The Talking Machine Forum — For All Antique Phonographs & Recordings

In the course of rebuilding Victor exhibition reproducers/sound boxes, I have always wondered what guidelines those who do this might use to expedite the process. Specifically, in addition to adjusting the front and rear adjusting screws (A and B in the attached diagram) so that the needle arm just touches the diaphragm, how much pressure do you place on the springs while doing this? Those arm springs are notoriously stiff. The Victor instructions that I have seen apparently avoid this aspect of adjustment, referring only to the positioning of the needle arm relative to the diaphragm with a phrase such as “when the screws are properly adjusted”.
I am hoping for answers along the line of “only adjust the springs as tightly as is necessary to remove any free play between needle assembly and fulcrums”, or perhaps “adjust screws so that there is no contact looseness between the needle assembly and the fulcrums, then increase the pressure on the arm springs by screwing in the arm spring screws one quarter turn (insert your version here) more”.

This question comes from knowing that the needle arm must not push or pull on the diaphragm, but that various pressures on the springs achieving that goal will have various impacts on the ability of the needle arm to move in compliance with the vibrations in the record groove. Some balance must be reached between the record blasting and the record sounding “muddy” with loss of sensitivity. I am looking for a “rule of thumb” here based on empirical experience which will achieve a good sounding reproducer that does not blast but which optimizes good frequency response.

I would assume any answer might also apply to Victor No. 2 or No. 4 reproducers and the like. Looking to achieve the best “first approximation” with the least effort here.

So, any rebuilders out there who might like to weight in on this? Please feel free to comment on the efficacy of sharpening fulcrums (knife edges) or other fine tuning techniques.

Thanks,

Don

Thanks for exposing this problem so clearly and masterly. I have the same problem, and what is said to do is to try the slightest pressure on the springs. Then test, and if buzzing or blasting, turn both screws the same little amount (like an eighth of a turn) and test again. Do this until there is no blasting with a good strong early acoustic opera record and a loud tone needle.
This is the theory.
In my experience, I get satisfied until one day, an unsuspected record blasts. Then I turn a bit more both screws.
But I feel like you ; this procedure looks like it will diminish the sensitivity of the diaphragm...
I'm tempted to try softer springs, as an experiment... Not yet tried....

Inigo wrote: Mon Mar 01, 2021 12:08 pm Thanks for exposing this problem so clearly and masterly. I have the same problem, and what is said to do is to try the slightest pressure on the springs. Then test, and if buzzing or blasting, turn both screws the same little amount (like an eighth of a turn) and test again. Do this until there is no blasting with a good strong early acoustic opera record and a loud tone needle.
This is the theory.
In my experience, I get satisfied until one day, an unsuspected record blasts. Then I turn a bit more both screws.
But I feel like you ; this procedure looks like it will diminish the sensitivity of the diaphragm...
I'm tempted to try softer springs, as an experiment... Not yet tried....

I tried to thin the metal down on the springs to make them softer or more compliant. I couldn’t notice much difference but that might be down to poor mica. I hope you give it ago and report back.

I've done several modifications to the exhibition in these two years, reported elsewhere in this forum. Finally, the exhibition I used for experiments was reverted almost to its original configuration. Almost, because I did retain three modifications : a thin glass diaphragm, relaxed gasket pressure on the diaphragm edge (loosening the backplate) and a tracking corrector elbow.
But I'm planning to continue, using one of them for converting into an emg type, metal (handmade) diaphragm and a change in the springs and the fulcrum plate suspension. My error has always been trying to improve the performance of the soundbox in the same gramophone (the hmv tabletop style iii with that internal short conical horn) and this is a major drawback. Next experiments had to be done on the big gramophone with reentrant horn, or on the hmv127 at least (long exponential horn). But I doubt I'll get better sound than with a well tuned 5a soundbox.... Nevertheless, the conversion into an emg type is still something to try.

It sounds like you are deeply into the heart of restoration theory. I think you will likely be very pleased with the outcome, particularly since you are referencing the marvellous EMG machines. Trial and error - and many cycles of do, redo, do again, etc. I know there is a limit to what can be achieved and I would really like to shorten the process of adjusting the springs. Thanks very much for your input!
Don

Yes, yes. I'm most interested in improving the design, or better said, tuning. I'm marveled at the way small modifications in adjustments here and there can improve the sound. I've thoroughly studied the Bible (Percy Wilson's book) and I'm always tinkering with soundboxes. I feel I've learned the physics of this design and how all components work. These later two years it's the Exhibition who arrived to my desk. Never had one before, but the latest machine (a tabletop hmv grand size, two spring old style motor, a French version of the Victrola VI) came with its Exhibition. It is an old model with round needle hole. Soon after, I acquired two more from forum colleagues, and these have triangular needle holes. I've been tinkering with them three all this time, and yet I'm learning about them.... Time will speak... Undoubtedly, the presence of the balance springs introduce more variables in the mechanism, and its more complex than the latter models no4 (the simplest one) and no 5a/b. Yet I'm on the Exhibition and it will take time to experiment with it and arrive to a satisfactory solution.... Fascinating!