Dynaco Stereo 70 Tube Amp Reviewed

Published On: February 13, 1991
Last Updated on: October 31, 2020
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Dynaco Stereo 70 Tube Amp Reviewed

It doesn't get more classic than a Dynaco Stereo 70. You could built it yourself or buy one complete but this 35 Watt per channel amp changed audio forever. Read the classic review of the reissue from one of the most important amps ever made in audio history.

Dynaco Stereo 70 Tube Amp Reviewed

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Retro -- makes me glad to be alive. While I wasn't surprised to find Rollei and Contax exploiting nostalgia for camera collectors, or Fortis and Jaeger-LeCoultre playing to the horologists, I continue to register surprise whenever a piece of aged hi-fi equipment is Lazarus'd. After the Radford STA25 Mk IV, a couple of revived moving-coils, the (japanese) Marantz valve gear and some cabinets to turn JBL drivers into 1950s horn systems, I figured that was all we'd ever see.

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Imagine, then, my glee upon learning that one of my all-time faves, the Dynaco Stereo 70, was -- Gary Glitter-like -- back, back as a matter of fact. Said to be the best-selling valve amp of all time (according to legend, more three times as many Stereo 70s were sold than Quad IIs), the Dynaco was a humble, affordable, easy-to-assemble work-horse which probably fed sound to more American college dormitory rooms than any amp of its era. 25 years later, it's still a mover in the used amp market and still the subject of as many modifications as the Austin Seven.

Dynaco circa 1992 has nothing to do with David Hafler; the blurb describes Dynaco as 'a division of Panor Corp', about which I know nothing. But I gather that a diehard fan wrested the name and the design from the indignity its suffered since David Hafler sold the company 20 years ago. Along the way, Stereo Cost Cutters (who kept the spirit alive with parts and kits) got involved. Whatever the manouevres, the result is a bona fide Stereo 70, instantly recognizable despite new colour schemes.

It's the same 13x9.5x7in (WDH) chassis, crowned with a perforated cage, compact, utilitarian and so frill-free that 'agricultural' is the first term to spring to mind.would you believe revived moving-coils, the (J I.

Stereo 70s were sold thanof a kit ' But, in keeping with modern sensibilites and a price far higher than that of a decent second-hand original, the unit has been tarted up with an all-black finish, or a chrome-plated chassis as a #100 optional extra. Oh, and the rubber feet are new, too.

Underneath the lid, it's still recognizable, but obviously updated. For one thing, the parts quality far surpasses that of the original, and even the most fastidious of assemblers would have had to purchase superior aftermarket parts to allow an original to approach the calibre of the Series II. But it's shy a couple of valves, which suggests some solid-statery to yank the Stereo 70 into its thirtysomething decade. And these physical changes, be it due to parts availability or a well-meaning attempt to update the sound, have altered the sonic character in virtually every area.

The basic circuit has been 'largely retained', as have the legendary output transformers (the current cost of which must have contributed to the current base price of #1070 inc VAT). The output tubes are the warmly regarded EL34s, the review sample sporting superb German-made examples. Changes include new parts of far higher quality than those used in the original, which was -- after all -- designed to be affordable. Among them are precision metal-film resistors, poly-composition capacitors and power supply electrolytics which weren't even a twinkle in Radio Shack's eyes way back when the Beatles wore a silver prefix.

Filter capacitance has tripled and the power transformer is all-new and overspecified so as to run cooler than the original (which it does). The power supply is far stiffer, for definition and bass, the latter so taut as to cause alarm among anachrophiles. All of the components are mounted directly to a single double-sided motherboard, with the tube bases mounted directly to it, thus eliminating a fair bit of wiring. (The overall reduction in wiring is said to be 70%.) And the new driver tubes are Chinese 6GH8As. Best news of all is ultra-simplified user-adjustment of the bias: a screwdriver is all that's neededd, for turning two front-panel-mounted pots until the red tell-tales glow equally. So put away your AVO meter. Although the biasing employs semiconductor circuitry, the company states, in upper case, that ABSOLTELY NO SEMICONDUCTORS ARE UTILIZED IN THE AMPLIFIER SIGNAL PATH. Ahem.

Modern audiophile practices are self-evident. Hot damn: gold-plated sockets on a Dyna Stereo 70! Proper five-way binding posts...for all three impedances! Bye-bye rectifier tube, thanks to the new transformer! And hello, three-year warranty and 12 months on the tubes!

Continue reading about the Dynaco Stereo 70 tube amp on Page 2.

Hmm... This is starting to seem about as much like a Stereo 70 as a
Caterham Seven resembles Chapman's first version. The specifications,
too, are so 1990-ish that, 35W/channel rating aside, I could be writing
about any one of a dozen current amplifiers: a frequency response flat
from 20-20kHz +/-0.5db at rated power, hum and noise of -90dB, taps for
4, 8 or 16 ohms, less than 0.25% distortion. This is not a recipe for

So, what hat to wear? When I reviewed the reborn Radford, I got what
I wanted/expected: a cleaned-up Mk III with lower noise and more grunt,
but all the warmth, richness and beloved tubey-ness of its predecessor.
So unlike the original is the Stereo 70 Series II that I had to forget
about nostalgia and think of it simply as a new offering at the #1000
point. It simply cannot be compared to a vintage Dyna, pr even a
Radford STA25 Mk IV. Instead, it has to fight the wares of Croft, Audio
Innovations, Tube Technology, Michaelson Audio and anyone else with a
valve amp selling for around a grand.

Thoe only things I find romantic about this amplifier are the logo
and the styling. It's simply too controlled, too competent, too precise
and to liken to its bronzed and browned ancestor. Lots of previously
unavailable extension at both ends of the frequency spectrum make an
original sound positively compressed, while a sense of greater power
enhances both the usability and the dynamic capabilities.

It's far drier, far more solid, considerably leaner and more
detailed than the original. Try though I may I could find but one area
where it aped the oldie, and that was three-dimensionality. Not that
you'd mistake one for the other, because the Series II sounds far
bigger, the original appearing to be a three-quarter or even a
two-thirds scale model of its grandchild. But the proportions of the
soundtage are virtually identical, as are the placement of the specific
images within the soundstage.

Used with a variety of pre-amps and sources and with speakers which
it could drive without strain (the Tannoy Six Series 603, the Spendor
LS3/5a, the Genesis IM-5200), the Dyna behaved admirably, with enough
composure to allow me to forget (not that I wanted to) that I was
supposed to be in time-travel mode. The Series II sounded like what it
is: a good, modern valve amp which parks its tush somewhere inbetween
the glowing past and the solid-state present. It offers very little in
the way of clues as to the presence of six valves; only when you switch
immediately to a solid-state design do you note that the Dyna is a tad
warmer, smoother and more coherent, with few audible indications of
user abuse.

Overdriving the new Dyna is a lot like overdriving the old Dyna: it
simply shrugs and craps out without much drama. The difference is that
the Series II can be pushed a bit harder before it starts to clip, so
you can squeeze out a few more SPLs than you could with its forebear.
than an original ew more SPLs than you could from This makes it more
useable with modern speakers, with even the LS3/5A acknowledging the

But the Series II is not a safe-bet shortcut to Stereo 70 heaven. If
you want that classic sound, you have to locate a mint or merely
working original. You will want either, but not both. Chalk and cheese?
Yin and yan? Black and white? Maybe it's not quite that severe, because
both make pleasurable sounds, so they aren't quite as at odds with each
other as my reactions suggest. But it's down to expectations, and I
can't help but believe that 99% of the Series II's potential owners
will be seeking out a glimpse of the past.

Do I seem disappointed? I hope not. After all, my own Stereo 70
still works, and it would be stupid to think that those who had enough
gumption to restore the Stereo 70 to the shelves should have banked
their entire investment in nostalge. Even Fortis improved the Harwood
when that watch went back into production after 60 years in limbo. But
the new Harwood tells time with far greater accuracy than the original,
and only a yutz would suggest that that's a bad thing.

But maybe it's not the same with sound reproduction. A watch only
has to tell the time as precisely as possible. Hi-fi equipment is
supposed to seduce, amuse, charm, entertain and transport the listener,
by whatever means. The original Dynaco Stereo 70 is like your first
love. The Series II is the person you settled with after a couple of

Take your pick.buffwatch fancier it took to reach this stage,still
form of,startershe finishld have had to performedplating or
metalworkingSeries II. Andery to yank the Stereo 70 into
thirtysomethingness. But the physical changes, whether newcomponentnow
(-made)better controlwith be compared to a vintage Dyna, obe
edight,svalves; only when you switch Stefindcovet an original or a
Series IIingfor so I'm covered. 

Additional Resources
• Read more stereo amplifier reviews from HomeTheaterReview.com.
• Find an AV receiver to integrate with the amp.
• Discuss audiophile equipment on AudiophileReview.com.

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