Stereophonic Amplifier Mk.VII (Mk.7)

Stereophonic Amplifier Mk. VII

This was a very interesting amplifier misleadingly named the 'Stereophonic' but was actually mono.

It incorporated two amplifiers and an active crossover built on one chassis.

Without a doubt, this amplifier was ahead of its time, having a single-ended triode covering mid/treble frequencies and push-pull PX4 triodes for feeding the ' woofer'.

 According to users, gives the highest quality of any reproducer so far produced. This high quality is to be expected when the particular points of the design are considered. The large reduction of intermodulation distortion and Doppler effect is achieved by completely separate amplifier channels for the high and low frequencies, terminating in separate speakers.

 The latter may be separated by any convenient distance to prevent pressure wave modulation and it is unnecessary to restrict the bass to prevent marring treble response. In each case, the speaker is damped by a minimum of 12 times at audible frequencies to prevent speaker resonance, and the crossover is very fast, approximately 28 dB for the first octave. A control is provided to vary the power applied to the treble speaker, to compensate for its efficiency compared with the bass speaker, and a frequency record reveals the absence of dip or rise in output at crossover frequencies.

The treble control gives a 20 dB lift or 14 dB cut from 3,000 cycles and compensates for long-playing records and various American and English recording characteristics.
The small improvements in the latest model amplifier result in reproduction that is extremely good and capable of pleasing all tastes. Chassis complete with valves Price 36- gns
Wireless World Nov 1950, Page 71.

Here you find 22 models, 18 with images and 1 with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.
All listed radios etc. from Vortexion Ltd.; Wimbledon