Questions on Exhibition reproducer rebuild

[audioengr]

Should the bar that screws to the center of the mica diaphragm be pushing on the mica when it is fully assembled?

If you make it just touch the mica before putting the back on, this will put the mica under tension because it moves the mica when you compress the back into place.

If the mica diaphragm is not supposed to be under tension, it would seem to me that you want to wait until the back is on and both gaskets are compressed before you check to see that the lever is just touching the mica and then put in the tiny screw.

Also, it is necessary to put wax on both sides or just on the lever side?

[AZ*]

The needle bar should not push or pull the diaphragm when assembled. I always wax both sides.

See step by step instructions here:

https://www.nipperhead.com/old/rep_exhib.htm

You should buy a copy of The Compleat Talking Machine by Reiss which covers most repair and restoration topics.

[audioengr]

The problem with the instructions that you cite is exactly my concern.

When you adjust the lever so that it just touches the diaphragm before installing the second gasket and putting the back on, this puts pressure on the diaphragm when you put the back on. This happens because when you install the back, it compresses the first gasket moving the diaphragm.

If no pressure on the diaphragm is the goal, then the lever should be adjusted to just touch the diaphragm AFTER the second gasket is installed and the back is installed. Only then can you install the tiny screw in the diaphragm. This is how I have been doing it.

[Phonolair]

When I rebuild an Exhibition reproducer I install the diaphragm, both gaskets and the back.
Then I adjust the screws to slowly bring the needle bar arm down to just touch the diaphragm. You don't want to have to push or pull on the diaphragm to install the small center screw.
I then seal with wax on both sides of the small center screw.

Larry Crandell

[Jerry B.]

Excellent suggestions and replies. Thanks!

Jerry B.

[Phono-Phan]

It is amazing how much louder the reproducer is if the needle bar is set correctly and not pushing or pulling on the diaphragm.

[AZ*]

The problem with the instructions that you cite is exactly my concern.

When you adjust the lever so that it just touches the diaphragm before installing the second gasket and putting the back on, this puts pressure on the diaphragm when you put the back on. This happens because when you install the back, it compresses the first gasket moving the diaphragm.

If no pressure on the diaphragm is the goal, then the lever should be adjusted to just touch the diaphragm AFTER the second gasket is installed and the back is installed. Only then can you install the tiny screw in the diaphragm. This is how I have been doing it.

Did you miss the first sentence in my initial reply? I said, "The needle bar should not push or pull the diaphragm when assembled."

I thought that was your question.

[audioengr]

The problem with the instructions that you cite is exactly my concern.

When you adjust the lever so that it just touches the diaphragm before installing the second gasket and putting the back on, this puts pressure on the diaphragm when you put the back on. This happens because when you install the back, it compresses the first gasket moving the diaphragm.

If no pressure on the diaphragm is the goal, then the lever should be adjusted to just touch the diaphragm AFTER the second gasket is installed and the back is installed. Only then can you install the tiny screw in the diaphragm. This is how I have been doing it.

Did you miss the first sentence in my initial reply? I said, "The needle bar should not push or pull the diaphragm when assembled."

I thought that was your question.

I read the instructions that you recommended and these are problematic IMO.

[Inigo]

The trick is that you cannot screw in completely the diaphragm to the needlebar until you've adjusted the backplate. I attach the diaphragm to the needlebar with the small screw loose, without the backplate. But this allows for that small movement when adjusting the backplate. After the backplate is in place and adjusted, you play with the balance springs screws for the final needlebar adjustment. The play in the diaphragm screw allows for these small movements. Once the needlebar is in place, then you can introduce a precision screwdriver through the neck and tighten the diaphragm screw completely. Then you place a little ball of wax on the screw head with the aid of the screwdriver, and then touch it with another heated screwdriver or with the soldering iron also through the neck, molten the wax and seal the tiny screw all around. Then you do the same by the outer face, on the needlebar foot.
Will write later step by step instructions, as I do it, allowing for readjustments. I've found the exhibition a bit difficult due to the balance springs...
EDIT
Infinite adjustments are possible with the balance springs. Provided you adjust for the needlebar foot 'barely touching the diaphragm', this is possible at different pressures of both springs. The ideal would be to do the equilibrium adjustment at the minimum pressure, and then play records, high and low, with different needles, and if there is rattle or buzzing at the loud passages, unscrew again the little diaphragm screw, loose but not detached, and adjust again the balance screws at more pressure on the springs. Then tighten the small screw and try again. This should be done until you find the adjustment that works well with most records. IMHO, one cannot pretend that it sounds well with ALL records and needles. There is an infinite variation on acoustic recordings quality and volume. I've found that if you adjust the springs so tight that there is no rattle or buzzing on the highest passages with loud needles, then the soft records will sound dull, and you loose this marvelous presence and real sound with some soft records. On the other hand, if you adjust so soft that the soft records sound very well, it will buzz on louder records. I feel the best is not to force the machine. You can adjust at an intermediate pressure on the springs so that a soft record with loud needles sounds fine, and that a loud recording sounds also well using softer needles. In the end you will want to play well the louder records, not losing that marvelous sound on good soft recordings. There will be records that sound bad or shrill, and there will be others really life-like. There are simply bad recordings (I've found many Spanish Odeons sound very tubby and unpleasant) and there are good recordings, and another ones that are incredibly good. It depends on many factors, not the
gramophone alone. The horns and diaphragms used are an essential part. Some recording experts mastered their techniques, but in general, there are also many bad recordings, even some overmodulated.
After several trials, once you are happy with the overall performance, then secure the locking nuts at the balance screws (without moving the adjustment) and seal with wax the diaphragm screw.

[audioengr]

Do you think that the dynamics or bass might improve if the lever was bent to be a bit longer in order to put the two springs under less stress? Less of the ends of the screws protruding?

Will this cause the louder recordings to "buzz" or overshoot?