The DR-20 tone cabinet

This was one of the first of the Hammond tone cabinets and its design is from a totally different era . The cabinet, which looks as though it would convert into a Victorian drinks cabinet, appears to break all the conventions of acoustic design.

The amplifier sits on a shelf at the bottom behind the grille but otherwise the bottom of the cabinet is open. The cabinet also has the "Venetian Blind" slots in the side to let some sound out. The two 12 inch drive units are mounted on another shelf just below the top and point upwards. Despite being a disaster from the viewpoint of good acoustic design it somehow manages to work producing an acceptable sound although it doesn't go too loud. I also used to have a UK made Boosey & Hawkes tone cabinet which was a double version of this model with two amplifiers and four 12 inch drive units in the one cabinet. It was designed for use in churches.

The amplifier uses two pairs of 2A3 triode valves and is good for about 20 watts output.

The 2A3 is a highly desirable valve much beloved by hi-fi enthusiasts who want to build Class A triode amplifiers. This valve is unusual in needing a 2.5 volt heater supply in place of the modern 6.3 volt supply.

The speaker drive units are these beautiful Jensen 12 inch field coil units. They don't have conventional magnets instead they use electromagnets which are powered from the amplifier's power supply. A very sweet tone completely different to that of modern speakers.

It is difficult to find service information on this amplifier so I've drawn up a simplified circuit which can be downloaded below

Downloads <click on the logo to download>

Circuit Schematic for the amplifer - PENDING

A modified schematic for using the amplifier as part of a hi-fi system - PENDING
• Copyright 2009, 2010
Stan Curtis the hi-fi guru - Hammond DR-20 tone cabinet -