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BUSH MB60

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Front View [31K]

  • Released June 1957
  • LW plus MW superhet
  • 5 Valves (DK96, two DF96,
    DAF96 plus DL96).
  • Mains or battery.
  • Original cost £15 17s 6d
    plus purchase tax.
NOTES
The first incarnation of this classic cabinet design.

The set uses the standard range of battery valves. However it is unusual in having an extra I.F. stage, hence the presence of two DF96's. This should improve both sensitivity and selectivity and presumably the extra gain this gave also allowed the designers to include -ve feedback in the audio stages to improve sound quality.
Mains PSU Circuit [7K]
The extra valve meant that the the valve heaters could not be series-connected since standard batteries for the job were 7.5V or 1.5V yet 9V would have been necessary. They therefore had to be connected in parallel. The total filament current of 300mA meant that, unlike many other mains/battery sets, it was not practical to run the heaters via a dropper resitor from the rectified-and-smoothed H.T. (the generated heat would be considerable and the H.T. smoothing cap would need to be large). Thus the mains transfromer has an additional winding to generate the low "1.5" volt filament supply. It is however difficult to accurately obtain such low voltages and so a forward-biased metal rectifier MR2 (which presumably has a forward voltage of around 1.4V) is used to regulate the supply. Note the huge (by 1950's standards) smoothing capacitors that the supply requires.

Mains connector, showing mains/battery switches [7K]The mains on-off switch is part of the tone control potentiometer and standard controls of this type would include one or two switches. However we appear to need three (battery H.T. and L.T., plus one mains). This problem was resolved by adding two extra switches so as to feed the battery's H.T.+ via the mains on/off switch. This is not as risky as it first sounds since the mains/battery switching is operated by the insertion/removal of the mains input connector, the arrangement illustrated opposite.
SERVICE DATA There is a copy of the Trader service sheet #1403 on CD#1.
CURRENT STATE
Physically sound, just needing a light clean. However half of one of one of the mains connector pins is missing and I dont have a suitable mains lead either.

From the quality of the circuit design I have high expections for the performance of this set.
WHERE FOUND Bought locally via an advert in the B.V.W.S. magazine for £15.
SEE ALSO TR82 - Later all-transistor version
VTR103- Updated TR82 including V.H.F. waveband.

Rear View [33K]Long WaveMedium Wave208 Selector


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J.Evans 2003
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Last updated
5th May 2003