OK, so when I asked about the bias setting on the Lumleys, Keith suggested
that the owner should be running Svets in there, as did several others, so I
went looking for some sources and prices. Watford Valves have some " Cryo -
Treated " Svet 6550C's for a couple of quid more than the 'standard' types.
See

http://www.watfordvalves.com/products.asp?id=10

This is a new one on me. Has anyone tried them ? Is there really any sound
or performance improvement from them ? Or have they maybe been cooled in a
big vat of the snake oil that everyone on here is so fond of talking about ?

Arfa