I always understood "big pin" tubes to be those made before octal
sockets were introduced. Many octal tubes are essentially the same as
earlier "big pin" tubes except for the sockets and dimensions of the
glass envelopes.
Big pin tubes could have four or more pins, as many as six (maybe
more) and often top caps for grids or plate. The pins of big pin tubes
were not all the same, usually two were larger to "key" the tubes so
they would fit in only one way.
I don't know the date when octal tubes were introduced, sometime
around the mid 1930's I think. It seems to me that metal tubes were
introduced not long afterward. A little later came "locktal" tubes,
introduced by Zenith (again by memory and could be wrong). These were
similar to octal base except had locking pins and a metal base. Many
similar types were made with both bases (and different numbers). Loktal
base tubes were popular for automobile radios where they tended to be
more firmly connected.
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On 4/2/2025 2:20 PM, don Root wrote:
Hi Jim, I have been trying to reply but keep getting diverted.
One problem is understanding the definition of a “big pin” tube. How big
is “big”? ?I can find no definition. the 4,6,and older 7
Ing tubes have two ?0.156 ?[5/32?] inch pins and some .125 [1/8]inch
pins but the 5 pin tube has only the smaller pins.
Anyhow, I googled with “what is? a "big pin" radio tube?” and AI replied
as follows”
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
