The Type F speaker has a 4-pin plug that fits into the speaker socket for my AK Model 55 receiver. At first glance, it looks like a 4-pin pre-octal tube base, but the pin spacing isn't the quite the same.

Often, Type F speakers sold over eBay or at swap meets are missing their plugs. (Who has them all?)

In any case, about a year ago, I was unable to find a reproduction replacement plug from any of the usual sources, so wound up buying a used one.

I wonder if Mr. A. A. Kent decided to use a proprietary, non-standard speaker connector to discourage the use of non-AK speakers?