The Dynaco Tube Audio Forum

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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

    M125 No sound

    rwbaker
    rwbaker
    rwbaker


    Posts : 3
    Join date : 2021-01-20
    Age : 63
    Location : DFW Texas
    • Post n°1

    M125 No sound Empty M125 No sound

    Post by rwbaker Tue Dec 13, 2022 12:35 am

    Power switch was cycled too fast and apparently took out the rectifier. Installed Mullard NOS Z33 and compared voltages against Bob's specs under initial startup in the instructions. Here are the results:
    V5 #4 = 20VAC
    #6 = 420VAC
    #2 = 495VDC
    #8 = -4VDC

    Does this mean the power transformer is out? Thanks for the help. I love the amps and love even more learning about analog circuits.

    Rick
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    Bob Latino
    Bob Latino
    Bob Latino
    Admin


    Posts : 3277
    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°2

    M125 No sound Empty Re: M125 No sound

    Post by Bob Latino Tue Dec 13, 2022 9:19 am

    rwbaker wrote:Power switch was cycled too fast and apparently took out the rectifier. Installed Mullard NOS Z33 and compared voltages against Bob's specs under initial startup in the instructions.  Here are the results:
    V5 #4 = 20VAC
    #6 = 420VAC
    #2 = 495VDC
    #8 = -4VDC

    Does this mean the power transformer is out? Thanks for the help.  I love the amps and love even more learning about analog circuits.

    Rick

    Hi Rick,

    Pins 2 and 6 are normal ranges but pins 4 and 8 are low.. You may have taken out one side of the high voltage winding by cycling the on off switch too quickly. Pull out the rectifier (leave the other tubes in) and measure the AC voltage on pins 4 and 6 again to chassis ground. They should both be in the 390 AC to 430 AC range.

    Bob
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