An engineer colleague has managed to produce a few more of the backplates that fit the HMV No.5A or 5B and No.4 sound-boxes. More and more of the originals are suffering from pot-metal decay and develop cracks , especially around the locating pin but also more generally. The pot-metal alloy swells with age and this means that the backs are now often impossible to remove, the swelling can even cause the front ring of the sound-box to split where the small brass bolts are.
These replacement backs are a really excellent way of re-juvinating the very good HMV 5A and 5B sound-boxes from the 1930s and the No.4 sound-boxes from the 1920s. They fit perfectly and have a simplified back fitting for the tone-arm. They are also much lighter than the originals and therefore reduce the pressure onto the record and produce less drag as the needle traverses the record.
The downside is that the new back-plates are expensive to make in both material and man-hours so the price is now £40 plus p&p. At the moment I have only four No.4 and one No.5 back-plates