Increasingly HMV gramophones from the 1930s are turning up with 5A or 5B sound-boxes that have suffered damage due to the alloys used in their construction. These alloys , known as “Mazac” or “Potmetal” tend to swell with age and damage occurs, especially around the locating pin where the sound-box is attached to the tone-arm. (See picture) The swelling of the back-plate can even cause the front ring of the sound-box to split. Probably all 5A/5B sound-boxes will suffer in this way eventually.
A replacement back for these sound-boxes has just been developed. It is made from high quality aluminium and the connection fits directly onto the tone-arm without the need of the rubber insert. I have tested the back-piece and find that the results are excellent and with the additional advantage of the sound-box being lighter, applying less pressure to the record surface. It has been suggested to me that this might be a disadvantage, but I have not found that to be so.
The development of this new back-plate offers a new lease of life to these, otherwise excellent, sound-boxes.
I HAVE RECENTLY RECEIVED NEW SUPPLIES OF THESE EXCELLENT BACK-PLATES FREALLY WELL ENGINEERED AND WILL FIT PERFECTLY TO REPAIR AND ENHANCE No.5A AND 5B SOUND-BOXES. I HAVE ALSO A FEW BACKS FOR HMV No.4 SOUND-BOXES.
Price including p&p £35