The Most Popular Tube Amp in History Is Still a Classic Piece of Hi-Fi Gear

First made in 1959, this is the best-selling tube amplifier of all time.

By Tucker Bowe

Published October 2, 2024

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Updated October 2, 2024

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Dynaco hasn’t made equipment in decades. Yet it’s still a name most audiophiles know off-hand.

That’s because the American manufacturer left an indelible legacy on the world of hi-fi, thanks in large part to a single component: the Dynaco Stereo 70, or ST-70 for short.

Not only is the ST-70 regarded as one of the most popular tube amplifiers of all time, it’s still widely sought after by vintage-audio enthusiasts.

History of the Dynaco ST-70

Today, the Dynaco ST-70 is remembered as the best-selling tube amplifier. Ever.

Several factors contributed to the ST-70’s popularity but they all boil down to the fact that it was a unique audiophile-grade amplifier that was surprisingly affordable.

First released in 1959, it had a production run that lasted almost 20 years into the late ’70s. According to estimates, some 400,000 units were sold.

Dynaco ST70 tube amplifier — Like other Dynaco amplifiers, the ST-70 was sold preassembled or as a DIY kit.

Tube power

Before Dynaco, cofounder David Hafler and his childhood friend Herb Keroes started another company, Acrosound.

Notable in its own right, Acrosound is widely credited with inventing the Ultralinear transformer, which reduced distortion with its incredibly efficient design whereby the signal gets recycled through the output stage circuitry.

Years later, when Hafler helped found Dynaco in 1955 (along with Ed Laurent, not Keroes), he brought his same transformer technology and circuitry design to the new company’s amplifiers.

Uniquely, Dynaco sold its amplifiers in two different ways: preassembled or as DIY kits (called Dynakits). The latter appealed to tinkering audiophiles building their own amplifiers — as well as vintage collectors more than half a century later.

At a time when solid-slate amplifiers dominated the market, Dynaco’s tube amplifiers stood out because they were so different — in both their appearance and warm sound.

The poor man’s McIntosh

The Dynaco ST-70 was the company’s first stereo amplifier. It utilized four EL34 output tubes, one GZ34/5AR4 rectifier tube, two 7199 input (driver) tubes, two ultralinear output transformers and one power transformer.

Unlike its previous amplifiers, the Dynaco ST-70 was a low-powered tube amp. It could output 35 watts per channel (into 8 ohms), which made it compatible with a wide variety of loudspeakers, including most bookshelf speakers.

When the Dynaco ST-70 was released in the late 1950s, it represented excellent value at $99.95 — roughly $1,000 today. At the time, it was commonly referred to as a “poor man’s McIntosh.”

A modern classic

Dynaco liquidated in 1980 — primarily due to improvements in solid-state amplifiers and a 1974 FTC ruling that changed the standard way of rating amplifiers’ power levels. But the ST-70 has remained popular among vintage hi-fi enthusiasts.

(In the early 1990s, Panor Corporation — the company that acquired the Dynaco trademark — produced an updated version of the ST-70 amplifier, the Dynaco ST-70 Series II. It’s no longer manufactured but, like the original, remains a collector’s item.)

Aside from its legacy and obvious aesthetic appeal, the Dynaco ST-70 is still popular today. And because it was initially designed as DIY kit, it’s easy to restore, modify and upgrade (since most of the original components have gone out of production).

“The amp can be restored with its original design intact or, if one desires, it can be heavily modded just by removing the driver board and replacing it with one of the many modern boards available,” explained Mike Garry, owner of Hudson Valley HiFi, a NY-based audio shop that specializes in buying, restoring and selling vintage audio equipment.

“By replacing the board you essentially change the entire circuit design, and it gives you the ability to use different driver tubes than the original, difficult-to-find 7199 triode/pentode, ” said Garry. “There are many options to tube roll to change its sonic characteristics.”

Like most vintage audio equipment, original Dynaco ST-70 tube amps are rarely found in working order, though they do pop up from time to time thanks to the work of Kenny Russell at GetDynaco and shops such as Aural HiFi in Denver, CO.

Otherwise, you can purchase them from the likes of Reverb, eBay or but expect to perform some level service. The end result will likely be worth your while.