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.

A10Mk2.jpeg - 29Kb

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.

A10Mk2base.jpeg - 34Kb

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.

A10Mk2cu - 40Kb

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.

mk1mk2cus.jpeg - 37Kb

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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