I've had several email's about some of my test gear in recent weeks and one item of interest from many was the cable used on my B&K E-200D Signal Generator. I used a premade 50 ohm BNC cable and attached a 2501F connector. So if you need these connectors they can be found numerous places. Search for 2501F, vintage mic connector etc to locate the connector. I prefer when possible to keep my gear original in case I sell the unit for an upgrade and the cost of the connectors is very small. I was able to purchase two for less than $12 including shipping. On is a BNC adapter and I used the other for a 50ohm gator clip style cable. Switchcraft is the manufacture of the connectors I used.
The datasheet is below.