The 3/16" standard jack - power in - UK Vintage Radio Repair and Restoration Discussion Forum

6SN7WGTB · 20th Apr 2021, 3:05 pm

On my Nombrex 31 RF SG there is a socket on the back which the instructions describe as for external power...

"using a standard 3/16" 2-pole concentric jack plug"

In the absence of a battery (which the external power will disconnect when plugged in) I used a 3.5mm plug to apply external power.

This worked fine bar NOT disconnecting the battery connections - not surprising as it's too small to make the disconnect.

So, I tried to source a 3/16" plug so that I will have the correct disconnect of battery.

A Neutrik 4.4mm is too large, which puzzled me as 3/16" is over 4.75mm and so I would have expected it to be ideal.

Using a hole gauge or drill blank does show the socket to be more like 3.6mm.

Bit baffled. It's a red plastic socket in a zinc-plated surround, clipped in to the case. It's nothing like any sort of 3.5mm socket I've seen. I see no sign that it isn't original, as the slight surface corrosion matches the front aerial sockets.

Does anyone have a suggestion? I'm loath to change it so as not to spoil the originality, and will simply disconnect the battery if I need ext power.

20th Apr 2021, 3:05 pm	#1
6SN7WGTB Hexode Join Date: Apr 2021 Location: Crawley, West Sussex, UK. Posts: 442	The 3/16" standard jack - power in On my Nombrex 31 RF SG there is a socket on the back which the instructions describe as for external power... "using a standard 3/16" 2-pole concentric jack plug" In the absence of a battery (which the external power will disconnect when plugged in) I used a 3.5mm plug to apply external power. This worked fine bar NOT disconnecting the battery connections - not surprising as it's too small to make the disconnect. So, I tried to source a 3/16" plug so that I will have the correct disconnect of battery. A Neutrik 4.4mm is too large, which puzzled me as 3/16" is over 4.75mm and so I would have expected it to be ideal. Using a hole gauge or drill blank does show the socket to be more like 3.6mm. Bit baffled. It's a red plastic socket in a zinc-plated surround, clipped in to the case. It's nothing like any sort of 3.5mm socket I've seen. I see no sign that it isn't original, as the slight surface corrosion matches the front aerial sockets. Does anyone have a suggestion? I'm loath to change it so as not to spoil the originality, and will simply disconnect the battery if I need ext power.