While looking thru my copy of "GE Essential Characteristics" I noticed some letters and letter combinations that were avoided. For #xy# x and y were never the same letter. No 6BB6 for example. Other letters were never used at all, like I and O for obvious reasons, but P was also never used except in the early days. 1P5, 6P5 and 6P7 was it. No 6BP5 for example. P and R look similar, but so did E and F and both of those were used. Looks like the tube era ended right at 6MV8. They never made it to 6QA5 or such. Given the pattern, they probably would bot have issued 6PA6...:scratch2:

The missing "p" designation may be due to possible confusion to phosphor types in CRTs?
A 6BP5 could be a 6" jug with P-5 Phosphor.

jr

While looking thru my copy of "GE Essential Characteristics" I noticed some letters and letter combinations that were avoided. For #xy# x and y were never the same letter. No 6BB6 for example. Other letters were never used at all, like I and O for obvious reasons, but P was also never used except in the early days. 1P5, 6P5 and 6P7 was it. No 6BP5 for example. P and R look similar, but so did E and F and both of those were used. Looks like the tube era ended right at 6MV8. They never made it to 6QA5 or such. Given the pattern, they probably would bot have issued 6PA6...:scratch2:

The RMA had a scheme for numbering tubes as shown here:
http://en.wikipedia.org/wiki/RMA_tube_designation
Also more on world wide numbering systems here:
http://www.finance.reachinformation.com/List_of_vacuum_tubes.aspx

Cliff

No 6BB6, but don't forget about the 6Sxx series of tubes, which originated for registration of single-ended versions of grid cap octal tubes. Hence the capped 6S7 begat the single-ended 6SS7.

How about the 6RK47 and 6PI19, etc. (seen in Japanese color TVs in the 70s)?

Charles

How about the 17BB14, usually labeled 17B-B14? Not sure who used them, but I have a stack.

How about the 17BB14, usually labeled 17B-B14? Not sure who used them, but I have a stack.

IIRC, that tube is a horizontal output tube used in a Toshiba built Sears 12" B&W portable.