[sdiy] parts numbering

[Roy J. Tellason]

Somebody posted in here a bit earlier abotu Tillman's pages,  and I'm looking 
around over there.  His guitar amp circuit specifies a FET with the number 
J201.  Reminds me of one I ran across in some synth or other that was a dual, 
E402?

Anyhow,  my question is,  whose numbering system is this?  Who made these 
parts,  originally?

A source of datasheets would be welcomed too.