From Bakelite to CAD

By Martin Herrick, 2025

I manufacture custom guitar and bass pickups using the multi-coil technology and I am also interested in the early electric reproducers for disc recordings. I have disassembled and restored close to 150 of these dating to around 1925-1950 starting with the pioneering horseshoe form magnet types, up to the moving coil era pickups of postwar Britain.
Keith Harrison who has some excellent pages on this site introduced me to the Adrian Sykes page and showed me his video of an Electrograph, I knew I needed one and it took me more than a year to find one and get the chance to examine it myself. The design is very simple and like most patent drawings there are minor differences in the Sykes patent to the actual device. I wanted to find out if it was possible to recreate this 1930's transducer in a small batch production with modern materials.
I used one of my bass multi-coils for the design. My off-the-shelf coil had double the resistance of the one on the Sykes original and it had already been wax saturated, the Sykes original coil was quite tall and quite thin. Arguably, the best shape for a coil (at least on a guitar) is short and fat to ensure superior sound reproduction characteristics.
The original Electrograph coil is similar to around 30% of the gramophone pickups of the 1930's that I have personally encountered in that it has an unsaturated coil which doesn't give the best reproduction due to the coil winds being subject to air gaps that can eventually lead to microphonics or failure.
I built a simple mock-up of the Electrograph mechanism from workshop scraps of brass, aluminium, phenolic resin sheet and steel and the reproduction quality was encouraging. I asked my girlfriend Gosia Dredzik to recreate the Sykes Electrograph body design with a CAD file to print in 3D from PLA (polylactic acid), to use as a housing for a new set of internal components that I had designed around the bass guitar multicoil bobbin and as close to the Sykes original dimensions as was possible to keep to the spirit of things.
This design went through a few versions until we had a candidate with much thicker walls than the original body shell as it would not be produced in Bakelite but a modern thermo-set polymer. Shrinkage rates were worked out and the master was sized to allow shrinkage of 0.4 mm on the horizontal carriage seating ring diameter to ensure a good fit in the subsequent castings.
The copy Electrograph shown in the pictures is a polyurethane casting made from a mould that was cast from a highly cleaned up PLA 3d print that has been added to with a filler material similar to a car body shop material , that had some milling done to it and all the hole locations marked out and was then prepared and finished with a spatter aerosol finish to give the best possible results and a professional looking surface finish in the subsequent copies.
The production cover shells require much post-cast finishing and like the Sykes, the steel work screws to the top of the cover with the extension of the coil outer pole piece. There is a second, or inner pole piece, as on the Sykes to allow precise adjustment of the air gap between the coil pole piece and the metal reed that attaches to the rear of the stylus bar via a wire link. I found that pure nickel wire was the best type to use for the connection.
I intend to produce these in a limited number for other cylinder machine enthusiasts as I feel that electrical reproduction reveals much greater detail than the mechanical equivalent. on these period recordings. I'm planning to produce the electromagnetic top works ONLY as finding a large box of original Edison Diamond "B" weighted sections and stylus bars is unlikely.

The original Electrograph is here seen on the left, Martin Herrick's modern version on the right, and its contents in the middle.

Left to right: the original Electrograph and Martin Herrick's new reproducer.

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