[BC] RCA phono plugs - How far back?

[Tom]

Well, sorta -

The WE type 310 is/was a TRS, and dates from the manual plugboard 
era. The "standard" 1/4" TRS (and the related TS) started as 
HEADPHONE plugs/jacks; and they do NOT fit an original type 310 jack 
- at least, not without springing (and damaging) the contacts.

The 310 "looks" metric, but it predates the current love affair with 
the metric system... it's a unique Bell System legacy. BTW - the dual 
TS plugs were also a WE design.

http://www.westek.com/Cords-c-263.html

The 310 patch cords are on page 2...

the ADC patch panels mate with these plugs naturally...

https://www-wsp.adc.com/ecom/catalog/hierDisplay.do?NODE=OND3081



RichardBJohnson at comcast.net wrote:
>The TRS (Tip-Ring-Sleeve) phone-jack is as old as the telephone
>switchboard and Western electric. There were two sizes, the
>early ones that had a 1/4 in dia. maximum size and a late-model
>one that had some "!^$_!@#%" metric size before their use was
>superseded by electronic switching. I never saw them used
>anywhere in radio except for earphone jacks, microphones,
>and musical instruments, even the junky ones on consumer
>equipment were used to plug in earphones or "crystal"
>microphones.