Sony Antenna plug

[MickM]

Hi;
my Sony TV-415 arrived and I got it working.
Just a bad main power Electrolytic cap.

Unfortunately the external antenna socket takes a weird plug.
It is very slightly bigger than a 3.5mm headphone plug.
Does anyone know what this is called?

I have an external digital tuner box with an F connector for the RF out.
I soldered an F connector to a RCA mini plug, for the TV.
You have to lever it up, and hold it there, to get it to work.

There is no room in the set to install an internal F connector.
So I have to find the correct plug, or adapter.

Thanks

Mick M