Made in USA.
At first glance, it seemed to be Tung-Sol round place. Construction is very similar to the round place with black glass but it has diamond shape top mica, dual copper grid posts.
It looks very unusual. Supper sounding same or better round base version.
Tested matched and very high as new. One maeked Tung-Sol and other marked RCA
Made in G.Britain by Mullard (1950s).
Clear glass, Brown base, Bottom D-Getter. Can bring to you the superb sound. Nearly same as 6SN7s family and can be replace for them BUT can be not used for replacing where the plate volate over 300V.
Nos in original box.
Made in USA by RCA (1960s).
Muddy black plate, Triple mica and Double D-Getter with five supports.
Most of muddy black plate version are made by RCA.
Very warm sweet sound, great on voices and jazz. Long life tube (10.000 hours)
Nos in original box. Matched pair are available.