Earthy Ground and Interferance.
Thank you SaintDanBert and Jefro for your follow up reply's.
The links to the symbols are good Thank You as reference but I think missed one or two from back in the 40/50s that is -I on its side referring to plate earth Ie a copper plate buried in the ground, also I recall a spike earth but forget the symbol.
It is good to swap ideas and observations, it makes the world less isolated.
Now if we lived closer we could go to local pub, for a yarn about the old days.
Jefro ref "tube guitar amps" or as we would say "valve guitar amps" those were the days, only last week I fitted a "Humdinger" to the input of a Modern amplifier to cut down mains hum.
I had to use more turns to get the effect as the input was considerably lower impedance than the old Tub/Valve amps, it worked.
For the folk that may not know about Hum Dingers, it is a modification to the input of a amplifier to reduce or eliminate mains born interference.
It consists of a coil of stiff wire one to ten turns of approx 25mm or one inch inserted in the input lead of the amplifier this is then adjusted by turning and twisting the coil while listening for the interference, maybe increasing or decreasing the turns to get the best effect.
The theory is that by inducing into the input an amount of interference in opposite phase to the offending pickup you are able to cancel it out.
It works most times.
Regards to all