View Full Version : Zenith TV date and tube code discrepancy?


drh4683
10-19-2008, 06:58 PM
I thought this was rather interesting to discuss as its something I've never seen before. We all like to determine the time of manufacture of our TV's or tubes via date codes. Here I find something that makes no sense at all. The TV in this example is the '69 zenith I picked up at the estates last weekend. There is a tag on back of the TV, which I took a photo of. Look at the date when the set was purchased, 1-25-69. Also, look inside the set, the cabinet was built 1-7-69. The set was still hot off the press when it was bought from what I can tell.
Now take a look at the 6KT8 in the photo, its date code is 69-13. ALL of the tubes in this set are dated 69-13, and a few others are dated 69-09, which is normal to see a few tubes with different date codes that are close to each other. These are. What I don't get is how can the TV have been bought before the tubes were made? Does this code for tube manufacture really represent the month they were made? Or does the tube code represent something completely different? 9th week would have been the 1st week of march, 13th week would have been 1st week of April. Something doesnt seem right, and these are original zenith tubes. Zenith tubes printed in red ink mean they were service/replacement tubes.

MRX37
10-19-2008, 07:48 PM
Someone might have put in a set of tubes from an earlier made one...

Eric H
10-19-2008, 09:38 PM
Maybe the chassis was swapped at some point in time?
Does the CRT have a date stamped on it other than the paper tag?

Also, would an employee have to purchase a set from a retail outlet or could they buy it right from the factory?

TinCanAlley
10-19-2008, 10:02 PM
It's quite possible those tube are not the originals. Someone could have "shotgunned" all the tubes tracking down a problem. Since many repair places buy their tubes in bulk, they'd probably have all those tubes on hand and they all just happened to fall into those two date codes. :scratch2:

eberts
10-20-2008, 02:27 AM
The tubes were made in 1968, at the time, tubes were dated a year in advance for warranty purposes.
That was done that way because you would not believe how many thousands of set owners would try to get a free tube one day before a warranty expired.

Eric H
10-20-2008, 05:04 PM
Maybe she got the set "One piece at a time, and it didn't cost her a dime" :D

drh4683
10-22-2008, 10:12 PM
Maybe she got the set "One piece at a time, and it didn't cost her a dime" :D

Maybe if Johnny Cash got the set......:D

But here's some more proof that the tube(s) date code is bogus. I agree with eberts. Definitly a warranty related scam/reason to date the tubes newer than they should be. I took the back off my chroma II today to see what the deal was with the power switch and just try to repair it as Im having no luck with a replacment. Anyway, I noticed the CRT dated 77-03, yet the set was made in October of '75 according to the back cover tag. I think its safe to say trying to pin down a date of manufacture off a CRT is completely inconclusive. Chassis tubes are a little closer, but still. The only way to know the real age is by the date stamp inside the cabinet if you're lucky enough to find one.

And did you ever notice tubes were never dated with oddball month codes? Time and time again I see "68-48, or 68-39" You see the same month codes all the time. How come I've never seen 15, 20, or 31 month codes for example? This goes for all the tube makes. Always though that was strange. The pre-dating makes a little more sense now as to why things are the way they are.

zenithfan1
10-23-2008, 08:50 AM
You know.....you're right. I've never seen any 15, 20, 31 ect. date codes either. Never gave it much thought till now, very interesting. I think eberts might be right on with the whole warranty thing.

Tom Bavis
10-23-2008, 09:00 AM
69-13 usually means "1969, first quarter". Some dated by actual week, but many just used weeks 13, 26, 39, 52.

andy
10-23-2008, 09:39 AM
...

kbmuri
10-23-2008, 01:17 PM
Isn't somebody doing their math backwards? If you were running a scam to cheat on your warranty, you'd want the date codes on your tubes to be older not newer. Making the manufacture date newer would extend the warranty, not diminish it.

I see 13/26/39/52 all the time too. So if they just dated the tubes with what fiscal quarter they were in, you could get some tubes that appear newer than the TV, without having to resort to some sinister conspiracy theory. Drh's example would conform to this method. The tubes were made in the first quarter of '69, the TV was sold in the first quarter of '69. End of story.

bgadow
10-23-2008, 01:49 PM
Agreed, that makes the most sense. I've seen plenty of sets where the date codes were in line with the sell date, or the release date of what was a new model.

I have spotted several GE sets from the early 70s where the tubes have 2 different dates, often with one stamped upside down. Maybe they were pulling old stock off the shelves and using it up, but didn't want it to look so old?

drh4683
10-23-2008, 06:25 PM
I think the word scam was the wrong choice of words on my part, as a scam implys deceit and cheating. I would assume the date code on the CRT's would represent the date in which the warranty would expire? There seems to be no other reason for the late date code.

Bryan, Ive seen the same with GE sets, two date codes and the dates are rather far apart from each other.

Findm-Keepm
10-23-2008, 09:37 PM
One thing I learned about tube date codes when working at a distributor in the 1980's - there are different schemes for OEM tubes (installed at the factory) and distibutor tubes (sold at a parts distributor) codes. GE was famous for this - the TV/Radios had a block of letter codes and the distributor tubes had their own as well. RCA used three-letter codes for distibutor stock at one time, then later made all tube codes "numbered" (yr-wk). Some audiophiles will argue that an "RTN" date code sounds better than an "RSN" tube. A-yep, I sold many sleeves of 12AU7 tubes only after the audiophile went through them, cherry-picking date codes.

The reason was simple - distributors were not to honor OEM warranty, nor was the OEM warranty program to honor distributor tube warranties.

GE distributor stock often had both date code schemes (two letter distributor codes) and the yr-wk OEM code. The reason? Simple - the Owensboro tube plant had one line, and put the OEM date code on for the Utica/Syracuse and Portsmouth plants, and any overruns went to distributor stock after adding the distriubutor date code. 67-14 = OEM code. 'EH' = distributor code

I only wish I still had the "gouge" sheet we used to decipher the codes for GE tubes.

BTW, my GE portacolor has all the originial tubes, based on the OEM codes.

Cheers,

Findm-Keepm
10-23-2008, 09:48 PM
I found a reference to the two-letter distributor codes:

http://www.geocities.com/rxtxtubes/pa01017.htm

At the bottom - their discussion about the codes (letter vs yr-week) is incorrect -

Cheers,