Dynaco ST-70 Series 3 Tube Amplifier Review

[Doodski]

What part of participating here involves meeting people in person?

People have opened invitations as they visited different cities or attempted rounding up a few members to meet but nothing really serious yet.

 

[dlaloum]

One of my first systems. Note the date.
View attachment 379465

Nice Empire TT too...

 

[Sal1950]

What part of participating here involves meeting people in person?

Well I didn't believe you meant that "in person" figuratively.
Try an audio show or join a local club, great social events to meet others of like interests.

 

[Petrushka]

People have opened invitations as they visited different cities or attempted rounding up a few members to meet but nothing really serious yet.

What I said was, I haven’t met, in person, any audiophiles.

 

[Mart68]

What part of participating here involves meeting people in person?

Not mandatory but in the UK we often have meets, either at a rented venue or someone's house.

Obviously UK is only about size of New York state so bundling some kit into a car for a few hours drive isn't a big deal. No-one is unfeasibly far from anyone else. Not so easy if in a country the size of the USA.

 

[motorstereo]

What I said was, I haven’t met, in person, any audiophiles.

Interesting; apparently you've never bought any new gear from a stereo shop back in the day or browsed their record selection where you're surrounded by audiophiles who like to chat. Heck even the salespeople in the industry are audiophiles.

 

[Petrushka]

Interesting; apparently you've never bought any new gear from a stereo shop back in the day or browsed their record selection where you're surrounded by audiophiles who like to chat. Heck even the salespeople in the industry are audiophiles.

With the exception of a couple of AVRs, I shopped at estate sales and garage sales. Got to try hundreds of pieces.

Circuit City and Best Buy drove out all the dealers, except for the custom installers.

 

[leebergtally]

I have heard incredibly heroic attempts at LP playback at audio shows. We are talking both vintage and and modern > $50,000 turntables. Rarely am I impressed with such playback experiences. On the other hand, master tapes from the era are excellent and clearly superior to any digital

I found a recording of “In a Persian Marketplace” by Sammy Davis Jr. at the George Blood Digitized 78 RPM collection at the Internet Archive. I was looking for the most recent 78’s that overlapped the dawn of LP’s. I wanted to see if the 78’s higher write and read speed would result in an audiophile quality recording (especially if both 78 and LP were mastered from the same tape). That recording was the best sounding 78 transfer I could find in terms of distortion, frequency response (subjective) and noise. If I didn’t know better I’d have thought it was an LP. All this was I believe due to the excellent condition of the record and Mr Blood’s four simultaneous tonearm transfer technique. You can read about it at George Blood Process. Unfortunately it was deleted in a recent copyright infringement purge. I did download the best quality FLAC version and will post a link soon.

 

[leebergtally]

I found a recording of “In a Persian Marketplace” by Sammy Davis Jr. at the George Blood Digitized 78 RPM collection at the Internet Archive. I was looking for the most recent 78’s that overlapped the dawn of LP’s. I wanted to see if the 78’s higher write and read speed would result in an audiophile quality recording (especially if both 78 and LP were mastered from the same tape). That recording was the best sounding 78 transfer I could find in terms of distortion, frequency response (subjective) and noise. If I didn’t know better I’d have thought it was an LP. All this was I believe due to the excellent condition of the record and Mr Blood’s four simultaneous tonearm transfer technique. You can read about it at George Blood Process. Unfortunately it was deleted in a recent copyright infringement purge. I did download the best quality FLAC version and will post a link soon.

I thought I had the the Sammy Davis Jr. recording of In a Persian Marketplace, but I was not able to locate it on any of my hard drives. I did find a version of it here The Albert Ketelbey Archives Historical 78 Recordings I think it's been processed and restored, but it's a great example of how good some 78's could sound. I recorded the output of my computer to a Zoom recorder and have posted on DropBox In a Persian Market Place, Sammy Davis Jr

 

[rjp]

I bought one of these amps when they were clearing then out new for 1500 and I love it. Probably the best sounding amp I have ever listened too. I do use the built in HPF option and have the bass handled by a sub and that really frees up the Dynaco to do what it does best. I'm not surprised it measures poorly relative to modern SS standards of accuracy.

 

[rjp]

This might shed some light on why they chose 12AU7. From their design team via a review on the Absolute Sound
"The first challenge involved the obsolete 7199 pentode-triode. There have literally been dozens of DIY-inspired upgrades attempted over the years aimed at replacing the original front end. Radial Engineering selected three input/phase-splitter circuits for extensive testing using various tube configurations. The first recreated the original design using a pair of EF86 small-signal pentodes and a 12AU7 dual triode as the phase-splitter, even though there was concern over the limited availability of the EF86. The two other circuits evaluated were all triode, based on circuits designed by Hafler over his long career. The first of these used a 12AX7 voltage amplifier and a pair of 12AU7 as long-tailed-pair phase-splitters. The practical issue with the long-tail-pair phase-splitter was the need for a trimmer adjustment for proper balance. The third circuit was derived from a Williamson design by Hafler that was not sold commercially for cost reasons. It uses a 12AU7 dual triode as a voltage amplifier and cathodyne phase-splitter, and another 12AU7 as an additional voltage amplifier and output tube driver. That’s a total of four 12AU7 triodes for both channels, so not surprisingly this version was dubbed the Quad Triode by the design team.
Six months were spent evaluating prototypes of all three designs using the same output transformers and power supplies. During the listening phase of the testing process, the pentode-triode design ranked lowest. And although both triode designs were comparable in midrange and treble performance, the Quad Triode nudged ahead by virtue of its punchier low end. It’s worth noting that the lower gain 12AU7 was selected instead of the common 12AX7 as the driver tube to reduce dynamic distortion levels. It also offers a lower source impedance and thus less interaction with the capacitance of the EL34’s control grid. Many years ago, David Manley opined that he could tell the IQ of a tube-amplifier designer by his choice of driver tube; a 12AX7 would score poorly in this context. Another advantage of the Quad Triode circuit is that a second feedback loop is no longer required as the cathodyne phase-splitter is buffered from the power tubes by the driver stage."
https://www.theabsolutesound.com/articles/dynaco-st-70-series-3-tube-power-amplifier/

I enjoyed reading this technical discussion of their design choices for driver circuitry. Shows they put a lot of thought and expertise into it and certainly answers the question regarding use of 12au7. Thank for sharing!

 

[TLEDDY]

OK - may I remind the hive that some of us are older (!) and did not have the advantage of modern solid state equipment.

The first hi-fi I experienced was a hand cranked RCA with a horn; hotrodding included trying needles (yes - fucking steel needles) of other materials such as bamboo!

The came tubes - wonderful, glorious thermionic emission devices that, when driving speakers of the times, simply sounded fabulous!!

Now, we have devices made of sand! Cost effective, high powered and ruler flat in response… and I now am very happy with their sound. That said. I would not trade my tube adventures from my past experience, flawed though they were.

I feel sorry for those who missed the adventure I have experienced - blown fuses, smoked transformers and heating a room with a forest of glowing tubes! I have loved every minute of the trip!

 

[EJ3]

OK - may I remind the hive that some of us are older (!) and did not have the advantage of modern solid state equipment.

The first hi-fi I experienced was a hand cranked RCA with a horn; hotrodding included trying needles (yes - fucking steel needles) of other materials such as bamboo!

The came tubes - wonderful, glorious thermionic emission devices that, when driving speakers of the times, simply sounded fabulous!!

Now, we have devices made of sand! Cost effective, high powered and ruler flat in response… and I now am very happy with their sound. That said. I would not trade my tube adventures from my past experience, flawed though they were.

I feel sorry for those who missed the adventure I have experienced - blown fuses, smoked transformers and heating a room with a forest of glowing tubes! I have loved every minute of the trip!

I never had tubes but was certainly around those that did/do. I did not really start my own audio adventure until 1974, when (at 17) I became the president of a company doing a 1/2 hour AM radio show on Sundays, introducing New (hopefully soon to get on the Top 40 Pop/Rock/Crossover) list.
We expanded to a 1 hour show, I was also the on air personality, before I left. But that kick started (in 1971 a family friend in Graz, Austria had a system that got my interest smoldering on the back burner) my HAVE TO HAVE REALLY GOOD SOUNDING STUFF AT MY HOUSE mode that I have been in ever since.

 

[rjp]

OK - may I remind the hive that some of us are older (!) and did not have the advantage of modern solid state equipment.

The first hi-fi I experienced was a hand cranked RCA with a horn; hotrodding included trying needles (yes - fucking steel needles) of other materials such as bamboo!

The came tubes - wonderful, glorious thermionic emission devices that, when driving speakers of the times, simply sounded fabulous!!

Now, we have devices made of sand! Cost effective, high powered and ruler flat in response… and I now am very happy with their sound. That said. I would not trade my tube adventures from my past experience, flawed though they were.

I feel sorry for those who missed the adventure I have experienced - blown fuses, smoked transformers and heating a room with a forest of glowing tubes! I have loved every minute of the trip!

Great perspective! For all our talk about how great modern amps and speakers are today I have no doubt that when we look back in 50 years we will laugh that we ever called this HiFi. Enjoy the ride!

 

[40th Anniversary]

How interesting, thanks to the ASR donor and for testing!

Dynaco designer Hafler created several companies. I have a Hafler amp, as original owner, on the bench for recap. Hafler was early in the parallel FET output stage.

One would assume this is a Pan Orient Corporation reproduction, now owner of the Dynaco trademark.

It was made in Canada by Radial based in the Vancouver area. I owned one a couple of years ago. A friend of mine now owns it.

 

[rjp]

It was made in Canada by Radial based in the Vancouver area. I owned one a couple of years ago. A friend of mine now owns it.

Correct. This is the company link. They don't list it anymore of course.

Pro Audio - Radial Engineering

Pro Audio products from Radial, including Direct Boxes, Splitters, Interfaces and Switchers.

www.radialeng.com