Mystery so-called 3/16" plug/socket - UK Vintage Radio Repair and Restoration Discussion Forum

6SN7WGTB · 31st Jan 2022, 11:27 am

I have a Nombrex RF SG and it is powered by a PP4 battery.

There is also a socket on the back which is quoted as suitable for a "standard 3/16" 2-pole concentric jack plug" in order to apply power in, and it has switching action to disconnect the battery.

However, it certainly is not 3/16"! It measures 3.8mm with a hole gauge.

It all looks highly original.

I tried a 4.4mm Neutrik plug but (a) it is too large (in spite of 3/16" being >4.75mm) and (b) way too long.

A 3.5mm modern plug enters, appears the right length, but is too small to actuate the switching. Given how loose it is, and the fact that it does not work, it doesn't seem as though Nombrex moved to 3.5mm but failed to update the literature.

Picture attached - ignore the fact that the plugs are stereo - this was just what I had to hand.

Anyone know what this mystery socket/plug arrangement is?

Vintage Engr · 31st Jan 2022, 11:47 am

I used to have one of these, way back in1963. It looks the same as mine was, & that used an original miniature two-pole jack plug.
The Radiospares ones fitted. The modern 3.5mm do not fit. Also the actual distances & size/shape of centre pin on the old type was slightly different.

David.

barrymagrec · 31st Jan 2022, 11:50 am

I have one of these Nombrex units which I inherited from an Uncle thirty years ago and have never used

The socket is black, unlike yours but the dimensions appear similar. I measured a modern (RS) 3.5mm plug at 3.4 and it fails to operate the switch as you say but I found an older plug which measures 3.5 and while still loose ish it operates the switch and seems fairly secure. I`m not sure of the origin of this plug but the name Igranic seems to ring a bell.

Possibly not very useful from your point of view though.

ronbryan · 31st Jan 2022, 12:05 pm

There is this thread on the Forum that illustrates a standard Bulgin 3/16" mono jack plug. It has a ball end, so maybe would be gripped better by your panel socket.

https://www.vintage-radio.net/forum/...ad.php?t=66094

Ron

6SN7WGTB · 31st Jan 2022, 1:46 pm

Quote:

Originally Posted by ronbryan

There is this thread on the Forum that illustrates a standard Bulgin 3/16" mono jack plug. It has a ball end, so maybe would be gripped better by your panel socket.

https://www.vintage-radio.net/forum/...ad.php?t=66094

Ron

Taken a look at that thread, but the plug shown circled is again too long and if anywhere near 3/16" too large a diameter.

The apparent depth of the one on the Nombrex is about 15mm - very much akin to the 3.5mm plug length.

A solution, assuming I retain the socket for originality, may be simply to bodge a larger 'ball end' using solder on a 3.5mm mono plug.

Thanks to all for the various suggestions.

31st Jan 2022, 11:27 am	#1
6SN7WGTB Hexode Join Date: Apr 2021 Location: Crawley, West Sussex, UK. Posts: 444	Mystery so-called 3/16" plug/socket I have a Nombrex RF SG and it is powered by a PP4 battery. There is also a socket on the back which is quoted as suitable for a "standard 3/16" 2-pole concentric jack plug" in order to apply power in, and it has switching action to disconnect the battery. However, it certainly is not 3/16"! It measures 3.8mm with a hole gauge. It all looks highly original. I tried a 4.4mm Neutrik plug but (a) it is too large (in spite of 3/16" being >4.75mm) and (b) way too long. A 3.5mm modern plug enters, appears the right length, but is too small to actuate the switching. Given how loose it is, and the fact that it does not work, it doesn't seem as though Nombrex moved to 3.5mm but failed to update the literature. Picture attached - ignore the fact that the plugs are stereo - this was just what I had to hand. Anyone know what this mystery socket/plug arrangement is? Attached Thumbnails

31st Jan 2022, 11:47 am	#2
Vintage Engr Heptode Join Date: Jan 2008 Location: Shrewsbury, Shropshire, UK. Posts: 843	Re: Mystery so-called 3/16" plug/socket I used to have one of these, way back in1963. It looks the same as mine was, & that used an original miniature two-pole jack plug. The Radiospares ones fitted. The modern 3.5mm do not fit. Also the actual distances & size/shape of centre pin on the old type was slightly different. David.

31st Jan 2022, 11:50 am	#3
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,561	Re: Mystery so-called 3/16" plug/socket I have one of these Nombrex units which I inherited from an Uncle thirty years ago and have never used The socket is black, unlike yours but the dimensions appear similar. I measured a modern (RS) 3.5mm plug at 3.4 and it fails to operate the switch as you say but I found an older plug which measures 3.5 and while still loose ish it operates the switch and seems fairly secure. I`m not sure of the origin of this plug but the name Igranic seems to ring a bell. Possibly not very useful from your point of view though.

31st Jan 2022, 12:05 pm	#4
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Mystery so-called 3/16" plug/socket There is this thread on the Forum that illustrates a standard Bulgin 3/16" mono jack plug. It has a ball end, so maybe would be gripped better by your panel socket. https://www.vintage-radio.net/forum/...ad.php?t=66094 Ron