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BTH SUPA Remembered

by David Stephenson, February, 2017.
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The BTH SUPA Projector

One of my grammar school friends in the mid-1960s had a father (Mr Gilbert) who worked for AEI Sound Equipment. He used to take charge of the PA equipment for the school, especially the summer fete, and had 'acquired' several ex-SUPA amplifier racks which were obviously a slightly newer version of what is described in your article.

By the mid-1950s, the power amplifiers had been upgraded from what is described in your article, the power outputs being doubled by substituting KT66s (1 pair push-pull for 45W and 2 pairs for 90W) for the earlier Pen44s. The preamplifiers remained unchanged.

In the early 1960s the whole system (3 pull-out 'trays') was progressively replaced by a single tray incorporating pre- and power-amps and power supply, with more 'modern' valves. From memory the valves included EF86 inputs from each projector, ECC83s for interstage amplification and phase splitting, and 1 or 2 pairs of EL34s, with twin GZ34 rectifiers. Voltage stabilisation in the power supply was abandoned.

As an aside, Mr Gilbert also sold my father two B.T-H. / AEI 5-20 (EL34s) power amplifiers and a Leak Varislope Stereo for his HiFi system. I still have them - in working order....

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