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RCA Octagon dating

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trobbins

trobbins

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Joined 2009
dalmura.com.au/projects/amplifier.php
I have a pair of RCA 7027A. The black base has BZ code, which indicates May 1968 from:
http://mysite.verizon.net/tubetronic/PDF_FILES/RCA DATE CODES.pdf

The reference by Ludwell Sibley also refers to a date code embedded in the octagon surrounding the type. The octagons on my valves have a break in a corner, and in a straight part, but the reference gives no further enlightenment on interpreting the octagon date code.

I note that Jeff West hasn't come across the code crack (Dating old tubes...any tips? - Page 2 - The Gear Page). So maybe this is one of those mysteries never to be deciphered ??

Ciao, Tim
 
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