If you had posted this a couple of years ago I could have trumped you with a 1938 Cossor (spl??) I had stored in its original teak box, out in the garage (FAR too heavy to lift into the loft!!).
The Cossor originally came from RRE in Malvern, where it probably helped to develop RADAR during WW2; I got it from my employers training centre where they had decided to dispose of it - just after I had given it a thorough service and spruce-up.
The bandwidth went all the way out to 20Khz!!!!
I also had a couple of similar era signal generators from the same source.
Sadly they all "disappeared" while I was out of the country.