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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


3 posters

    Finally got my VTA ST 70 rolling

    Midwestside
    Midwestside
    Midwestside


    Posts : 78
    Join date : 2019-03-20
    • Post n°1

    Finally got my VTA ST 70 rolling Empty Finally got my VTA ST 70 rolling

    Post by Midwestside Mon Apr 20, 2020 5:23 pm

    Well some of you may remember I had bought a vta st 70 last year and had a few problems with it.
    Blowing rectifiers and fuses, etc.
    I finally decided to go back in and beef up all solder joints, bought a new quad of svetlana el 34s and a matsushita 5ar4 tube.
    Fired it up, set the bias and now listening to some sweet sounds.
    Glad i didn't give up and sell it! Thanks PeterCapo! (if you remember that)  Very Happy

    Finally got my VTA ST 70 rolling Photo_11


    Last edited by Midwestside on Mon Apr 20, 2020 7:34 pm; edited 1 time in total
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    Bob Latino
    Bob Latino
    Bob Latino
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    Posts : 3276
    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°2

    Finally got my VTA ST 70 rolling Empty Re: Finally got my VTA ST 70 rolling

    Post by Bob Latino Mon Apr 20, 2020 5:55 pm

    Hi John,

    Glad to hear that you are up and running .. The most common issues with kit amps are bad solder connections. Most people think "I made a wiring error ?" but that is not true. Also > bad solder connections usually show up after a period of time - sometimes a year or more down the road. What happens is that the amp goes through a number of heat up and cool down cycles and the solder connections expand and contract many times. After a while a solder connection may go "partial" and maybe you lose a channel or you start to get "staticky" or crackle noises usually on just one channel. This sounds like a "shotgun approach" but many times the cure is to just resolder every connection on that channel. If you use enough heat with your soldering device, bad solder connections are usually not a problem.

    Bob
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    Midwestside
    Midwestside
    Midwestside


    Posts : 78
    Join date : 2019-03-20
    • Post n°3

    Finally got my VTA ST 70 rolling Empty Re: Finally got my VTA ST 70 rolling

    Post by Midwestside Mon Apr 20, 2020 6:19 pm

    Thanks Bob.
    In the meantime i have acquired better soldering skills and understanding of tube amps.

    Couple of questions.

    I'm using a variac at 117 vac to run the amp. Does the variac need to be the only thing in a wall socket feeding the amp? or can i incorporate a power strip before or after?

    Is it dangerous to fine tune the bias with a signal going through the amp?

    I have a back up Old gz34 mullard. I noticed on another thread you mention gz33 or gz37 working. Do you prefer those over the gz34 sonically?


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    Bob Latino
    Bob Latino
    Bob Latino
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    Posts : 3276
    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°4

    Finally got my VTA ST 70 rolling Empty Re: Finally got my VTA ST 70 rolling

    Post by Bob Latino Mon Apr 20, 2020 7:04 pm

    Midwestside wrote:Thanks Bob.
    In the meantime i have acquired better soldering skills and understanding of tube amps.

    Couple of questions.

    I'm using a variac at 117 vac to run the amp. Does the variac need to be the only thing in a wall socket feeding the amp? or can i incorporate a power strip before or after?

    Is it dangerous to fine tune the  bias with a signal going through the amp?

    I have a back up Old gz34 mullard.  I noticed on another thread you mention gz33 or gz37 working. Do you prefer those over the gz34 sonically?



    The variac could be plugged into a power strip.

    The bias should be set with the amp at idle (no signal going through the amp) and in the pentode ultralinear mode

    The GZ33 and GZ37's still out there are getting pricey because they are not made anymore. There is minimal differences in sound between rectifiers as long as each rectifier is operating properly. The GZ33 and GZ37 were much better made and would be longer lasting than any presently made GZ34/5AR4.

    Bob
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    wildiowa
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    wildiowa


    Posts : 237
    Join date : 2012-03-19
    • Post n°5

    Finally got my VTA ST 70 rolling Empty Re: Finally got my VTA ST 70 rolling

    Post by wildiowa Mon Apr 20, 2020 8:32 pm

    You can run the power strip out of the Variac and give all your components a little more headroom. The voltage should remain the same even if you run pre amps and other stuff off the strip. Most modern components don’t seem to have any problems with higher line voltages.
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    Finally got my VTA ST 70 rolling Empty Re: Finally got my VTA ST 70 rolling

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