BCL is correct....if you just blindly substitute 6146B's in a rig that was designed for 6146A's you can run into serious problems...go here for an article on the 6146
family of tubes   http://home.comcast.net/~k9sth/The_6146_Family_of_Tubes_1.htm

73...Tom WA6OML

just received my new QSL cards from Kiril at qslcanada.com.....very quick service...had my 1st proofs approx 1 hr after submitting my custom design...had final
proofs after only 2 hrs....placed order on a Monday & had
cards in hand by folowing Saturday...very nice person to deal with & Kiril is also a Ham (VE3AXC), so he's interested in a quality product at an affordable price...
give him a try, I know you won't be disappointed....
my custom color cards cost me $9.99/100 + $8.00 shipping from Canada to New Mexico....

73...Tom WA6OML

p.s. if you want to see a sample of my card, send me an e-mail....