dje: BUT the PG 6/9000 green WILL work in his 6/9200. The ONLY reason a 6/9200 tube won't work in a 6/9000 is because there is physically not enough room for the longer tube, but they do function totally compatibly, as I've actually installed an XG green in a PG 6000. It *just* fit, with the neck board butted right up against the back, but it did function exactly as it should have. Why you'd want to put an XG or PG Extra green in a PG permanently, I don't know, but if you had no choice, I can say from my experience(experiment) that it will work. To put any older tubes in a newer machine is no problem.
Also, outside of Australia, the XG tubes are priced several hundred MORE than the PG Extra tubes even though the green is exactly the same.