Dumb Question of the Day - Rebuilding Reproducers

[CDBPDX]

Rebuilding mica diaphragm reproducers always includes adding a dab of wax to the tiny screw that secures the needle bar to the diaphragm. It always seemed logical to me, but I realized I really didn't know why. Is it simply to help prevent the screw from coming loose, or is there another reason?

Thanks! Cliff

[Lucius1958]

It's also to make sure that the connection is airtight.

Bill

[gramophone78]

Cliff, most reproducers have the wax on both sides of the diaphragm. As Bill has stated, to create a air tight seal and also to stop any unrelated vibration between the connection.... .

[Henry]

When I "revised" the rebuild of my Exhibition, I made sure to apply wax to front and back of diaphragm screw. I believe that it makes a significant improvement in the sound, for the reasons stated by Bill and gramophone78.

The professional rebuild I was unhappy with, thus my revision, which consisted of careful adjustment of the needle bar contact with the diaphragm (just ever so barely touching, using a leaf of cigarette paper as a feeler gauge). On the Exhibition, needle bar contact is adjusted by the two screws at the bottom of the sound box. I also added a large felt washer (from an assortment sold by Horror Fright) between the back flange and the body of the sound box to ensure an air-tight seal. The front gaskets as supplied by the rebuilder are perfect, IOW very compliant, and the new back flange is completely satisfactory. The diaphragm is original AFAIK.

Some time back there was a discussion here of the different kinds of beeswax. According to one of our members who is a beekeeper, different colors of wax come from different parts of the hive; he felt that the brown variety of wax was the best. I happened to have some brown on hand, so that's what I used. If anybody's interested, you could probably find that thread using the search feature; sorry I don't have the reference to hand.

[De Soto Frank]

Ok, I'm having a "dense" day... is the beeswax applied after the needle-bar is clamped to the diaphragm, or is a bit of beeswax applied to the center of the diaphragm first, not unlike tinning surfaces before joining them by soldering ?

[Henry]

Frank, I applied the wax after all adjustments were made and the tiny screw was in place; it screws into the needle bar from behind (i.e., back surface of the diaphragm, through the tiny hole in the center of the diaphragm). You have to work with your screwdriver through the throat opening. Original Victor instructions also mention a paper washer under the screw head, but not having any I omitted it and used just the wax, front and back.

Applying the wax is a little tricky. Victor supplied a tool for the purpose: pictures show a tapered rod, resembling nothing so much as an awl with a little hook on the end, mounted in a wooden handle. The tip of the rod is heated in your ever-present bench-top Bunsen burner flame (ha!), and you are to pick up a drop of wax with this heated tool and deposit the drop onto the tip of the needle bar (front of diaphragm), then take up another drop of wax and apply to the screw head (back of diaphragm), once again working through the sound box throat for the latter operation. I used a scribe tool as a substitute for the Victor tool. Others have applied a tiny ball of solid wax to the appropriate spots and then melted the wax with a heated metal tool. I suppose that you could apply heat to the end of the needle bar, but I would be afraid of affecting the temper of the metal by this method.

[Cody K]

Henry's method of first making the attachment to the diaphragm works for me. What I like to do with the wax (for the back side) is flatten it into an appropriately-sized disc, press it very lightly onto the top of the tiny screw, and then melt it on with a very small screwdriver that's been heated over the stove. For the front, I like to roll the wax between thumb and forefingers into a little stick-shape, and wrap it around the needle bar, then apply the hot screwdriver. Doing it this way tends to leave a nice, round blob of wax on either side, with clean, regular edges.

[Henry]

I was a bit sloppy with my wax application and maybe used more than I needed to, resulting in a larger deposit than I had envisioned. However, the sonic results are pretty impressive, and I'm reasoning that a larger amount of wax somehow strengthens the diaphragm vibrations. Anyhow, I wouldn't change anything with this sound box!

[phonojim]

I always make sure that the foot of the Exhibition needle bar is flat against the diaphragm before inserting the screw, because sometimes they are slightly bent or twisted. I use beeswax and heat the bar with a soldering iron. There is very little mass to heat and the wax will melt very quickly.
I've also noticed that the Victors #2 and #4 only have wax applied to the rear (inside) of the diaphragm; I have not seen any of them with wax applied to the outside of the diaphragm.

Jim

[JerryVan]

You really should heat the needle bar to melt the wax, as Jim does. Simply melting wax over a cold needle bar will cause the wax to not adhere to the bar. It's similar to making a "cold joint" when soldering, (where you should also heat the item to be soldered and not the solder itself). The amount of heat required will be far from anything that will affect the metal, as suggested in an above post.

I usually place a small chip of wax next to the bar. I then gently heat the bar using a small soldering iron, making sure the wax chip is in contact. As soon as the wax melts and flows, you're done.