I DO NOT SUPPLY
Prompted by a forum posting on No. 15 soundbox refurbishment by a friend and fellow collector I have created this page based upon his posting and with his permission.
The Columbia No 15 Soundbox Refurbishment
Let's start with a drawing of The No 15 Soundbox to be aware of just what's going on
The No.15 is one of the easiest soundboxes to overhaul. Take the front and back off, and remove the front rubber gasket.
Undo the two nuts at the base of the stylus bar, and holding the soundbox over a tray, slowly undo the screws that are inside the nuts. the stylus bar will then come loose, but watch out for the six tiny ball bearings in each side. (hence the tray!). Remove the needlebar and diaphragm through the soundboxe aperture. Remove the gasket. Note the position of the join is opposite to the one from the front.
Dig the bearings out with a wooden cocktail stick, and leave them to soak in a small dish of petrol, thinners, or alcohol. Meanwhile, clean out the sockets of the stylus bar with a small, stiff brush dipped in whatever you are using to wash the ball bearings in. Clean the pointed ends of the two bearing screws.
If the diaphragm is damaged it will need replacing. ( See links panel for suitable replacement ) Separate by removing the screw that connects the diaphragm and needlebar. On early examples this may be a nut.
You are now ready to re-assemble. Put a blob of grease in the sockets of the stylus bar, just to hold the tiny ball bearings in place. Replace the ball bearings. Rather than trying to arrange them into a perfect circle, it's easier to drop six in to the socket, and push them into place with a cocktail stick. When one side is filled,turn it over and fill the other side.
Cut a new piece of rubber gasket, making sure that the it's a good tight circle, with no gaps, and place it in the bottom of the soundbox body, with the join at the top or bottom of the soundbox.
Where a new diaphragm is being fitted follow the relevant parts relating to the No 4. for fixing and waxing, placing the diaphragm into its aperture, aligning the holes in the diaphragm and needlebar. Do ensure the diaphragm is not touching the sides of the soundbox. This may mean some further rea djustment of the needlebar position.
Place the needlebar, with or without diaphragm, depending upon whether this is being replaced, back between its pivots. Now adjust the two pivot screws so that the diaphragm, if it isn't being replaced, is sitting centrally, and not touching the rim of the soundbox casing. Tighten the nuts, but make sure that the stylus bar is still swinging freely, this is most important. Do not tighten the nuts up at this stage. Fine adjustment will be done later.
Cut the other new gasket, making the join at the opposite side of the soundbox to the join in the other gasket. Place that in, and replace the back of the soundbox.
Now for the "fine tuning". This can be done in 2 ways.
1. Looking from the front, slacken the left hand nut, just enough allow the screw in it to be turned. Pick a record that's not too worn, and play it. Whilst it's playing, carefully and slowly tighten the screw until any distortion or rattling is eliminated, and then stop. It's very important that the screw is not over-tightened, or the stylus bar will not be free to move and will wreck records very quickly. When you are satisfied with the sound, hold the screw in position firmly whilst you tighten up the nut. (You need three hands)
2. With the diaphragm and needlebar assembly in position check for lateral movement in the needlebar between the 2 pivots, If there is no movement slacken off one of the screws until lateral movement is obtained. Maintaing the needlebar centrally between the two supports tighten one or both of the pivot scews. The aim is to take up the lateral movement to the point at which it just disappears whilst also mainting a central, balanced position. When that point is reached lock off each nut without changing the position of the pivot screw. (The illustrations reagarding the HMV No 4 should help here.) Test on a record and adjust further if necessary.
Note method 1 will give a better indication of the sound quality but requires a steady hand. Method 2 does not allow you to hear any sound differences but is less dependent up the dexterity required in adjusting the pivots while a record is playing.
Replace the front of the soundbox, and job done.
Click thumbnails for larger images
The Replacement Diaphragm.
New diaphragms are available. Click the link left. The particular one required has a diameter of 51mm and is reference 1029 005115 in the catalogue. They are not as thin as the originals but are a very satisfactory alternative. One has been used in the example shown on this page.
See HMV No. 21 Insulator should it be necessary to replace the red rubber insulator that allows insulation from the tonearm should this be necessary