The  M-60 is a complete 60 watt power amplifier which offers the highest possible fidelity, at low cost and in a compact arrangement. It uses a circuit of outstanding performance characteristics, along with top quality parts, including the A-431 output transformer - the finest available. The measured specifications show that the this is an amplifier of unequalled performance, and its listening quality is also unrivalled by any regardless of price.

The design features of your amplifier which contribute to its superior listening quality do not show up in the usual steady-state laboratory specifications. For example, the amplifier does not exhibit bounce and flutter when pulsed because of its wide margin of stability. The M-60, unlike other amplifiers, has been designed to provide its specified performance on a loudspeaker load, not just a resistive load as in the laboratory. In particular, the connection of a loudspeaker does not distort the high frequency square wave performance. In addition, the power handling capabilities are maintained over the entire audio band without the sharp rise in distortion which characterizes most amplifiers at the low and high frequencies.

The M-60 uses a unique 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 uncritical 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 voltage feedback lowers the distortion to an unmeasurable proportion at normal listening levels and to less than 1% 1M 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 to make construction uncritical. This feature of the design means that there is no tendency toward motorboating or oscillation under any conditions of use. 

 Bias monitoring located on the front panel

makes changing tubes easy, without the need of a DVM.

M-60 Mono Amplifier


Power Output: 60 watts continuous,140 watts peak.

IM Distortion: Less than 1% at 60 watts; less than .5% at 50 watts.

Frequency Response: +/-.5db 6Hz~60,000Hz; +/-.1db 20~20,000Hz at any level between 1mW and 60 watts

Power Response: 20~20,000Hz within 1db of 60 watts without exceeding 1% HD over this range.

Sensitivity: 1.6 volts RMS for 60 watts

S/N Ratio: better than 95dB

Damping factor: 15

Output Impedance: 4,8 and 16 ohms

Tubes 6550 (2), 6AN8, GZ-34

Size: 7.3 X 17 X 8

Weight: 32 pounds

SP-1B Stereo Preamplifier

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