I remember the 6CW4 well. I think they were use in the 'plug in' modules in my first Tek 'scope. The ones I was think of were much like the double tride shape in the same web page, wire ended pentodes, not much thicker than a pencil with 7 thin wires for connection. Apart from the heater power requirement, they out performed the 'high tech' germanium transistors of the day. I used to listen in to WNYW and Boston stations across the Atlantic on MW with my EF74 TRF receiver which curiously, and because of what I could get my hands on at the time, had an op-amp audio stage, if I remember, it was a Fairchild uA701.
By the time I had ventured to higher frequencies, the only viable amplifier I could get was the 'Acorn' tube, worked nicely but a pain in the rear end to mount!
Brian.