The Pye Mozart was first seen at the 1957 London Audio Fair. It was, for
its day, remarkably small, and was one of the first British amplifiers
to utilised the new single-ended Mullard EL34 output pentode which gave
considerable peak power and low distortion from a tall and thin glass
envelope that saved on chassis space. Another space-saving feature was
the use of special highly efficient grain-orientated steel transformers
with a claimed efficiency of over 90%.
The amplifier produced 9 watts RMS with a distortion figure of only 0.3% and a printed circuit was used for most of the wiring. The single EL84 output stage received a distributed load via the cathode, which was fed from a winding on the output transformer (which was also as a loudspeaker winding). In this way the voltage on the screen grid of the EL34 was kept rock-steady.
The Mozart also featured a novel feature for the time, dubbed 'Dialomatic' pickup compensation. This consisted of two controls mounted on the back of the chassis, the first being the lower half of a potential divider, its own value being a maximum of 100 K ohms when in the maximum position. The second control made up the upper half of the divider network and also had a maximum value of 100 K. The pickup was wired across both controls in series before being sent to the amplifier. By altering both controls it was possible to compensate for all of the well-known pickups of the day. A table of recommended settings was supplied for most British, Continental and American manufacturers. Another interesting feature was a control for adjusting damping factor, from 15 to infinity.
Several versions of the Mozart were produced:
The basic HF10 with no case - £23 2s
The HF10M with a lightweight metal cover (pictured here) - £24 13s
The 'Lowboy' which was fitted into a walnut veneer cabinet with space
for a turntable - £33 12s (matching legs an extra £2 2s)
An export model, the HF10EM, was also produced for use with 117 volts,
50/60 c/s.
A stereo version, the Mozart HFS20 was released in 1959.
Today's value (2005) is around £250 for a good, clean, fully operational example.
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