George,

I have a Drake TR-3/RV3/AC-3 combo that did well for me in the 1970's.
It was designed for a matched trio of 12JB6 sweep tubes as the final
amplifier.
Obviously, these bottles are hard to find, and a matched trio even
harder. It's to a point where the current finals can't be neutralized.

You might check with Antique Electronics Supply and RF Parts -- both of
them at one time would match sets of 6JB6s for a fee ($5.00 per tube?).
Also Bruckner Components (http://www.powertubes.com/5Rcvg.htm) may be
able to match a set for you.

Northe
N6KO
Green Valley AZ