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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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daveshel
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    sca 35 rebuild

    Paul229
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    Paul229


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    • Post n°1

    sca 35 rebuild Empty sca 35 rebuild

    Post by Paul229 Wed Jan 20, 2016 5:32 am

    Just got the Dynaco sca 35

    All original

    It needs some other parts after all those years

    Where to start ........

    The output transformers of this one the same as in the ST70 ....?

    Thanks all

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    Bob Latino
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    • Post n°2

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by Bob Latino Wed Jan 20, 2016 9:49 am

    Paul229 wrote:Just got the Dynaco sca 35

    All original

    It needs some other parts after all those years

    Where to start ........

    The output transformers of this one the same as in the ST70 ....?

    Thanks all


    The output transformers on the Dynaco SCA-35 are the same as on the Dynaco ST-35 not the ST-70. If you need any parts for your SCA-35 check with Kevin at dynakitparts.com ...

    Bob
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    peterh
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    • Post n°3

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by peterh Wed Jan 20, 2016 10:06 am

    Paul229 wrote:Just got the Dynaco sca 35

    All original

    It needs some other parts after all those years

    Where to start ........

    The output transformers of this one the same as in the ST70 ....?

    Thanks all

    if it ain't broken, don't mess with it with one exception :
    install the EFB kit "http://www.tronola.com/html/daves_store.html" which replaces
    the B+ cap and in addition controls the bias in an intelligent way. This increases
    power and reduced distorsion. Highly recommended.

    Things that might be time to replace : 7199 tubes. They are still available ( at premium
    prices), but if need to replace 6u8 tubes + an adapter can be used as substitution.
    Or, if more money is sinked; get the replacement boards from dave's store, they are
    ready for 6u8 .

    EL84 tubes, you might have good ones, but if you replace, make shure you get a matched quartet.

    Enjoy!
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    Paul229
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    • Post n°4

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by Paul229 Thu Jan 21, 2016 6:49 am

    Thank you all

    I start with the EFB board
    Seems very efficient.

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    Paul229
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    • Post n°5

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by Paul229 Fri Jan 22, 2016 12:27 pm

    Why the   output transformers  of the ST 70 a.o.  are so much better then recent made f/e at Hammond

    Seems less  attention to detail or materials o.a. skill

    Are the outputs of the St70 the same as in the 35 and or.......?

    Really appreciate the ST70 outputs

    ..Could it be that the output transformers of Dynaco are getting better as years go by....?


    Last edited by Paul229 on Sat Jan 23, 2016 10:23 am; edited 3 times in total
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    corndog71
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    • Post n°6

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by corndog71 Fri Jan 22, 2016 1:41 pm

    SCA35 and ST35 use a PA-774 power transformer and Z-565 output transformers.

    ST70 is a different amp that uses a PA-060 power transformer and A-470 output transformers.

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    denny9167
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    • Post n°7

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by denny9167 Fri Jan 22, 2016 6:32 pm

    I would simply use one cathode resistor for each pair of EL84 tubes, approximately 190ohms, beef up the power supply ex: more capacitance, IE: replace Filter Caps!! and you will have a killer integrated! Some mods needed on the Phono board, but that may be for another discussion.
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    daveshel
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    • Post n°8

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by daveshel Sun Jan 24, 2016 3:07 pm

    If you need a set of 7199s I have a set in the for sale thread and I just lowered the price.
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    Paul229
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    • Post n°9

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by Paul229 Sun Jan 24, 2016 3:24 pm

    At the back there is the wire connections for speakers

    the 1ste one is interconnected with a funny wire

    Should those two be connected...?


    Last edited by Paul229 on Tue Jan 26, 2016 4:04 pm; edited 1 time in total
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    • Post n°10

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by Paul229 Tue Jan 26, 2016 3:28 pm

    Notice


    After playing one output transformer is warm as warm as the main transformer at the back
    The other one stays rather neutral


    The one in the Centre of my Sca 35 stays without  higher temperature

    Can you check if that is normal or is it a warning for trouble..

    Thanks for looking
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    Bob Latino
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    • Post n°11

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by Bob Latino Tue Jan 26, 2016 6:07 pm

    Paul229 wrote:At the back there is the wire connections for speakers

    the 1ste one is interconnected with a funny wire

    Should those two be connected...?

    Paul,

    See if you can post a photo of the wiring on the forum here ... (check the sticky above on how to post a photo) We can take a look at it and maybe one of us can figure why your amp does not play correctly ...

    Bob
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    peterh
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    • Post n°12

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by peterh Wed Jan 27, 2016 2:50 am

    Paul229 wrote:At the back there is the wire connections for speakers

    the 1ste one is interconnected with a funny wire

    Should those two be connected...?
    Yes, there should be a wire connecting the 2 leftmost ( viewed from the back) terminals.
    This is for a center speaker. See the manual p.5
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    Paul229
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    • Post n°13

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by Paul229 Wed Jan 27, 2016 4:05 am

    Okay Thanks

    You know why one output transformer is getting warm while the other one stays room temperature does not warm up at all...

    This unit was out of business for 30 years so maybe there is something i do not consider
    Have to keep a close watch on what is going on

    I do not like one is hot /warm the other one just room temperature.....
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    peterh
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    • Post n°14

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by peterh Wed Jan 27, 2016 5:35 am

    Paul229 wrote:Okay Thanks

    You know why one output transformer is getting warm while the other one stays room temperature does not warm up at all...

    This unit was out of business for 30 years so maybe there is something i do not consider
    Have to keep a close watch on what is going on

    I do not like one is hot /warm the other one just room temperature.....

    Use normal fault location procedures ...

    a suggestion :
    1/ swap the el84 tubes between the channels ( move the pair from one board to the other )
    see if the same transformer gets hot.

    2/ if the fault follows the tubes : but a quad of new tubes
    if the fault stays, disconnect the hot transformer and prepare to examine
    ( i'll come back with exact procedures), but prepare to purchase a new one from dynakitparts)

    It might also be a circuit malfunction, examine with a scope the two channels before
    and after swapping tubes. Look for oscillations.

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    Paul229
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    • Post n°15

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by Paul229 Thu Jan 28, 2016 6:01 am

    okay do  that

    Other tubes no difference at all>

    Something is going on and cannot lay my hands on it... so need further measures


    -  I leave these boards in there and original -

    They are with AB resistors better then the ones on a new board

    ..Only change the 0,1 and 1.uF caps 8 caps of which the two green 0,1uf 16V on C17 are the worst ........
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    • Post n°16

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    Post by Paul229 Mon Mar 14, 2016 3:43 am

    Replaced the two Aerovox caps in power supply

    But ran a problem second Capacitor
    C 23 Lug  
    (1)  320v
    2   250v

    Pin 1 is connected with a 22K to pin 2 of the aerovx 50/50uF

    Giving it 150v

    Schematics says 250v

    Which one is right ...the 22k resistor in there.....to follow- or the schematics...?
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    peterh
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    • Post n°17

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by peterh Mon Mar 14, 2016 5:26 am

    Paul229 wrote:Replaced the two Aerovox caps in power supply

    But ran a problem second Capacitor
    C 23 Lug  
    (1)  320v
    2    250v

    Pin 1 is connected with a 22K to pin 2 of the aerovx 50/50uF

    Giving it 150v

    Schematics says 250v

    Which one is right ...the 22k resistor in there.....to follow- or the schematics...?

    What schematics ? Are you NOT installing the EFB board as you said you should ?
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    Paul229
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    • Post n°18

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by Paul229 Mon Mar 14, 2016 3:57 pm

    No not needed

    Amp is good with upgrades.

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    peterh
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    • Post n°19

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by peterh Mon Mar 14, 2016 5:18 pm

    Paul229 wrote:No not needed

    Amp is good with upgrades.


    I think you make a mistake here. EFB is one of the refinements that actually does something. But as you already have invested in caps and work you have lost this battle.
    But i agree , sca35 is one hell of an amp for it's cost!

    BTW, did you solve the hot and cold OT issue ?
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    GP49
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    • Post n°20

    sca 35 rebuild Empty Re: sca 35 rebuild

    Post by GP49 Mon Mar 14, 2016 10:11 pm

    I agree. The EFB circuit is miles beyond any level of tube rolling and upgrading of capacitors and passive parts, no matter how expensive. It puts the output stage into a considerably more linear, lower distortion mode of operation.
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