Friend dropped in.....

[Sapper740]

Here is the spare valve case that I have in my collection. I believe from looking at what has been offered for sale the same "physical sized metal box" was used for several different numbered "Case Spare Valves", this example being a number 4A. The internal linings may have differed of which is missing in this example.

By referencing the dimensions shown in the pics below one can see that this case is a little larger than known examples of Thompson magazine case, https://www.milsurps.com/showthread.php?t=77655 (bottom of page), although the height is about the same. As I previously alluded to, it could be that a different spare valve case was used for the Thompson magazine case or there was more than one size of Thompson mag box.

That's the spare valve case for the R 106 HRO radio set which was a militarized commercial radio mainly made for the U.S. Military but also supplied to the British.