HMV No:4 Soundbox question.

[Phono48]

Are the brass backed ones entirely solid brass I wonder ?

Yes, unless the fronts have been swapped for pot-metal ones, I've come across one or two that have. Beware, soundboxes are a veritable minefield!

Barry

[JerryVan]

However, once opened it seems to have a very thin 'coating' of brass and the rest of it appears to be pot-metal ?

I thought it would be solid brass ?

What are your thought please ?

The very thin coating is paint.

[leels1]

Also be careful with the screws holding the back plates on, I’ve found they can sometimes be really tight and almost welded in. When you try and unscrew them they snap as they’re very thin brass. It’s really annoying to drill them out the brass front bezel.
Some penetrating oil does help to free them up!

Interesting. Now you mention it, I did notice that the screws were made of brass and therefore a little 'soft'.

Penetrating oil !!! I wish I had thought of that ! I bet that would have been very good to loosen the back.

Great advice, thanks leels1

I don’t think that’d help get a swollen pot meal back of though. I’ve seen them swell that much, that it splits the front part (usually at the point where one of the screws is).
If that does happen though, you can then at least get the back off, file it down so it fits again, but you’d have to braize the front together at the split and tap a new screw hole.

[leels1]

When making the adjustments to the needle bar pivot, this is a good guide: https://www.nipperhead.com/old/vic4sb.htm It's identical to the HMV #4 sound box.

Here are the basic/easy steps explained to me several years ago.

No 4 Sound Box Pivot.jpg

Keep in mind the collar is not threaded and moves in and out. If it seems frozen, apply some penetrating oil to the area. To test for side play, try moving the needle bar in the direction of the pivot screws. If you feel a sideways movement, repeat the above steps, since side play can cause buzzing or blasting. The needle bar should only move in the direction required to track the record's groove.

HTH,
OrthoFan

Those end screws can also freeze in so when you try and unscrew them they just snap off. The penetrating oil is a good idea, or try and unscrew the nut and slide the pivot bar out with the screw in and then heat it a bit to lose. They can rust and almost weld themselves in!

[shoshani]

A good guide to which back a No.4 soundbox has is the rubber isolator.
If it is flush fitting you have brass. If it protrudes you have pot metal.

I'm not sure whether the image attachments will be quoted as well, but they offer a very good visual guide as well. The lettering on the back of a brass backed No 4 will be thinner in body and crisper in appearance, whereas the lettering on the pot metal back will be wider/thicker in the letters and not quite as clearly defined.

And then there's the One True Giveaway for a brass backed No 4: having the wording on the front inside, to be read through the mica diaphragm!

[poodling around]

However, once opened it seems to have a very thin 'coating' of brass and the rest of it appears to be pot-metal ?

I thought it would be solid brass ?

What are your thought please ?

The very thin coating is paint.

Very good observation !

Thanks JerryVan.

[poodling around]

Also be careful with the screws holding the back plates on, I’ve found they can sometimes be really tight and almost welded in. When you try and unscrew them they snap as they’re very thin brass. It’s really annoying to drill them out the brass front bezel.
Some penetrating oil does help to free them up!

Interesting. Now you mention it, I did notice that the screws were made of brass and therefore a little 'soft'.

Penetrating oil !!! I wish I had thought of that ! I bet that would have been very good to loosen the back.

Great advice, thanks leels1

I don’t think that’d help get a swollen pot meal back of though. I’ve seen them swell that much, that it splits the front part (usually at the point where one of the screws is).
If that does happen though, you can then at least get the back off, file it down so it fits again, but you’d have to braize the front together at the split and tap a new screw hole.

Good advice and much appreciated.

Thanks leels1

[leels1]

Thought you might like to see this modified HMV No 4 soundbox with a resin back.

I had several front sections knocking about so decided to make a silicone mould from a brass back and then make a resin copy.

It was a bit of a pain to get the resin to get into all the nooks and crannies so several didn’t quite work out.

The diaphragm is a NOS one that’s quite thin, but sounds ok. I need to make a new one in the EMG style and see if that sounds any better.

The grommet screw holes cast ok, but eventually the silicone broke and they do need filling and drilling if a proper rubber connector is used. I’m using a 25mm grommet from eBay that fits the back and tone arm perfectly for a 5 type fitting so I’ll probably leave as it is.

Anyway, here’s a link to it playing on an HMV 152. https://youtu.be/PTJd3N9S6_s?si=xwvBEWQSajvoDH0U

I’d welcome any improvement suggestions!

[Inigo]

Nice experiment! And from your own impressions and judgement "in the flesh"... how does it sound when compared with the original 5B of this machine, the mica HMV no4, or the Meltrope...?
I was tempted myself to modify a surplus no4 but with a handmade diaphragm. But I'm involved in the Exhibition nowadays, and there's also the thing that I love the looks of those mica soundboxes, and when I install a metallic diaphragm it loses part of its charm... Even using transparent glass I've tried, noticing that you lose that lovely brownish colour of the mica. A nickel soundbox with transparent glass diaphragm has a nasty look of an old medical contraption...

[leels1]

Nice experiment! And from your own impressions and judgement "in the flesh"... how does it sound when compared with the original 5B of this machine, the mica HMV no4, or the Meltrope...?
I was tempted myself to modify a surplus no4 but with a handmade diaphragm. But I'm involved in the Exhibition nowadays, and there's also the thing that I love the looks of those mica soundboxes, and when I install a metallic diaphragm it loses part of its charm... Even using transparent glass I've tried, noticing that you lose that lovely brownish colour of the mica. A nickel soundbox with transparent glass diaphragm has a nasty look of an old medical contraption...

It might need some tweaking, but it sounds pretty good. I still like the Meltrope probably the best as it has a more bassy sound but this OK. I don't think the Mica 4 sounds that great, especially on newer records. This home made one sounds closest to a 5a/ 5b but i've always thought they sound a bit "thin".