HMV no. 4 soundbox rebuild

[CharliePhono]

Wishing to draw upon the collective expertise of the forum regarding my first rebuild of an HMV no. 4 soundbox. It's a brass-bodied one of the second iteration (logo on back plate) and is on a recently acquired 101 portable. With the new mounting flange and gaskets installed, I have to admit I was very pleased with the sound. I cleaned and very lightly lubricated the pivot points on the needle bar. I was enjoying a pile of clean early 20s acoustic records and reveling in the reproduction. I decided the last disc I would play for the night would be a Victor Scroll (very clean, ca. 1927) and found the reproduction almost shockingly "bright." I think every coyote in my area heard those highs. It was frankly bordering on unpleasant. Before I go monkeying around further with the soundbox, I wanted to inquire if this issue lies in needing to possibly adjust the pivot points? They are well centered with no horizontal play, but I wondered if perhaps, even for lateral movement, they could potentially be too loose? I should mention that the unit is airtight and, I believe, well sealed. For

Thanks, as always, to all for your advice and insights.

[CarlosV]

Charlie, I would start by checking if the problem is not on the record itself, after all if you played several before and their sound was good then it could be a fault in the record. You can do that by playing the record on another machine. But if you want to optimize the soundbox, the only way I know is trial-and-error. I start by tightening the pivots to the extent that they can barely move, then play a selected record, and start to slightly loosen the screws, repeat the same record, and keep repeating the process until I get a reproduction that sounds good. The process is simple, the nr 4 is easy to adjust, but it will take your time and patience.

Does your soundbox have a flexible rubber on the arm attachment? hardened rubber connections usually mar the reproduction.

[CharliePhono]

Charlie, I would start by checking if the problem is not on the record itself, after all if you played several before and their sound was good then it could be a fault in the record. You can do that by playing the record on another machine. But if you want to optimize the soundbox, the only way I know is trial-and-error. I start by tightening the pivots to the extent that they can barely move, then play a selected record, and start to slightly loosen the screws, repeat the same record, and keep repeating the process until I get a reproduction that sounds good. The process is simple, the nr 4 is easy to adjust, but it will take your time and patience.

Does your soundbox have a flexible rubber on the arm attachment? hardened rubber connections usually mar the reproduction.

Great suggestion, Carlos, and thank you. I will try that. Yes, there is a new rubber connector on the soundbox.

[MicaMonster]

The needle bar tension should be adjusted when the unit is a part. It should be able to stay in position just barely able to hold up its own weight before falling inwardly or outwardly when the reproducer is positioned horizontal. The rubber gaskets for the diaphragm should not be rock hard. Reproduction gaskets are nothing more than solid pieces of rubber. The original gaskets were made out of soft rubber. Hard rubber gaskets are going to give you too much treble. I use medical grade tubular silicone as an ideal gasket replacement for the #4. The results are astounding.

[epigramophone]

The needle bar tension should be adjusted when the unit is a part. It should be able to stay in position just barely able to hold up its own weight before falling inwardly or outwardly when the reproducer is positioned horizontal. The rubber gaskets for the diaphragm should not be rock hard. Reproduction gaskets are nothing more than solid pieces of rubber. The original gaskets were made out of soft rubber. Hard rubber gaskets are going to give you too much treble. I use medical grade tubular silicone as an ideal gasket replacement for the #4. The results are astounding.

Some UK collectors also report good results from replacing the original one piece gasket with separate tubing. One gentleman adds that using a thinner diaphragm than the original improves matters even further.

[CharliePhono]

The needle bar tension should be adjusted when the unit is a part. It should be able to stay in position just barely able to hold up its own weight before falling inwardly or outwardly when the reproducer is positioned horizontal. The rubber gaskets for the diaphragm should not be rock hard. Reproduction gaskets are nothing more than solid pieces of rubber. The original gaskets were made out of soft rubber. Hard rubber gaskets are going to give you too much treble. I use medical grade tubular silicone as an ideal gasket replacement for the #4. The results are astounding.

Thank you very much, MM, for that directive. I've always been a bit unsure about the proper tension. Thus far, I have been mostly pleased with the soundbox, save for what I feel is excess treble. Other than that, the reproduction on acoustics has been astounding, though far too strident on electrics for my tastes. I have purchased red tubular silicone gasket material from a fellow in France and am awaiting a new mounting flange from eBayer, EMGExpert. What is sold on eBay as a "rebuild kit" for this soundbox I have found to be inadequate, poorly fitting and needing too much in the way of cobbling for a "make-do" fit/rebuild. If this No. 4 sounds as good as it does at this point, I am very anxious to hear it with the silicone gaskets and a proper-fitting mounting flange. When apart the second time, I will follow your directive on tensioning the needle bar with the soundbox apart. Thanks again. Much appreciate.

[CharliePhono]

The needle bar tension should be adjusted when the unit is a part. It should be able to stay in position just barely able to hold up its own weight before falling inwardly or outwardly when the reproducer is positioned horizontal. The rubber gaskets for the diaphragm should not be rock hard. Reproduction gaskets are nothing more than solid pieces of rubber. The original gaskets were made out of soft rubber. Hard rubber gaskets are going to give you too much treble. I use medical grade tubular silicone as an ideal gasket replacement for the #4. The results are astounding.

Some UK collectors also report good results from replacing the original one piece gasket with separate tubing. One gentleman adds that using a thinner diaphragm than the original improves matters even further.

The one-piece gasket on this No. 4 was literally rock hard when I got it. I have seen the one-piece gasketing for sale somewhere on ebay.co.uk, but can't recall just where at this time.

I don't recommend the kits on eBay which are proffered as "rebuild kits" for both the Victrola No. 2 and the HMV No. 4. The gaskets are ill fitting and as well one has to wrap the mounting flange with electrician's tape to effect a snug fit. While one can "make do" with this stuff, it's not my idea of a proper rebuild.

[CharliePhono]

[/quote]

Some UK collectors also report good results from replacing the original one piece gasket with separate tubing. One gentleman adds that using a thinner diaphragm than the original improves matters even further.[/quote]

Oh yes, I have also procured a new mica diaphragm, also ordered from across the pond via eBay. When the soundbox was apart the first time, I noticed too much flaking around the edges of the diaphragm, which made me a tad uncomfortable (perfectionist here). That said, on the second go-round, it will get the new silicone tubing gasketing, a proper-fitting mounting flange (of the proper durometric consistency) as well as the new diaphragm. Should be a marvel at that point!

[shoshani]

The needle bar tension should be adjusted when the unit is a part. It should be able to stay in position just barely able to hold up its own weight before falling inwardly or outwardly when the reproducer is positioned horizontal. The rubber gaskets for the diaphragm should not be rock hard. Reproduction gaskets are nothing more than solid pieces of rubber. The original gaskets were made out of soft rubber. Hard rubber gaskets are going to give you too much treble. I use medical grade tubular silicone as an ideal gasket replacement for the #4. The results are astounding.

I can vouch for the medical grade tubular silicone. MicaMonster rebuilt my HMV No 4 and it sounds amazing.