People here have recently mentioned tubes intended for portable
operation, with plate voltages of around 20 volts. Much more common are
tubes intended for running from mains-powered supplies. These mostly
require plate voltages that can be lethal. You should consider this when
designing kits for kids.

Roy Lewallen, W7EL

Bruce Kizerian wrote:
Thanks everyone for the interesting and useful information.

For the record, I am not particularly in love with tubes, but if there
is something they will do better than solid state devices I'm willing
to give it a try. When I can buy PN2222 bipolars for $.02ea and PN4416
JFETS two for a quarter, and dual gate MOSFETS for a nickel, the
expenditure for one of those fragile glass things better be well worth
it. It can' be different or just a little better. It has to be "knock
your socks off" superior...I make radio kits for kids and schools and
I want them to be able to afford the purchase.

Bruce kk7zz
www.elmerdude.com