Telephone Jack ID?

[Goodizzy]

Good afternoon,

I'm hoping someone can identify this jack type that was used to measure voltages in a Leak TL/25 amp. It was used with an 8-position rotary switch.

Thanks!

[G6Tanuki]

It looks very much like the old "B-gauge" GPO jacks [also known as a '316' ] that were used in the days of manual telephone-exchanges.

http://www.designacable.com/componen...-jack-pro.html would mate. Note that these "tip-ring-sleeve" jacks are subtly different to the current generation of stereo 1/4-inch plugs - in particular the shape of the 'nipple' on the tip. You can't satisfactorily mate a stereo 1/4-inch and a 316.

[Goodizzy]

Thank you very much for that answer. I have been wondering about it since I got the amp.

As the 316 appears to be an outdated jack/plug, what would be a modern or cheaper NOS equivalent for test purposes?

[Nicklyons2]

It isn't outdated by any means, it is still an industry standard in the UK at least - if you want plugs I can send you some if you pay the postage.

[Goodizzy]

Oh, so sorry, I didn't realise. I am not familiar with it here in the US, but my knowledge of this type of stuff isn't very great.

Thank you for your kind offer regarding these. I may take you up on that!

[Nymrod121]

You'll see a typical B-gauge 'double-ender' being used for back-to-back testing in my photos in this post:

http://vintage-radio.net/forum/showp...14&postcount=2

The other term you'll see is PO316. The original design are machined brass with a plastic sleeve held in place by a tiny little brass screw.

Another common brand is Neutrik.

Even second-hand, both types tend to go for eye-watering prices on internet auction sites

Best wishes
Guy

[Goodizzy]

I will keep an eye out for more jacks on those terrible internet sites, haha. I am interested in using them in test porta throughout a very small all-valve mixing desk.

[emeritus]

Here's an extract from the Dec 1974 RS catalogue showing both types. From a quick look on their current on-line catalogue, the type B plug with that stock code is shown as "discontinued". They do list two connectors that seem to be compatible :

"through hole" plug

http://uk.rs-online.com/web/p/jack-t...ctors/8784850/

and "Phone plug"

http://uk.rs-online.com/web/p/jack-t...ctors/8768656/

but both are shown as "out of stock".

When VAT (Value Added Tax) was introduced in the UK a couple of years later, no VAT was initially payable on the Type B plug as it was classified as "industrial" rather than "consumer".

[bobsterkent]

yes it fits the 316 plug and one of those would have been used as the battery point for the engineer to plug in his test lamp or headlamp

[julie_m]

The "B-tyoe" connectors are what the BBC used to use for balanced analogue audio. They are similar to a 6.3 "A-type" stereo headphone plug, but the middle and end contacts are progressively narrower compared to the earth contact, and the retaining groove is deeper.

The brass-barrelled "B-type" jacks as per the picture would accept a standard 6.3 "A-type" headphone plug, but there were plastic-bodied jacks designed for "B-type" plugs into which an "A-type" plug would not fit because the holes in the separating cheeks between the contact springs were too narrow. In any case, the misuse of "A-type" plugs in "B-type" sockets was discouraged, for fear of permanently bending the spring contacts out of position and unable to mate properly with a "B-type" plug in future; but I never had any problems in practice, using the brass-barrel "B-type" jacks just for "A-type" headphone plugs.

[Nicklyons2]

Personally I would never plug a normal 1/4" (6.3mm) jack plug into the 'B' sockets it will cause excessive wear and will very likely sprain the socket contacts.

I believe Newark - element 14 a US subsidiary of UK Farnells www.newark.com
stocks the Neutrik NP3TB-B which is the same as the Post-Office jack you require
it is Newarks's part No. 90F2061.

Just a caution make sure it is the 1/4" (6.3) mm version you require; there are 2 smaller versions of the same shape: 4.4mm 'bantam' and a 5.5mm aircraft version. Just check by seeing if a 'normal' jack will fit in the hole but don't push it fully home.

[Goodizzy]

Fantastic information, I appreciate it. This Leak TL/25 is an industrial variant with EMI/REDD markings, so I'm guessing the BBC use for balanced analogue audio is the likely connection. I'm unsure about battery connection for headphones?

The markings around the associated rotary are HT, V1, V2a, V2b, etc. This seems to indicate a voltmeter test jack of some sort to me.

I'm not sure it will be financially feasible to obtain enough of these jacks and plugs to do multiple line amp test ports. I'm guessing the cheaper domestic US version of old may still suffice. I do have an affinity for the analogue voltmeters and these telephone leaf jacks, switches and such.

[peter_sol]

The BBC would have been the only ones to have used such a Jack for such purposes
The original use of the B type jack plug was on manual switchboards UK and US

[Goodizzy]

Thanks for that information. I suppose EMI must have been doing something similar. in conclusion, to beat into my daft head once more- both the UK and US used the same type of B-gauge jack for telephone systems?

[peter_sol]

https://www.google.co.uk/search?q=us...7rrbiuwmkIM%3A

Yes you can clearly see the plugs with a smaller tip and slight bulge of the ring. bottom right hand corner of the picture.

[Goodizzy]

Very interesting! Many more thanks for all this information- I find this stuff fascinating. Is there any documentation of the BBC use of this format for test purposes. BBC Engineering monographs maybe?

[Nicklyons2]

The use of the type B jack for balanced audio extended to everyone I've ever encountered in professional audio in the UK for patch fields and also some portable amps and test equipment and large static recorders. Now, of course, it has been largely replaced on all equipment requiring analogue inputs by the 'XLR'. Note for interconnection to type 'B' TRS jack T=L, R=R & S=X=screen=gnd.

[Goodizzy]

Thanks- I may still pursue this for testing purposes. I suppose an avometer is in store? I have a Radioshack analogue multimeter that I use primarily. 20,000ohm/volt- cheap but does the job. I wonder if I couldn't build a test lead using another set of standardised lead plugs and a B-gauge at the other end, to use with this chintzy multimeter.

I will have to research further I suppose. I'm not familiar with the telephone broadcast industry, though it is intriguing.

[radiotechnician]

Here is a telephone gear jack field with that type shown. The essential part is they are meant to be mounted on an insulated panel. On a old switchboard the tip and the ring are the voice/signal line circuit while the brass ferrule (sleeve) is the supervisory system. I bought two of these recently on E-bay.

As the son of a Bell Telephone worker, these are in the blood, and will be put to use in my shop.

[Nymrod121]

Here are some pics of a broadcast transmission-specific 'B' gauge jackfield (I'm told it may have been recovered from Morborne after the mast collapsed due to fire damage a few years back).
Other than the somewhat incongrous tie-wraps that are most definitely not down to an Avenue House wireman, the wiring/lacing quality is nothing less than a work of art.
Truly, a thing of beauty is a joy forever
Cheers
Guy