[Mike. Watterson]

Originally Posted by G6Tanuki

I always thought that the first B7G valves were the 9001/9002/9003

http://www.r-type.org/exhib/aab0161.htm
http://www.r-type.org/exhib/aaa0254.htm
http://www.r-type.org/exhib/aaa0253.htm

which were essentially Acorns re-engineered to avoid the seal-cracking-and-loss-of-vacuum issues that beset the Acorns.

The Acorn was a bad idea, both to make and in service, so logical some re-engineered. However B7G battery valves were demonstrated in 1940 with very many radios in 1941.
The re-engineered Acorns were a couple of years later, 1943.
The B7G valves only imported to UK during WWII for military and covert applications. Two radios (a TRF, Sweetheart and Superhet) were built in the UK during WWII. No domestic sets used the B7G in UK till 1946.
https://www.radiomuseum.org/r/simons...heart_311.html

This is like a military version of a US 1941 Personal Radio.
https://www.radiomuseum.org/r/mil_gb_op_3_type_301.html
Except the US Models only had MW (Broadcast).
UK models using B7G battery valves adding LW (or SW for export) appeared in 1948.

I don't know when the first mains sets in UK using B7G valves appeared. Possibly ITT-KB and EMI (HMV) would have been first.