The Armstrong A Series

The ‘A’ series covers the decade from 1954 to 1963. Previous to these units, Armstrong mainly produced valve radio and radiogram chassis. In modern terms, the ‘A’ series were the first true ‘Hi Fi’ amplifier units that Armstrong made. During this period Armstrong continued to make valve radiogram chassis, etc, but this was a declining part of the business, and these ceased to be made by the mid 1960's. The 200 range replaced the ‘A’ series in 1963/4.

The units were:

A10 Mono power amp (1954 - 57) A10 Mono control unit (1954 - 57)
A10 Mk 2 Mono power amp (1957 - 61) A10 Mk 2 Mono control unit (1957 - 62)
A6 Mono power amp (1959 - 61) PCU21 Stereo control unit (1959 - 62)
A20 Stereo power amp (1961 - 63) PCU25 Stereo control unit (1961 - 63)
PCU27 Stereo control unit (1959 - 63)
All dates approx.

A6cu.jpeg - 40Kb

The above image shows a pair of A6 mono power amplifiers with a PCU21 stereo control unit. The PCU21 could also be used with a single A6 as a mono amplifier system. The A6/PCU21 were later models than the A10 and its control unit. They were introduced as a low-cost way for people to acquire stereo amplification or to upgrade an existing mono amplifier system to stereo.

Specifications for A6 Power Amplifier
Rated Output 6 Watts (Output transformer tappings for 3, 8, and 15 Ohms)
Frequency Response 15Hz - 35kHz ±2dB Distortion <0·5%
Input sensitivity 700 mV for full rated output Output Valves ECL82’s
Noise -70dB Feeback 14dB

The PCU21 had inputs for Tape (500mV), Radio (180mV), and Gram (10/28/180 mV). As a fairly basic “no frills” unit it did not have any filters, and only RIAA disc equalisation was provided. From left to right, the control provided were:
The A6/PCU21 were designed by Ted Rule. Ted joined the company in the early 1950's, and worked initially as a tester. When George Tillett (who designed the A10 Mk1 and its control unit) left in the mid-1950's he was promoted to the job of audio and radio designer. He was then responsible for the electronics of all their later amplifier and tuner designs up to and including the 600 range.

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