Vox Public Address amplifiers - sockets and plugs
Below, a detail of the back panel of a PA100 from mid 1965. As can be seen, the amp originally had six sockets - 1/4" in diameter - corresponding to the two sets of legends for the impedance settings "0" (common), "8", and "15". Three holes were later enlarged to accommodate jack sockets.
The sockets fitted at factory were evidently Belling Lee L1737s, probably white or grey to judge from the small detail of the PA50 below. L1737 sockets were produced until recently as 2mm connectors - to accept 2mm "banana" or "wander" plugs - current rating 10 amps at 60 volts. In the 1960s, the format will have been 5/64" rather than 2mm.
In spite of the adequate current rating, these sockets and plugs seem a little flimsy, not particularly well suited to the regular plugging in and unplugging of speaker cables on stages. This may to some extent explain why so few early Vox PA amps survive - plugs or sockets failing, taking out the output transformer.
In late 1965 / early 1966 such connectors were phased out, replaced by large Bulgin two-pin connectors and/or simple jack sockets.
Detail from a PA100 from 1965. Three of the original openings have been widened to aceept jack sockets, a new hole added at right.
Detail from a slope-fronted PA50 from later 1965.
Belling Lee L1737 sockets - diameter of the body now 6mm, the closest metric equivalent to the 1/4" diameter of the originals (6.3mm).
Belling L1727As and most modern 2mm plugs requiring a soldered connection will generally accept a good size wire - as in the picture below.
Belling also made stacking connectors to allow two cables to be run from a single socket.
It is important to use plugs with a spring-grip shaft - a particular characteristic of the Belling L1727A. Plugs with straight shafts - the Belling L1727 for instance - will simply fall out at the slightest tug.
Belling Lee supplies
Below, a detail from a more recent Belling Lee catalogue - the L1737 socket and L1727A plugs.
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