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    Stereophile Magazine's 1992 Review of The Panor Built Dynaco ST70 II

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    kevco

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    Join date : 2009-07-16
    Location : Aldan, PA, USA

    Stereophile Magazine's 1992 Review of The Panor Built Dynaco ST70 II

    Post by kevco on Thu Aug 20, 2009 8:41 am

    http://www.stereophile.com/tubepoweramps/992dynaco/
    I stumbled across this today, I had no idea they archived such old reviews online at Stereophile...I think the review does a good job of explaining why Panor's management of the Dynaco name was generally not a success!

    Tube Nube

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    Re: Stereophile Magazine's 1992 Review of The Panor Built Dynaco ST70 II

    Post by Tube Nube on Thu Aug 20, 2009 3:50 pm

    It's good to see that stuff.

    Yeah, the Panor, I read elsewhere as well, was anaemic compared with the original.

    Love to read a head-to-head with one of the modern spec ST 70's we all know and love!

    Bob Latino
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    Re: Stereophile Magazine's 1992 Review of The Panor Built Dynaco ST70 II

    Post by Bob Latino on Thu Aug 20, 2009 4:14 pm

    Kevco,

    The ST-70 II just never caught on like the original 70 did. Maybe by 1990 audiophiles were too into solid state amps or maybe, as the reviewer mentioned, the sound quality just didn't have the "magic" of the original 70. At the end of the review he mentions that he "really can't recommend the Panor (ST-70 II)".

    One of the reason's is that the driver circuit is similar to the old 70 but uses a 6GH8A pentode/triode in place of the 7199 found on the original '70. The sound quality is about the same as the 7199 but the 6GH8A is more easily sourced than the now "extinct" 7199 tube.

    Another issue I have with this amp is that they use bandwidth limiting filters on the input to reduce the overall bandwidth in an attempt to counteract non linearities in the design of the driver circuit. In other words because the driver circuit can't respond properly to very low and very high frequencies at high volume levels - well Jeez - we'll just filter those frequencies out ! When you use an RC filter system, as is done on this amp, you introduce phase irregularities into the amp. This will usually translate into reduced soundstage depth and width and hazy placement of individual instruments in the soundstage.

    Rather than deal with the compromises in the ST-70 II, you are better off to pick up an original ST-70 and simply replace the driver board with a high quality modern all triode design driver board like the VTA driver board. This driver board is flat from 17 Hz to 30,000 Hz at rated output and doesn't resort to the use of bandwidth limiting filters.

    Bob

    GP49

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    Re: Stereophile Magazine's 1992 Review of The Panor Built Dynaco ST70 II

    Post by GP49 on Thu Aug 20, 2009 7:36 pm

    Bob Latino wrote:

    Rather than deal with the compromises in the ST-70 II, you are better off to pick up an original ST-70 and simply replace the driver board with a high quality modern all triode design driver board like the VTA driver board. This driver board is flat from 17 Hz to 30,000 Hz at rated output and doesn't resort to the use of bandwidth limiting filters.

    Bob

    That's fine as far as it goes. But even the excellent Dynaco transformers will bandwidth-limit anyway, as they don't have sufficient capacity to run full output over the entire frequency range. The output stage can feed the primaries more than they can handle linearly to the secondaries. When that happens a large feedback signal is generated and one must be careful not to saturate the input stage with feedback signal. That's probably why Panor did the bandwidth limiting in the driver stage.

    I don't know how this issue has been addressed in the various retrofit driver boards.

    Tube Nube

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    Re: Stereophile Magazine's 1992 Review of The Panor Built Dynaco ST70 II

    Post by Tube Nube on Fri Aug 21, 2009 11:02 pm

    GP,

    Are you thinking that transformers even beefier than those now available with Bob's kit could improve matters?

    GP49

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    Re: Stereophile Magazine's 1992 Review of The Panor Built Dynaco ST70 II

    Post by GP49 on Sat Aug 22, 2009 12:56 am

    Tube Nube wrote:GP,

    Are you thinking that transformers even beefier than those now available with Bob's kit could improve matters?

    Almost certainly on the low end but heavier wire and more iron for higher power handling in the lows might make a slower transformer and sacrifice performance in the highs. I've sometimes wondered if a smaller, "faster" transformer is the reason small integrated EL84 amplifiers such as the H.H. Scott LK-48 and 299 sound so good on efficient speakers that allow them to operate within their power rating.

    giottone

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    Re: Stereophile Magazine's 1992 Review of The Panor Built Dynaco ST70 II

    Post by giottone on Thu Sep 10, 2009 5:41 pm

    According to TNT-audio the Panor ST-70 ain't that bad, even better than the original in some respect. You can read it here:
    http://www.tnt-audio.com/ampli/dynaco1e.html

    GP49

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    Re: Stereophile Magazine's 1992 Review of The Panor Built Dynaco ST70 II

    Post by GP49 on Sat Sep 12, 2009 10:03 pm

    While the TNT-Audio author's subjective audio judgments may hold some validity, I have some very serious doubts about how he is handling the problem of the runaway tube, and his failed cathode resistors.

    If his amplifier was burning out cathode resistors and a tube was glowing red, something was WRONG with it!

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