I've posted an answer on the UK forum. Only a physical difference between tubes. 226 etc. were globe shaped tubes. When they converted over to "ST" shape first digit was dropped. Electrically tubes are the same.
Norm
:I'm currently working on this 20's Victor and on the tube sockets it says 226 227 280 171A etc and some of the tubes are 226's they test low when using the tube tester set to 26 and some of them are 26's what's the diff and are they exact replacments? The 227 is a 27 and the 171A's are 45's also the 280 has an 80 in it's place. Do you just dis-regard the first number? Brian