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    My 2nd ST70

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    kaner

    Posts : 88
    Join date : 2011-09-20

    My 2nd ST70

    Post by kaner on Wed Feb 01, 2012 12:04 am

    I came upon an old ST70 that had really been neglected, and was able to buy it for $150. The chassis was bad but not terrible, the quad cap had clearly been leaking, the output transformers were long gone, the power transformer was rusty and the power cord was missing. It did have 4 EL34's and a rectifier tube. I put it in my shop and started accumulating parts. Having already built a VTA that I was really happy with I bought a blank PCB from Roy and scrounged around for parts.

    As I found parts I put them in here and there, and eventually ordered the missing parts from Digikey and the OPT's from Dynakitparts.com. I finally finished it this morning, crossed my fingers and ran it up on the variac. I am happy to report that the power transformer is fine, the rectifier glowed and 3 of the 4 EL34's lit up. The cleaned up chassis is not beautiful but it's presentable. It needs to burn in (I used the Russian PIO's) but it sounds great.

    Here is my question. What should I do with it? Should I biamp my speakers? Should I wire in some rear speakers and drive them with the 2nd amp? Should I run it as a separate system in my workroom (seems like overkill, I've always just had an old radio)? I do not want to sell it because I feel like I rescued it from the dead. Anyway, it's a nice problem to have.


    GP49

    Posts : 717
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: My 2nd ST70

    Post by GP49 on Wed Feb 01, 2012 12:12 pm

    kaner wrote:
    Here is my question. What should I do with it?

    That's easy. Send it to me. What a Face

    CONGRATULATIONS on saving an ST-70 and making it sing again!

    kaner

    Posts : 88
    Join date : 2011-09-20

    Re: My 2nd ST70

    Post by kaner on Sun Feb 05, 2012 12:04 am

    Ok, it's on its way! Seriously has anyone tried using a 2nd ST70 to enhance their system? Have you used it to biamp? Drive a second set of speakers?


    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: My 2nd ST70

    Post by Bob Latino on Sun Feb 05, 2012 8:47 am

    Hi Kaner,

    I have biamped here in my downstairs system with two VTA ST-120's on some Magnepan speakers. I now use two VTA M-125's on these Magnepan MG 3.6R's



    Below is a photo of someone using two VTA ST-70's to biamp a pair of Tyler Acoustics Linbrook II speakers



    Biamping with two amps will give you 3 dB more volume and/or "headroom". Biamping also gives greater signal isolation between the two channels as long as you vertically biamp with one amp on each stereo channel. This greater signal isolation usually translates into better soundstaging. Some people horizontally biamp. Horizontally biamping is when you have one amp on the woofer sections of each or the two speakers (usually a large solid state amp) and one amp on the two tweeter sections. If you use two TUBE amps the vertical method is better - one amp on each stereo channel.

    Bob

    kaner

    Posts : 88
    Join date : 2011-09-20

    Re: My 2nd ST70

    Post by kaner on Sun Feb 05, 2012 10:07 am

    Thanks Bob. Vertical biamping would never have occurred to me. I guess that means I should have built the two amps identically. Instead the first uses the components from VTA and transformers from Dynakitparts. The second uses the original power transformer and choke, Russian PIO's and different tubes. Any thoughts?


    Thanks

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: My 2nd ST70

    Post by Bob Latino on Sun Feb 05, 2012 10:45 am

    Ideally the two amps should be identical but they may be both close enough to the point where you may not notice much difference in sound quality between them ...

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