I think I had this in an Eico 720 back in the sixties.
Thanks for the info.
I'll have to scrounge around for a RCA transmitting tube manual ;-)
Do you still have a rig that uses a single 6146? It looks like this tube would work. Basing, Mu, Transconductance, inter-electrode capacitance are all identical.
You probably did use it in the 720.