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GEC date codes

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EC8010

EC8010

Ex-Moderator
Joined 2003
#1
Does anyone know how to crack the GEC date codes? I have reason to believe that "H" is before 1954, "L" before 1955, and "M" before 1957, and can contruct a table using those assumptions that might be right, but does anyone know the definitive answer?
 
#2
Hi,

Oh, dear...wish I could help you out on that one.

None of my books mention that manufacturers' dating code...Philips and associates, yes..but GEC?

Aren't there any company archives?
Maybe radio collectors or Hams could help you out...

Cheers and good luck,😉
 
#4
Eureka?

Yes. That's exactly what I've worked out! I worked out my codes by having some valves with BBC acceptance dates on them, but I had to do a few nudges to make them fit. I enabled this by assuming that the Beeb (mighty corporation although it is) could buy and accept valves a year or two after manufacture, they couldn't do so before...

So, my question is, where did your decoding come from? Did you do the same as me, or did you have a more concrete source?
 
#6
Brilliant!

So in that case, there's a good chance that the following is correct:

A 45
B 46
C 47
D 48
E 49
F 50
G 51
H 52
J 53
K 54
L 55
M 56
N 57
P 58
Q 59
R 60
S 61
T 62
U 63
V 64
W 65
X 66
Y 67
Z 68

I've not seen a GEC valve stamped 69, but I have one stamped 70.

Edit: Even better, this suggests that it was between 1961 and 1962 that GEC abandoned "smoked" in favour of "clear" glass KT66.
 
#7
as far as smoked vs. clear glass goes, lets " clear " that up. the story behind clear vs. smoked glass is a series of well planned and intentional myths perpetrated by the military, in this case a good thing. smoked glass was a military requirement to block the light of the tube being seen by the enemy, thus revealing their position. that simple. no radiation shielding, no heat control or any other old wives tale. so unless you are concerned about snipers, ( real or imaginary ) it makes no difference. want one more you say ?, in ww2, the us military kept the very advanced norton bomb sight a secret by saying the bombing accuracy was due to feeding the bombardiers very large helpings of carrots at every meal and the large doses of vitamin k resulted in extraordinarily superior eyesight.
 
#8
smoked glass was a military requirement so the enemy couldn't see the tube lights, thus revealing their position. all other explanations were purposely reported to divert attention from the truth ( in this case a good thing ). so if you're not concerned about snipers ( real or imaginary ) either clear or smoked will function the same
 
#9
I'm so glad you cleared that up.

But nobody in this 15 year old thread mentioned "smoked". Rude to change the topic.

On indirectly-heated tubes, the enemy would have to be in the same room to see the glow.

I believe I have seen smoked 6V6 from the 1930s, when the US was at peace, Poland and France not using US tubes.

If you have lived with an open-back old radio, you know they throw light up on the wall behind them, obvious in a dark room. Smoked would have reduced this unwanted wall-shine. (AC/DC radios didn't shine as much because they were closed-box.)
 
#11
I have some WWII 5930/2A3W with carbon emulsion coated glass made for use with field radio sets (or so I'm told. I wasn't there myself.) (Data Sheet here) They sound a little different than the standard ST shaped 2A3 with the same type plate structure.

I found this in RCA Electron Tubes Vol 1 at Tubeboks. Perhaps it has something to do with the difference or perhaps not. Interesting read though.

"The inside surface of the pentode bulb is
coated with carbon to reduce the emission of secondary electrons which
results from the bombardment of this surface by primary electrons
which escape through the interstices between tile mica spacer and
plate. This is particularly important at the lower frequencies, where it
is desirable to keep the high load impedances from being shunted by
the additional plate losses introduced by such effects."
 
#12
EC8010 said:
So in that case, there's a good chance that the following is correct:

A 45
B 46
C 47
D 48
E 49
F 50
G 51
H 52
J 53
K 54
L 55
M 56
N 57
P 58
Q 59
R 60
S 61
T 62
U 63
V 64
W 65
X 66
Y 67
Z 68

I've not seen a GEC valve stamped 69, but I have one stamped 70.

Edit: Even better, this suggests that it was between 1961 and 1962 that GEC abandoned "smoked" in favour of "clear" glass KT66.
Click to expand...


Thanks for this informative post!

So, how should I read my pair of GEC U52's with codes "JE 4" and "LD 4"? The J one year 1953 and the L one year 1955? Can the other two characters of the code be translated, as well?

Thank you!
Gianluca
 
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