"Lost"?? Perhaps a friend or relative absconded with them?
That rectifier is a bit of mystery.
The vendor told me he believes it is a Klangfilm. However, there are no markings of any kind on the tube to help identify it. On the glass pinch, the number "2.5" is written. But this probably suggests that it has a 2.5 amp heater as I often see the heater currrent written on the pinch of these old 4-volt rectifiers. So again, it is a bit of a mystery.
That said, we know that Klangfilm did manufacture their own vacuum tubes in the early days, but later tubes were sourced from Telefunken. Comparing the construction of Klangfilm and Telefunken rectifiers I see on eBay, they look very similar, if not identical. Moreover, the Klangfilm tubes usually carry Telefunken date codes! So I am inclined to believe that the vast majority of the Klangfilm tubes I see on eBay were in fact manufactured by Telefunken.
So it may well be wishful thinking on my part, but it is certainly possible that this is a "real" Klangfilm KL76303, which is equivalent to the Telefunken RGN2504. The construction of this tube "exudes" quality to my eyes. Morever, I have never seen another tube anything like it. So if it isn't a Klangfilm, then I have absolutely no idea who made it. It is a mystery.