What tubes does the Dynaco ST-70 / Stereo 70 use?

The Dynaco ST-70 / Stereo 70 uses 2× 12AT7 (voltage amp / phase splitter (modern conversion)), 4× EL34 (power tubes (ultralinear push-pull)), GZ34 (rectifier).

What power tubes does the Dynaco ST-70 / Stereo 70 use?

The Dynaco ST-70 / Stereo 70 runs 4× EL34 in the output stage. Voltage-compatible alternatives include 6CA7, KT77 (always re-bias before swapping).

What rectifier tube does the Dynaco ST-70 / Stereo 70 use?

The Dynaco ST-70 / Stereo 70 uses a GZ34 rectifier. Alternatives include 5AR4 (same tube, US name). Swapping rectifier tubes affects sag, compression and the perceived "feel" of the amp at high volume.

How much power does the Dynaco ST-70 / Stereo 70 produce?

The Dynaco ST-70 / Stereo 70 produces approximately 35 W per channel of hi-fi audio power. Era: 1959–1980 (Dynaco era).

Tube chart · Hi-fi amplifier

Tubes for Dynaco ST-70 / Stereo 70

Era: 1959–1980 (Dynaco era)Power: 35 W per channel

The single best-selling stereo tube amplifier of all time — over 350 000 units shipped from 1959. Push-pull EL34 in ultralinear, GZ34 rectifier, simple but exceptionally well-engineered output transformers. The original driver board used the 7199 pentode-triode, but it is NOS-only today; modern conversion boards (VTA, Curcio, Dynakit Parts) replace it with two 12AT7 or 6GH8A in equivalent topology.

Complete tube line-up

Every socket in the ST-70 / Stereo 70, with stock tubes, direct-swap alternatives, and rolling notes. Tube names link to dedicated specification pages.

Voltage amp / phase splitter (modern conversion) × 2
12AT712AT7 / ECC81
Alt:7199 (original, NOS only), 6GH8A, 12AU7 (some boards)
Power tubes (ultralinear push-pull) × 4
EL34
Alt:6CA7, KT77
Rectifier
GZ34GZ34 / 5AR4
Alt:5AR4 (same tube, US name)

Important: bias before you swap

Power tube swaps almost always require rebiasing — running a new quartet of EL34 cold or hot will shorten tube life dramatically and can damage the output transformer. See the biasing guide and the troubleshooting guide before rolling tubes.

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