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Old 16th Feb 2020, 4:28 pm   #16
Join Date: Jan 2010
Location: North Somerset, UK.
Posts: 1,458
Default Re: 1950's Speaker Connection Plug

Originally Posted by Hartley118 View Post
Rather than the common 4mm plugs, wander plugs are 3mm.

Not sure what caused this handy size to go obsolete.

I was told that use was discouraged, and perhaps actually prohibited, because the plugs fitted the mains voltage selector on some sets.
One common type of mains voltage adjustment used a small 2 pin plug, with the 2 pins connected together. By inserting the plug into different combinations of holes, differing tappings on a transformer or dropper resistance could be selected.
Connecting a speaker to these connections could be most dangerous.

The larger 4mm plugs were I believe also banned for domestic equipment because the plugs fit European mains sockets.
4mm plugs are still used in labs and workshops, but are not allowed on new domestic appliances.
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