no. 12 battery for field telephones

[Dave Moll]

As these batteries are for telephones, I trust that this is the appropriate place to post.

Having been for some time the owner of a pair of Telephone Set "F" field telephones, I would like to replace the battery lash-ups that I currently have (using "D" cells) with reproductions of the authentic cells.

As luck would have it, I am now in possession of three original cells, in quite reasonable external condidtion (and one even has sufficient charge in it to draw 2mA with my AVO).

As can be seen from the first picture, I have now dissassembled one and scanned its case (the resolution here is reduced to make the file small enough to upload - if anyone wants a higher-resolution version let me know by PM). When printed out on standard card it looks quite presentable, though I probably need to acquire some thicker card to provide something a little more rigid - I would then go over the white edges of the card with a suitably-coloured felt-tip pen. Rigidity, however, could be provided by making a suitably-sized battery holder to go inside - something I have not yet done.

As for the actual cell inside, I am quite pleased to discover that suitably-sized cells are available off the shelf in a handy four-pack labelled "996".

The area in which I am currently seeking advice is whether anyone can suggest how I can source the screw terminals. I have included as the second picture the terminals from the disassembled battery, but I would like to be able to attach the terminals to the internal holder so that they poke through the cardboard cover, so something like the +ve terminal shown (the short one) is probably what I am looking for as the -ve one could be difficult to attach.

I will keep folks posted on any progress.

[Station X]

Dave.

I'd be happy to turn you up some plausible imitations of the terminals if you can email me a dimensioned drawing or snail mail me a pattern. Don't expect an express service though.

Is it just the terminal posts you require, or do you need terminal nuts as well?

[Dave Moll]

Actually, it's primarily the nuts (both the ring to fasten the terminal to the holder and the knurled nut) that I need, as the terminal post of the +ve terminal is simply a brass bolt:
diameter of threaded section = 3mm
length of threaded section = 10mm
diameter of head (not critical) = 6mm
depth of head (not critical) = 2mm

ring:
diameter = 8mm
depth = 1.5mm

knurled nut:
depth (including knurled section) = 5mm
body diameter = 8mm
diameter of knurled section = 10mm
depth of knurled section = 1.5mm

[mickjjo]

Would these be suitable? :-

http://www.6v6.co.uk/CandyPress/scri...?idproduct=218

Regards, Mick.

[Dave Moll]

Although not identical, they would certainly serve the purpose, but I would prefer without the nickel plating, which wouldn't look quite right.

I could always use these and change them later if non-plated versions turned up - unless it's possible to remove nickel plating!

[Station X]

Dave.

Any idea what the thread on the "bolt", actually a setscrew, is? At 3mm diameter it could be 5BA (47.85 TPI), 1/8" Whitworth (40 TPI) or 4-40 UNC (40 TPI).

Can you identify it by trying nuts of known spec on it or by counting the number of Threads Per Inch (TPI)?

Are the "rings" totally round or do they have a couple of flats on them for a spanner?

[jim_beacon]

for telephone use, my money would be on 5BA, then 1/8" Whit. Definatly not a UNC (I don't thik UNC / UNF became common in the UK until the late 60's).

Jim.

[Dave Moll]

I don't know what I'm doing wrong, but counting the threads on 0.3" worth of bolt (and it is a bolt by the way, including slotted head), I make it 10 turns, so the pitch would be 10 / 0.3 = 33 TPI ... somewhat coarser than any of the figures given above. On the other hand, I'm not too concerned about the pitch if I have a set of parts all of the same pitch.

Incidentally, if the picture I gave is displayed/printed actual size, it should be fairly close to real-life size, as the picture was created by placing the items on the platen of my scanner. This can presumably be checked by comparing the dimensions with those quoted.

The "rings" are totally cylindrical with no detectable flats on them, nor are they slotted like those in the old-fashioned 13A plug terminals. I would imagine that the ring would be lightly gripped while tightening the bolt from inside. It seems that the main thing stopping it from working loose was the outer coating of wax on the battery case.

The -ve terminal is totally different, with a long non-threaded post that was soldered directly to the zinc casing of the cell.

My intention is to make a holder to go within the cardboard case enabling cells to be inserted or removed without the use of a soldering iron.

[Station X]

Setscrews are threaded over their entire length ie right up to the head, whereas bolts have an unthreaded section under the head. I think you need setscrews with slotted heads.

I'll check my thread data and see if I can identify any threads about 3mm diameter with 33 TPI. As you say though it might be preferable to use new screws and make the rings and terminals to fit.

Leave it with me.

[Dave Moll]

I apologise for my (now corrected) ignorance! I had never appreciated this distinction between bolts and setscrews - I've always called both of them "bolts". I' always glad to learn new information.

The distinction I was trying to make was with binding posts. My understanding is that this term means a ring-shaped body with threaded sections issuing from it in both directions - or am I using this term incorrectly as well?

[Station X]

I can't identify any threads around 33 TPI with a diameter of 3mm.

The nearest I can get to it is 6-32 UNC (3.505mm dia x 32 TPI), or 5/32" Whit (3.63mm dia x 32 TPI). Could it possibly be either of these? Whitworth threads have existed since the year dot, but UNC was introduced during WW2 as a common US/UK standard.

I don't think you're likely to find a 5/32" Whit thread to try your teminals and rings on, but 6-32 screws are found in PCs, as can be seen from this Maplin page:-

http://www.maplin.co.uk/searchtempla...06-32%20%20UNC

[Dave Moll]

I will do a bit of experimenting when I get back from Wootton Bassett - as I shall be away until then.

[Colin]

Hi Dave,

Are these any good? They're 4BA thread and seem to be pretty much an exact match in terms of size.

I bought a small number about 18 months ago from a seller called walfram.w on eBay. (email address is - christopher@hearn350.fsnet.co.uk ).

He may have some left, or be able to source some more. If you're really struggling you're welcome to a dozen or so of the ones I have.

good luck
Colin

http://pics.ebaystatic.com/aw/pics/spacer.gif

[Dave Moll]

Thanks for that lead. I will check it out.

I managed to get some (albeit a little smaller) last Saturday in Sale which may do for the time being if I have (or can find) the other bits to make terminals, but if I get stuck, I may get back to you.

[Station X]

The spec for these batteries shows that the thread is 4BA.

[batterymaker1]

I'm doing a dummying together of this battery. Reminds me of a miniature Number 6 cell!

Looks like a D cell, complete with holder, is going to fit inside nicely.

Bill

[Dave Moll]

Further to my musing here about replacing the original cell in a no. 12 battery with one of the four from a "996" lantern battery (perhaps it could be called a "249" cell ), I have now cleaned up the terminals shown in the first post of this thread and soldered them to a new cell (see pic. 1) to give a totally authentic-looking no. 12 battery (see pic. 2 - apologies about the quality as I forgot to zoom in and the auto-focus saw too much background)