Dynaco Mk. III Monophonic Power Amplifier


The Mark III uses a novel and simple circuit. A pentode voltage amplifier, with parameters adjusted for minimum distortion, is directly coupled to a cathodyne phase inverter. High frequency compensation is employed in a capacitive feedback loop, which corrects the inherent unbalance of this type of phase inverter. The inverter drives the output tubes which are operated with fixed bias. The connection of the output tubes includes a small percentage of screen loading which improves the regulation of the stage and makes it comparatively uncitical of load impedance. The impedance match and bias conditions utilized in the output stage provide minimum distortion operation over a very wide dynamic range. In addition, 20 dB of negative feedback lowers the distortion to an unmeasurable proportion at normal listening levels and to less than 1% IM at 60 watts output.

Phase compensation at both high and low frequencies is incorporated into the circuit arrangement to provide a wide margin of stability and to make construction uncritical. This feature of the design means that there is no tendency toward motorboating or oscillation under and conditions of use.


Power Output: 60 watts continuous(rms).

Intermodulation Distortion: Less than 1% at 60 watts; less than .5% below 50 watts. These figures apply for any conventional combination of test frequencies.


±.5 dB 6 cps to over 60 kc.
±.1 dB 20 cps to 20 kc at any level between 1 mw and 60 watts.

Power Response: 20 cps to 20,000 cps within 1 dB of 60 watts without exceeding 1% harmonic distortion over this range.

Square Wave Response: Essentially undistorted 20 cps to 20,000 cps on loudspeaker load.

Input Impedance: 500,000 ohms.

Sensitivity: 1.6 volts rms input for 60 watts output.

Hum and Noise: Better than 90 dB below rated output.

Damping Factor: 15.

Output Impedances: 4, 8, and 16 ohms (no restrapping required for changing output impedances).

Tubes: KT-88 (2)[early] / 6550 (2)[late], 6AN8, GZ-34.

Size: 9" by 9" by 6-3/4" high.

Weight: 28 pounds.

Designed by:

David Hafler, Ed Laurent

Year Introduced:



$79.95 kit
$99.95 assembled


The classic monoblock tube amplifier. As highly regarded today as it was when it first hit the streets. The target for hundreds of aftermarket modifications and amateur experimentation. Introduced in 1957. Thanks to Ned Carlson from Triode Electronics for the scan of the classic review!

click here to see the 1957 review of the Mk. III in Audio magazine.

This page created and maintained by Greg Dunn.
Copyright © 2000,2001 Greg Dunn