I DO NOT SUPPLY
As with many other gramophone components gaskets for the No 4 soundbox seem to experiencing a price hike, no doubt as a result of the increased demand interest in gramophones is generating coupled with a limited supply. Faced with this and an idle hour I started to give the matter some thought. The photos below document my solution to the problem and essentially use an A4 size sheet of 2mm thick rubber and the circle cutting gadget known as the Circlescribe*. Faced with a typical price of £10.50 plus postage for a No 4 gasket my DIY solution will provide 6 gasket sets for what cost me less than £5.
The original gasket for the No.4 soundbox was a single unit with a slot on the inner circumference to take the mica diaphragm. My solution uses 2 separate gaskets and works well but please note. The original with the slot ensured that the edge of the diaphragm did not contact the inside of the soundbox aperture into which it sits. As this protection is not afforded when using 2 separate gaskets extra care needs to be taken to ensure contact between the edge of the diaphragm and the inside of the soundbox aperture is not made. This holds true for any soundbox that uses 2 gaskets.
Note also that the rubber requires supporting during the cut. To do this I used masking tape however the inaccurate cut shown in the left gasket of photo 3 led me to use and extra layer on subsequent gaskets running at 90 degrees to the original layer. This improved the cut but occasionally the rotational movement of the Circlescribe collects the tape causing it to roll up up. Currently I additionally lubricate the blade with a little light oil. This also helps avoid distortion to the rubber during the cut.
* The device for cutting the gaskets is called "Circlescribe" and was intended for the card making fraternity. I say was because I don't think it's available currently although some remaining stock maybe still kicking around as well as secondhand examples from ebay.
HMV No. 4 Gaskets
Click thumbnails for larger images