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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


    VTA-120 Problem,

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    Hops

    Posts : 53
    Join date : 2019-09-21
    Location : South Detroit, Michigan

    VTA-120 Problem, Empty VTA-120 Problem,

    Post by Hops on Sat Oct 10, 2020 9:22 am

    Hello,  
    I have a VTA-120 that had a problem this morning.    I powered it up this morning, and when the Time Delay Relay timed out and applied power,  I heard a "Chunk" through the speakers,  and the fuse on my Variac blew.    I replaced the fuse,  turned the volume to off, tried again, this time watching the amp.   TDR time Expired,  "Chunk",  and a power tube flashed.  Blew a Variac Fuse again.    I am going to pitch this quad of tubes, order some more fuses,  and order another matched quad.   Will probably open up the Amp,  do a visual inspection for blackened parts, swollen capacitors, etc. and do the Voltage checks from the assembly instructions.   Anything else I should do before powering up the Amp again?   I have noticed for awhile that the lights briefly dim whenever the TDR relay kicks in.
    Without the Amp plugged in, my Killa-Watt, plugged into the Variac, reads 118.8 -- a reasonable voltage.
    Bob Latino
    Bob Latino
    Admin

    Posts : 2959
    Join date : 2008-11-26
    Location : Massachusetts

    VTA-120 Problem, Empty Re: VTA-120 Problem,

    Post by Bob Latino on Sat Oct 10, 2020 10:42 am

    Are you using a TUBE rectifier ? If you are, that is the problem, The TDR (Time Delay Relay) should only be used with a solid state rectifier.

    Bob
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    Hops

    Posts : 53
    Join date : 2019-09-21
    Location : South Detroit, Michigan

    VTA-120 Problem, Empty Re: VTA-120 Problem,

    Post by Hops on Sat Oct 10, 2020 12:48 pm

    Using a Weber WS-1t . I have a tube rectifier, but use the copper cap. Just thought it would be more reliable / trouble free . Just Curious --- why not a Tube Rectifier with the TDR?
    Bob Latino
    Bob Latino
    Admin

    Posts : 2959
    Join date : 2008-11-26
    Location : Massachusetts

    VTA-120 Problem, Empty Re: VTA-120 Problem,

    Post by Bob Latino on Sat Oct 10, 2020 1:17 pm

    Hops wrote:Using a Weber WS-1t .   I have a tube rectifier, but use the copper cap.  Just thought it would be more reliable / trouble free . Just Curious --- why not a Tube Rectifier with the TDR?

    The TDR interferes with the normal warm up of a tube rectifier and can cause problems if you use the TDR with a tube rectifier. The output tube that flashed is probably the problem. Also check the 10 ohm 2 watt resistor on that tube socket and see if it does measure 10 ohms ?

    Bob
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    Hops

    Posts : 53
    Join date : 2019-09-21
    Location : South Detroit, Michigan

    VTA-120 Problem, Empty Re: VTA-120 Problem,

    Post by Hops on Sat Oct 10, 2020 2:07 pm

    I will check the 10 ohm relay on that channel. Actually, on all four of the power sockets. I had a 10 ohm go previously, possibly on that socket. Replaced the tube and the resistor on the previous failure. Had checked Bias the day before and all was good. Thanks for the advice. I think I will Deoxit all the power tube sockets and tension them while the Amp is down also. Also install a board cover, which I had been procrastinating on.
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    Hops

    Posts : 53
    Join date : 2019-09-21
    Location : South Detroit, Michigan

    VTA-120 Problem, Empty Re: VTA-120 Problem,

    Post by Hops on Fri Oct 16, 2020 8:07 pm

    The 10 ohm resistor at the socket with the flash is Black. Some discoloration on the stainless steel case near the resistor. Even the ground lug it is soldered to looks a little odd. I need to get a better multimeter; the self scaling feature of my EXTECH keeps changing scales in an annoying fashion.

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    VTA-120 Problem, Empty Re: VTA-120 Problem,

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