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9
Technical Talk
1) The Original Deacy
As already mentioned in DETAILS at the beginning of this manual, the original
amplifier itself dates back to a Mullard circuit that was published when transistors
first became available as a consumer product, and was probably “rescued” from a
car radio, as it is built on a commercial printed circuit board. The amp features the
total amount of four germanium transistors
— two for the preamp and driver stage, and
two for the push-pull output stage.
The cir-
cuit also has an inter-stage driver transformer
(between the driver transistor and the push-
pull pair) and also an output transformer from
the output stage into the speaker.
When connected to a 9 Volt lantern battery the
amp produces a massive 0.45 Watts output.
The amp circuit-board was mounted into a 1960’s contemporary bookshelf HiFi
speaker cabinet, of quite small proportions (England’s bookshelves were not very
big at the time!), and contains a small woofer loudspeaker and a cone tweeter
that is coupled through a capacitor. Due to the speaker technology of the time
(and having been played for many years by Brian) it has a relatively mellow sound
when compared to today’s hi-tech, hi-fidelity speaker systems. As it happens, said
mellowness is actually quite complementary when the original Deacy is used in
conjunction with Brian’s homemade guitar and Treble Booster.
Due to the very low input impedance (12kOhms) of the amp John Deacon sal-
vaged from a pile of rubbish (remember, in all probability it was originally de-
signed for use in a car radio), it is actually not very useable when a guitar is
plugged directly into it. This is because guitar pickups need to see a much higher
impedance in order to do their job properly. Hence the use of Brian’s homemade
Booster pedal was vitally important, not only in terms of tone but also in terms of
the overall compatibility of the signal path.
As also already stated, all the components used in the original Deacy, including
speakers and the batteries used, are no longer in production. It is also worth
reiterating two other facts:
i) The original Deacy had no controls what-so-ever.
&
ii) It was always used in conjunction with Brian’s homemade Treble
Booster — which, to be accurate, actually boosted the upper mid-range
frequencies.
© Richard Gray