Is this because they are in parallel with part of the output transformer or is there a problem?
    I know this is not a problem but one of the original cap. is listed in the manual as .1MFD at 250 volts but was 1.0 mfd at 250 volts on this amp and was shown to be 1 MFD on one piece of the paper work, did they change this to .1 in later units?
    This is a very clean and original amp, what can I do to the output boards without lowering the value to a collector. Like remove the 16 volt coupling cap, or change out the other caps, or update the resistors. Or should I leave well enough alone? I probably will want to sell it in the near future as I intend to purchase a VTA 120 kit in Nov. so I don't want to lower the value.
    Yes it is a SCA with 7199's not a ST.

    GP49

    Posts : 718
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Questions about the SCA 35

    Post by GP49 on Fri Sep 30, 2011 12:09 am

    You're going to sell it in two months. Do nothing but clean it up. An original, factory wired Dynaco will get you less money if you do any modifications.

    sailor

    Posts : 269
    Join date : 2011-04-04

    Re: Questions about the SCA 35

    Post by sailor on Thu Oct 06, 2011 3:55 pm

    Does anyone know the answer to the resistor and cap questions above? Also the SCA has a lot more room below than the ST, If I change out the caps can I mount them under the board like the VTA stereo 70 board?

    GP49

    Posts : 718
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Questions about the SCA 35

    Post by GP49 on Fri Oct 07, 2011 12:20 am

    sailor wrote:
    R37 is the feedback resistor with a value of 82,000, correct color code, they both tested about 585 ohms. Is this because they are in parallel with part of the output transformer or is there a problem?
    .

    There is probably no problem with the feedback resistor. R37 in *series* with the secondary of the output transformer is parallel with R31 (560Ω). To accurately measure the feedback resistor you will need to lift one end before measuring.

    sailor wrote:
    I know this is not a problem but one of the original cap. is listed in the manual as .1MFD at 250 volts but was 1.0 mfd at 250 volts on this amp and was shown to be 1 MFD on one piece of the paper work, did they change this to .1 in later units?

    I don't know earlier vs. later but if you were to look at the schematic and the construction manual for the SCA-35 on this site, one shows C18 as 0.1 mfd, the other shows it as 1 mfd. If it's what came in the unit from the factory and the unit is functioning properly, I'd say to follow the advice of the late Bob Tucker at Dynaco: "LET SLEEPING AMPLIFIERS LIE."



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