How to know if a HMV soundbox No. 4 needs to be repaired?

[rasmus.baath]

I've been stalking this great forum since I bought a black HMV 101 on a flea market one month ago (In Lund, Sweden). The mechanics seems to be in great shape but the sound is a bit distorted (which might of course be due to the records being worn out). The machine uses a No 4 soundbox and I've been trying to read up on that still I'm a bit confused. What I haven't figured out is:

1. How do you know when your soundbox is damaged and needs to be repaired (or worst case, replaced)? What can be said from a visual inspection (e.g. the pictures I've attached this post)?

2. Some of the suggested actions when having a bad sounding soundbox seems to be to replace the diaphragm and the gasket. Is it advisable to try to do this yourself if your a happy amateur?

3. The soundbox No 4 seems to have been made in two versions, one of brass and one of pot metal. I've seen mentions of the pot metal version "crumbling" when taken apart (http://forum.talkingmachine.info/viewto ... f=2&t=1745) and I really don't want that to happen How to know what operations are safe when handling a HMV No 4 soundbox?

Any tips or advice are highly appreciated!

Below are some pictures of my HMV 101 and it's No 4 soundbox:

The soundbox

the soundbox

The Soundbox

The soundbox

HMV 101 Black

HMV 101 Black

HMV 101

DSC02077.JPG (99.23 KiB) Viewed 5863 times

/Rasmus

[OrthoFan]

From the photos, I'd say it was due for an overhaul.

First of all, the center of the diaphragm looks damaged. From the back, it looks like it has a small crack, and there's separation of the mica layers visible from the front. That can have a MAJOR impact on overall sound quality.

Along this line, the back rubber gasket or O-ring is due for replacement. It looks hard and there are visible line cracks in the surface. If the gaskets holding the mica in place are original, they are probably shot as well, and should be replaced before trying to play too many records.

I also spotted some fine line cracks running through the front plate, which is made out of pot metal. Not sure if that would cause problems when trying to open the sound box to do the repairs. (I'll let the HMV experts address that.)


OF

[Steve]

The bad news is, my friend, that you most definitely have a pot-metal No. 4 there as Ortho_Fan has already stated.

Whilst I would agree that it most definitely does need a rebuild, I would at the same time contradict myself and advise you not to do it. The front bezzel and back-plate are very prone to breaking apart when removed with any kind of pressure. The gaskets tend to stick to the back-plate and also to the mica (although that in itself hardly matters when you have an already damaged diaphragm) so you will need some pressure to get the thing apart.

The solution? Well, I would suggest you buy another BRASS No. 4 s/box and when you've taken that one part (no problems normally) get your local plating shop to re-chrome the front bezzel. That's the only really satisfactory way to do it. Just in case you didn't already know this: ALL brass No. 4's are either nickel plated (most commonly found) or sometimes gold-plated / lacquered. They were never originally chromium plated.

[rasmus.baath]

Steve and Ortho_Fan, thank you for your advice! Much appreciated! I guess I will have to hang around ebay and see if I can get my hands on a brass No 4. The two soundboxes No4 recently for sale on ebay looks nickel plated to me so maybe I bid on them Then I'll look for my screwdrivers.

Soundbox 1 on Ebay

no4_1.JPG (37.78 KiB) Viewed 5811 times

Soundbox 2 on ebay

no4_2.JPG (35.25 KiB) Viewed 5811 times

The world of mechanic phonographs is really new to me but as a fan of 20s jazz and machine tinkering it's a great experience!

/Rasmus

[Steve]

Yes, they're both nickel plated. Another clue to identifying a pot metal No. 4 compared to the more common brass type is the rubber insulator inside the back-plate flange. You will note that the insulator on your No. 4 (chrome) stands proud of the rim of the flange and over-hangs the edge of it very slightly? The 'standard' No. 4 insulator finishes flush with the edge of the flange and does not project beyond it at all.

[Steve E.]

Rather than start a new thread on this topic, I'll leapfrog onto this one. I too have a No. 4 reproducer which came with an HMV 101. (specifically, an HMV C101G).

After I requested such, I have a kind offer to buy No. 4 replacement gaskets from a collector on this site. However, second guessing myself...as I don't have money to toss around, I want to double check whether I need them. (He may answer the question, too, but I want to speed up the process.)

My No.4 distorts on some 1930s era records, but I know these mica diaphragms naturally have limits. I don't know what to expect from it in terms of quality, so I don't know whether the gaskets have been replaced in the past 80 plus years. Unfortunately, I did not keep the Ebay documentation when I bought the machine two years ago.

If I push on the red rubber on the front of the reproducer, it does have a little give and spring. Would it be hard as rock if it were the original rubber?

I guess I also need to consider the pot metal breakage issue. I see no coloration on mine that would indicate the possibility that mine is the brass variety.

Other than that, it looks to be in good shape. A little of the black wax in the middle of the diaphragm seems to have cracked off.

[rasmus.baath]

Do you have any pictures of your soundbox?

[Steve E.]

I wish my phone camera were better..but this will hopefully give you an idea.

[VintageTechnologies]

Steve, your reproducer sure looks like pot metal to me. I have not worked on that model, but you have to assume there could be difficulty or even a risk trying to take it apart. Pot metal is cursed stuff. New rubber gaskets and flanges would make a noticeable difference in volume and bass response, and there would be somewhat less rattle and blasting if you play very loud or electric records. Now that I have heard the difference, I plan to rebuild all of my reproducers. I tend to play only acoustic records on reproducers with mica diaphragms.

[syncopeter]

I Do not see any cracks, just a bit of paint missing, The mica also looks good. It should be repairable with new rubbers and a new drop of wax on the needle bar. But do not do it your self,