The Armstrong A10 Mk 2

In 1957 the original A10 power amplifier and control unit were replaced by the A10 Mk2 versions. The Mk2 was Ted Rule's first ‘Hi Fi’ audio amplier design for Armstrong.

The above picture shows an A10 Mk 2 power amplifier. As with the unit it replaced, this was a monophonic amplifier. As well as some detailed alterations to the circuit, the appearance was modernised to a ‘bronze crackle’ finish.

The Mk 2 was broadly similar to the Mk 1 version. The main change was employing EL34 output valves, and a new output transformer. The basic performance of the A 10 Mk 2 was as given in the table below.

Specifications for A10 Mk 2 Power Amplifier
Rated Output	12 Watts (Output transformer tappings for 3, 7·5, and 15 Ohms)
Frequency Response	15Hz - 30kHz ±1dB	Distortion	<0·1%
Input sensitivity	80 mV for full rated output	Output Valves	EL34 ultra-linear’s
Noise	-80dB	Feeback	28dB

The changes slightly increased the availiable power from 10 to 12 Watts (for 0·1% THD) and increased the sensitivity.

The above image shows a view of the inside of the A10 Mk 2 chassis and enables they layout of the components to be seen.

The control unit was also re-styled and updated to match the Mk 2. The photo above is a monochrome publicity photo of the Mk 2's control unit. The difference between the appearances of the Mk 1 and control units can be seen more clearly in the colour photos shown below.

The specifications for the Mk 2 control unit were: Inputs for radio (70 mV), tape (18 mV), mic (18 mV), gramophone (18 - 230 mV adjustable, with a selection of four equalisation curves). Six position low-pass filter. Treble, Bass, and Volume controls. THD 0·05% or less at 1 kHz/180mV. Hum and Noise less than -60dB. Rumble filter.

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