Vox VBM1 owner manual Technical Talk, Original Deacy

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.

© Richard Gray

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.

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ii)It was always used in conjunction with Brian’s homemade Treble Booster — w hich, to be accurate, actually boosted the upper mid-range frequencies.

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