Dynaco ST-70 Series 3 Tube Amplifier Review

[Kal Rubinson]

Wow, is this a venerable design! As I recall, it was originally sold in kit form, and a lot of young, impecunious audiophiles built them to drive their AR-2's in the late '60's - early '70's. It was a pleasant sound in its day, though obviously nowhere near what can be obtained with a Wii and any decent budget speaker of today. Still, those glowing bulbs pumping out Jefferson Airplane songs looked really cool back in the day.

"Hey, man, don't keep that all to yourself. Pass it on."

One of my first systems. Note the date.

 

[Brian Hall]

Or they still sound messed up and don't make much power for how heavy they are.

Take a 2017 or later Low Rider with the 107 engine for a ride and then tell me it doesn't make enough power.

It only weighs ~650 pounds with the 1750cc engine and sounds good completely stock. My Honda NC700 weighs ~470 pounds with a 670cc engine and sounds like a sewing machine.

Sorry for the offtopic.

I don't understand why anyone would want a tube amp in 2024.

 

[restorer-john]

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

Wow, a 208/308 Empire! What is that arm (its not an Empire 98/980)? Quite a lowish mass arm for 1963.

 

[wwenze]

Nice, it's better than the NAD T758 for the majority of my listening volume

 

[Kal Rubinson]

Wow, a 208/308 Empire! What is that arm (its not an Empire 98/980)? Quite a lowish mass arm for 1963.

ADC-40 Pritchard arm.

 

[AndreaT]

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

Wow! An Empire 208! I had one in my family system, the source for PAS-3x/Stereo35 combo, driving a pair of ADC speakers…

 

[TheWalkman]

Let me think: I could buy this sketchy Dynaco or for the same money, around 40, clean, Ti 3255 based, Class D amps. I wonder what I’d do…

 

[EJ3]

But Harley Davidson's actually put out good audio and have much better torque.

Even the older Harley's would make it across country (if your butt would). They would just leave their mark where ever you parked them. And I would hope that you would have changed the drive sprockets (or have stepped up to a 5 speed trans) so that you where turning less RPM at 70 or it would feel like you had done the cross country trip twice.

 

[AndreaT]

Well, I grew up referenced to the Dynaco sound of a ST-35/PAS 3x combo and an Empire 208/Shure V15 III source: most of my peers had either no stereo or some atrocious all-in-one rig with sapphire pick-up and cheap speakers. The best system of one of my friends was a Philips integrated with possibly 10+10 watts (“dynamic power”). I cannot stress to younger readers how hard it was to find a household with a good stereo system and good habits in handling, storing and cleaning LPs. In this 1960’s early ‘70’s perspective, Dynaco offered excellent quality of amplification and RIAA equalization compared to 99% of the other systems in Northern Italy from middle, upper-middle class families. In our present times, vacuum tubes do not hold a candle to many less expensive solutions: think of the class D amplification from Hypex and any of the top ASR DAC with volume control. So, I agree 100% with Amir: no reason beyond nostalgia to buy this amp.

 

[Ron Texas]

$3k, these used to be budget gear.

 

[pavuol]

Handsome criminals yet lousy workers... [amir: no beauty contest here so permanent cage]

[fullres galleries / 1 2 ]

 

[milosz]

Years ago I saw that this thing was poised to make a comeback, announcements were made and then...nothing. A preamp was also planned.

Very nice industrial design. Disappointing electronics, though.

I would like to see what source impedance it offers to loads. Amir didn't measure it or report it. Amplifiers with high-ish output source impedances (i.e., most tube amps) cause an interesting frequency-response artifact with 2-way speakers due to Ohms law interaction between the amp's source impedance and the driver+crossover impedances. Many find this sound to be quite pleasing, and it may well be the sonic quality than some listeners describe as "tube sound" - the "sweetness" supposedly caused by euphonic distortion in tube amps is something I don't buy. Even though the THD and IM of this amp are orders of magnitude worse than solid state amps, I contend that listeners can't hear this distortion per se when listening to music. On pure tones, maybe. And if the distortion is bad enough, yeah, the music will sound distorted- but for the most part my experience has shown that even 5% THD is usually not audible when playing music.

I owned a Stereo-70, and it worked as designed. But even though in some ways it had a nice interaction with 2-way speakers, the treble range sounded.... wrong. Treble was present - it didn't sound rolled-off- but there was no texture in the treble. Hard to describe. But the effect wasn't subtle. My H-K Citation II doesn't sound like that.

 

[antcollinet]

Don't think I'll ever understand wanting this tech

I will - for me at least it is the aesthetic. But I'm not willing to pay the price of entry.

 

[AudioSceptic]

Or they still sound messed up and don't make much power for how heavy they are.

Can't resist:

"Harley-Davidson: the most efficient way yet devised of converting gasoline into noise without the side effect of noticeable horsepower."

 

[restorer-john]

Interesting review, Amir.

The power switch on the rear is just perplexing, especially as tubes get hot, really hot, and many audiophiles run their tube gear with the covers off. Reaching over to turn it off at 12 midnight...ouch! A whole bunch of trimpots and a switch on the front, but the power switch on the back??

 

[DanielT]

Thanks for the test Amir.

Pretty much as you might suspect. SINAD is not good but on the other hand not a disaster. For most people, the Dynaco ST-70 Series 3 power should be enough with more than 90 dB sensitive speakers plus active sub/bass modules. That IF you want to pay what tube amp glow costs. A good integration sub/bass module speakers can also be a challenge, but that's another question, for another thread.

Tube amp I see more for those who are good at electronics and want something that they think is fun to tinker with. Service, repair, re cap, maybe build a new tube amp from scratch and so on. The rest of us can buy a good class D amp and some candles instead if we have some cozy light to go with the sound.

 

[iraweiss]

Here is a picture from the early 1970's of my system at Indiana University. I had a Dynaco SCA-35, Dynatuner, AR turntable, Sony TC-355 tape deck and AR speakers. Half a century ago.

 

[leebergtally]

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.

Manufactured by Radial Engineering in Canada.

 

[Gorgonzola]

Question of the techies savants re. this amplifier: does it use a sold-state power supply?

I've always wondered about tube rectifiers and what possible advantages there might be for tube-based power supplies? Isn't voltage voltage?

 

[sergeauckland]

Question of the techies savants re. this amplifier: does it use a sold-state power supply?

I've always wondered about tube rectifiers and what possible advantages there might be for tube-based power supplies? Isn't voltage voltage?

One advantage of a tube-based power supply is that the HT rises slowly, as the rectifier warms up, just as all the other valves are warming up. A SS power supply has the maximum HT voltage applied immediately, before the valves start drawing current, and thus puts components (especially the reservoir and smoothing caps) under additional strain. Back in the'70s, I designed a 100 wpc valve amplifier using 6550As, with a SS power supply, but I built-in a 30-60 second time delay, and over-rated the caps so the HT wasn't applied until the valves had warmed up.

A SS supply is more efficient, in that there's no rectifier heater power wasted, and the voltage drop of a SS diode is far smaller than a valve rectifier, so much less power wasted there. It also doesn't need a centre tapped secondary or separate rectifier heater supply, so saving cost.

S