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    Next generation Dynaco

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    Dogstar

    Posts : 90
    Join date : 2014-06-23

    Next generation Dynaco

    Post by Dogstar on Sun Jul 06, 2014 9:46 am

    Greetings...
    I've been looking at the Tubes4HiFi amps and with all the research I've performed I came across this amp:

    http://www.avahifi.com/index.php?option=com_content&view=article&id=250&Itemid=235

    Though it's not a Dynaco it looks like it's heritage comes from their design.

    Is there a reason the Tubes4HiFi amp would be a better choice?

    MontanaWay

    Posts : 781
    Join date : 2014-02-06
    Age : 58
    Location : Brookings, Oregon

    Re: Next generation Dynaco

    Post by MontanaWay on Sun Jul 06, 2014 10:24 am

    by the looks of it and reading their blurb, it is an 'updated' ST70.
    Hard for me to say what it sounds like, their driver circuit only uses two tubes compared to three on the VTA, it having one input tube and two driver tubes, one for each channel.
    Their choice of power tubes is not different, pretty much standard.
    A very important point to consider are the transformers!
    The Tubes4HiFi VTA ST70 uses custom transformers with plenty of reserve, which was one of the weak points of then original ST70!
    The VTA is a proven design, has been around for a long time and sounds awesome!

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Next generation Dynaco

    Post by Bob Latino on Sun Jul 06, 2014 10:38 am

    To sum up the differences between the two amps ....

    The AVA amp in wired and tested form is $2000. The Tubes4hifi VTA ST-70 wired and tested is $1200

    The AVA ST-70 uses the old style driver circuit with just one pentode/triode driver tube per channel. The VTA ST-70 uses a much more modern driver circuit with three dual triode 12AU7 driver tubes.

    The AVA ST-70 uses the older bias system like the original ST-70 with just TWO bias pots - one per channel. The VTA ST-70 uses one bias pot per each output tube (FOUR bias pots)

    The AVA ST-70 runs in ultralinear mode only. The VTA ST-70 may be run in ultralinear or triode mode at the flick of a switch.

    The AVA ST-70 is only available in WIRED form. The VTA ST-70 is available in KIT or WIRED form.

    Bob

    Dogstar

    Posts : 90
    Join date : 2014-06-23

    Re: Next generation Dynaco

    Post by Dogstar on Sun Jul 06, 2014 10:44 am

    Thank you.

    arledgsc

    Posts : 340
    Join date : 2012-11-30
    Location : SF Bay CA

    Re: Next generation Dynaco

    Post by arledgsc on Sun Jul 06, 2014 10:54 am

    Dogstar wrote:Is there a reason the Tubes4HiFi amp would be a better choice?
    What Bob says.... I was in the process of writing up something when Bob commented...

    There are so many more driver tube possibilities with the VTA.  I really like that feature and a must have for dialing in the sound you want.  VTA is around $800 in kit form...  A real bargain.

    MontanaWay

    Posts : 781
    Join date : 2014-02-06
    Age : 58
    Location : Brookings, Oregon

    Re: Next generation Dynaco

    Post by MontanaWay on Sun Jul 06, 2014 11:20 am

    here here! pretty much a no brainer I guess :-)

    Gregg R.

    Posts : 78
    Join date : 2014-02-20
    Age : 72
    Location : Land of 11,842 Lakes

    AVA ST-70

    Post by Gregg R. on Sun Jul 06, 2014 3:48 pm

    Last Feb., I looked at Frank's take on the Dyna St-70 before I purchased Bob's VTA-70. The AVA unit would have cost me about $2200 with state tax and shipping!! I had owned some of Frank's modded gear back in the '80s, and it worked well; met the guy once, nice guy.

    But, I liked the idea of building an amp myself, saving money, and using the tubes I already had (EH6550). I don't think the AVA allows much tube choice, but it has gotten good reviews. On the other hand, it's not that tough improving on a 55 year design, esp. when you have spent 30 yrs. doing so. If you want AVA gear, you would be better off looking at his newer designs.

    Building Bob's VTA-70 just isn't that difficult! It took me about 15 hrs., which works out to $20/hr. All around, an excellent value. Click on the link below to see my build.

    As always, thanks for looking,

    Gregg R.

    VTA-70 Build


    Last edited by Gregg R. on Mon Jul 07, 2014 12:53 pm; edited 2 times in total (Reason for editing : Added link)

    Maintarget

    Posts : 209
    Join date : 2013-02-10

    Re: Next generation Dynaco

    Post by Maintarget on Sun Jul 06, 2014 4:01 pm

    I agree with all previous comments and would further add, need a little more power?
    The VTA ST-120 at 60 WPC is hard to beat in kit or built form and still cheaper.

    Dogstar

    Posts : 90
    Join date : 2014-06-23

    Re: Next generation Dynaco

    Post by Dogstar on Sun Jul 06, 2014 11:00 pm

    Gregg R. wrote:Last Feb., I looked at Frank's take on the Dyna St-70 before I purchased Bob's VTA-70. The AVA unit would have cost me about $2200 with state tax and shipping!! I had owned some of Frank's modded gear back in the '80s, and it worked well; met the guy once, nice guy.

    But, I liked the idea of building an amp myself, saving money, and using the tubes I already had (EH6550). I don't think the AVA allows much tube choice, but it has gotten good reviews. On the other hand, it's not that tough improving on a 55 year design, esp. when you have spent 30 yrs. doing so. If you want AVA gear, you would be better off looking at his newer designs.

    Building Bob's VTA-70 just isn't that difficult! It took me about 15 hrs., which works out to $20/hr. All around, an excellent value. Click on the link below to see my build.

    As always, thanks for looking,

    Gregg R.

    VTA-70 Build

    vt

    Thanks for the build album....looks good!

    deepee99

    Posts : 1333
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Next generation Dynaco

    Post by deepee99 on Mon Jul 07, 2014 12:41 pm

    If you can suck up the bucks, a pair of VTA M-125 mono-blocks should be on your radar screen. Easier to build than the stereo iterations, and they'll drive anything out there. I mean anything. Before upgrading my speaks, off the 4-ohm taps I was able to run a pair of Maggie MG2s in parallel with ESS Heils, which probably meant about a half-ohm load dip from time to time. It was a little rough on the Weber rectifiers but everything survived, thanks to Bob's proprietary xformers and conservative design.

    denny9167

    Posts : 152
    Join date : 2011-05-09
    Age : 49
    Location : Texas

    Re: Next generation Dynaco

    Post by denny9167 on Tue Jul 08, 2014 5:26 pm

    I think it makes sense to use revised driver curcuits for the Older Dynaco designs, simply because the triode-pentodes are more hard to come by. I personally haven't tried the different driver topologies, I'm sure they can sound just as good, as the older. I honestly think that it doesn't matter much which one chooses. Tubes simply do Hi-fi much better than solid state, regardless of the output class, A, AB, D or otherwise.

    deepee99

    Posts : 1333
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Next generation Dynaco

    Post by deepee99 on Tue Jul 08, 2014 5:53 pm

    denny9167 wrote:I think it makes sense to use revised driver curcuits for the Older Dynaco designs, simply because the triode-pentodes are more hard to come by. I personally haven't tried the different driver topologies, I'm sure they can sound just as good, as the older. I honestly think that it doesn't matter much which one chooses. Tubes simply do Hi-fi much better than solid state, regardless of the output class, A, AB, D or otherwise.

    I think the the transistor cranksters must be up to Class K by now.
    There are a few things you can't improve: a Ruger No. 1 single-shot rifle, and a Hafler-based Latino/Mottram tube amp and preamp. Tweak 'em (as we all do; it's like fiddling with grains of powder on the reloading bench) but don't mess with the basics.

    corndog71

    Posts : 451
    Join date : 2013-03-19
    Location : It can get windy here

    Re: Next generation Dynaco

    Post by corndog71 on Tue Jul 08, 2014 9:48 pm

    denny9167 wrote:I think it makes sense to use revised driver curcuits for the Older Dynaco designs, simply because the triode-pentodes are more hard to come by. I personally haven't tried the different driver topologies, I'm sure they can sound just as good, as the older. I honestly think that it doesn't matter much which one chooses. Tubes simply do Hi-fi much better than solid state, regardless of the output class, A, AB, D or otherwise.

    I've heard an original ST70 once before I got into tube gear. I really wasn't impressed. A few years later I heard some tube gear that changed my mind and got me to build my own single gain stage preamp. It was noisy but definitely added some of that tube magic and kept me looking for more. Eventually I picked up a used ST70 with Sound Valve 6GH8 driver board. I went through numerous tubes but for whatever reason could not get it to sound very good. (I had not heard of cap rolling at this point. It had generic Illinois caps.) My NAD 304 sounded better.

    I eventually decided to try another driver circuit and went with Joe Curcio's driver and cap upgrades. That made a significant improvement over the Sound Valves board/ quad cap. Later I got the upgraded PT and tried different coupling caps which made it even better.

    Everything I've read about the original driver circuit only confirmed my impressions of it. It was ok but can easily be beaten by modern circuits. And some modern circuits are better than others.

    Now I want to build a new ST70 similar to my ST35 & ST120. All point to point wired with film caps in the power supply.

    Gregg R.

    Posts : 78
    Join date : 2014-02-20
    Age : 72
    Location : Land of 11,842 Lakes

    VTA-70

    Post by Gregg R. on Wed Jul 09, 2014 3:46 pm

    About twenty years ago, I restored an ST-70 that had been neglected. The 7199 driver board had already been changed to one using the 6GH8. After repairing it, I got a very pleasant sounding amp like much good vintage tube sound: a rich midrange with flabby bass and rolled off highs. When I really wanted to hear what was on a record, however, I preferred my modified Adcom.

    After many, many component changes, I recently built a Bob Latino VTA-70. For me, this is pretty much the end of the road: a harmonically correct mid-range, good tight bass, and extended, but not brittle, highs, esp. with digital.*  Also, lots of tube-rolling possibilities and a reasonable price!

    As always, thanks for looking!
    Gregg R.

    *IMHO, digital NEEDS vacuum tubes!!

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