I am about to start looking for some 12B4A that should be lying around and do some final soldering to my 12B4A darling. The 1626 Darling is, at the moment in a safe place (down in our basement storage room).
As I had a feeling of seeing the end of the tunnel light I started a thread on the Swedish electronics forum. EF, and took this photo of the 1626 compared to 12B4A and 2A3 and also included a Russian 807 and a VT25.
Now I wonder, could the VT-25 (Y10) be a candidate for Darling? It has the correct shape, is a triode, should be rated 3/4W but has directly heated filaments.
On the photo, from left to right: 2A3, 1626, 12B4A, VT-25, 807.