Those clever chaps at GEC-Osram made some of the most memorable and sought after valves made by any manufacturer, they chose valve base styles that were not used by anyone else at the time and envelope shapes which were not at the time used by anyone else so why should their valve numbering system be the same as anyone elses?
Anyhow, I digress for here is a handy little table that will allow you to classify the kinky GEC from the vari-mu GEC - I hope you will find it useful: -
|GU||Gas filled rectifier|
|GT||Gas filled triode|
|H||High imp. triode|
|L||Low imp. signal triode|
|MU||Ind. heated rectifier|
The letter identifier or letter identifier sequence is followed by a sequentially allocated number which is the development number for a particular valve type eg; KT66 = The 66th Kinkless Tetrode designed; KTW63 = the 63rd Kinkless Tetrode-Frequency changer (multi-electrode) valve designed.