(!!!) (Best Single) CX-299 Cunningham engraved base NOS 1920's (2.9ma) (X-99=UX-199=CX-299)
(!) (Recommended Single) X-99 RCA Cunningham Radiotron engraved base NOS 1930's (2.5ma) (X-99=UX-199=CX-299)
(!) UX-199 RCA Radiotron NOS original box 1920's (2.3ma)
(display tube) UV-99 Radiotron brass base 1920's - lights up but does not have emission
(display tube) UV-99 Radiotron brass base 1920's tarnished base - lights up
(display tube) UV-99 Unknown maker - does not work
99=X-199 Silvertone NOS 1934 (2.5ma, Gm=500) (strong single)
99=X-99 RCA Radiotron NOS 1930's in sealed box (2.2ma)
CX-299=99 Cunningham NOS 1930 era (2.1ma)
UX-199=199 RCA Radiotron NOS 1930 era (1.7ma)