Dynaco Stereo 70 (1959–1976)

A vacuum tube power amplifier that became the best-selling tube amp of all time.

Overview

The Dynaco Stereo 70 is a vacuum tube power amplifier introduced in 1959 by Dynaco, designed by David Hafler. It was one of the most famous and widely used tube amplifiers ever made, selling over 350,000 units during its 17-year production run. Marketed primarily as a kit (Dynakit), it offered exceptional value and performance, becoming the gateway to tube audio for generations. The amplifier was available in both kit and factory-wired forms, with the assembled version priced at $130 at launch. It formed part of a complete high-fidelity system when paired with the PAS-3 preamplifier and FM-3 tuner, which together cost under $200.

Specifications

Power output	35 watts per channel
Frequency Response	20Hz–20kHz (±1dB)
THD	0.5%
Damping factor	20
Input sensitivity	1.5V
Input impedance	200k ohms
Output impedance	4, 8, 16 ohms
Dimensions (W×H×D)	13" × 4-3/4" × 9-1/2"
Weight	26 lbs
Tubes	7199 (phase splitter/driver), EL34 (output)
Circuit configuration	push-pull ultralinear

Design

The Stereo 70 uses a push-pull ultralinear circuit configuration with a 7199 tube as the phase splitter/driver and a pair of EL34 output tubes per channel. It features a simple, reliable design with high-quality transformers, contributing to its clean sound and long-term durability.

Context

Designed by David Hafler and introduced in 1959, the Stereo 70 was a response to the rise of stereo records. It became the best-selling tube amplifier in history and remained the most popular vintage tube amp for restoration and modification. The Mark IV monoblock was essentially one channel of the Stereo 70, and the PAS-3 preamplifier served as its companion. A second generation, the ST70 II, was later introduced.

Market

The Dynaco Stereo 70 remains highly sought after, with original unmodified units listed around $1,099 and restored or modified versions priced between $900 and $1,800. It is known for reliability but has a documented tendency for output stage failures, with many units requiring restoration over time.