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    Testing a stock Dynaco ST-70 - video ..


    Bob Latino

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    Join date : 2008-11-26
    Location : Massachusetts

    Testing a stock Dynaco ST-70 - video ..

    Post by Bob Latino on Fri Feb 15, 2013 8:52 pm

    Below is a test of a stock Dynaco ST-70 video done by El Paso Tube amps. It is interesting to watch. The amp was rebuilt with a new stock type driver board and tested for frequency response, distortion and power output. If you have any comments post them in this thread ..



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    Re: Testing a stock Dynaco ST-70 - video ..

    Post by PeterCapo on Sat Feb 16, 2013 11:39 am

    We must have caught each other’s thought waves, Bob, as I just so happened to watch this very video yesterday! I have always felt that the original circuit performed reasonably well.

    I think this video may demonstrate that a commonly held belief about the original’s low frequency performance limitations might be overstated. For instance, it didn’t start running out of gas until the frequency went down to 20Hz. The original circuit’s performance here would probably only be an issue with a minority of recordings that go down that low, and in most systems that the amp would be used in, would the speakers even be capable of such low frequencies?

    And, this video makes a case for not using (in a Stereo 70) the popular CL90 thermistor, which is rated for 2 amps. I have always said that if you are going to use a thermistor in the PT primary, its maximum current rating should at least equal the line fuse value.

    But, I don’t think a fair comparison can ever be made against an original sample with the original parts. If you take one and refresh it with new parts and build-in a few enhancements (like a bolstered power supply with low esr capacitors) that some of the various mods enjoy, then the original design becomes a viable choice that may just end up being a matter of personal taste. Of course, in saying this, I do not by any means intend to denigrate any of the many replacement circuits available. I just think the original circuits are still a viable choice and deserve a fair chance on an even playing field.

    Last edited by PeterCapo on Sat Feb 16, 2013 7:08 pm; edited 3 times in total


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    Re: Testing a stock Dynaco ST-70 - video ..

    Post by tubes4hifi on Sat Feb 16, 2013 3:28 pm

    check out his other video here, go to the 11 minute point where he is looking at our VTA M125 amp.

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    Re: Testing a stock Dynaco ST-70 - video ..

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