Idenitifying tubes, testing tubes
Dec 11, 2009 at 1:13 AM Thread Starter Post #1 of 24

eruditass

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I just got some used 6680 and was quite excited only to realize there is nothing on them or the box that says 6680 (though it could be faded). Only thing I see is GE symbol, and 12 AU7.

Also, is there a general way to test how "matched" these tubes are?

Thanks!
 
Dec 11, 2009 at 1:24 AM Post #2 of 24

FallenAngel

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Honestly, not really, you can look at construction to see what type of tube it is, but I would just ask for advice from tube gurus that remember what the tubes look like. :p

As for matching, it's mostly pointless, most tube testers don't test tubes in the same conditions as they will be used in an amp so even if you match in some scenario, sticking them in an amp may run them in completely different conditions.
 
Dec 11, 2009 at 1:53 AM Post #3 of 24

tomb

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Quote:

Originally Posted by DoomzDayz /img/forum/go_quote.gif
I just got some used 6680 and was quite excited only to realize there is nothing on them or the box that says 6680 (though it could be faded). Only thing I see is GE symbol, and 12 AU7.

Also, is there a general way to test how "matched" these tubes are?

Thanks!



If it says 12AU7, I doubt that they're 6680's.
wink.gif


As for testing, of course - there are many tube testers on the market. The best ones test for transconductance or micromhos, which is a better indication of the tube's output than a simple emissions tester, which basically tests just to see if the tube operates. So yes - a good tester can test for tube output at the design center ratings of the tube or somewhere similar.

However, FallenAngel is correct in that the real test only occurs when you place them in an amplifer, but you can get some better assurance by testing/matching them in a tube tester first. If they're mis-matched on the tube tester, chances are you're never going to have a match when you put them in the amplifer. On the other hand, if they are matched on the tube tester, you have some assurance that there's a good chance they'll operate close to that. That's assuming the amplifier is using them somewhere close to the operating design points for that tube type. The further away from that design center point/tube tester point that the amplifier design operates, the less chance you'll have that the matching will be consistent.
 
Dec 11, 2009 at 3:08 AM Post #4 of 24

les_garten

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I kinda agree with these guys about the tube testing and kinda don't. 99.9% of the Junk out there is not a REAL tube tester. There are about maybe 5 testers that can test a tube properly. Most of those only test at relatively low voltage and current.

But that doesn't mean that if you have a good tester that you can't put it to good use. A shorted tube may take your gear out when you power it up. Testing for performance and matching with the top two testers out there I think has a lot of use.

Here's what I have:Triplett 3444

I would consider it the #2 tester out there behind this one: Alltubetesters.com | Tester Sales

Both of these can put a tube through it's paces, but not as much as an amp can.
 
Dec 11, 2009 at 3:15 AM Post #5 of 24

eruditass

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Thanks for the replies!

I figured as much, just making sure I didn't miss out by getting cheaper unmatched tubes.

I took a picture of the tubes and boxes:

33xhrbo.jpg


Tubes say:

12
AU7

Of course there are lots of GE 12AU7 tubes(?)
 
Dec 11, 2009 at 3:17 AM Post #6 of 24

les_garten

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Quote:

Originally Posted by DoomzDayz /img/forum/go_quote.gif
I just got some used 6680 and was quite excited only to realize there is nothing on them or the box that says 6680 (though it could be faded). Only thing I see is GE symbol, and 12 AU7.

Also, is there a general way to test how "matched" these tubes are?

Thanks!



What is labeled what? Does the tube have 12AU7 on it? The box may not match the tube you know?
 
Dec 11, 2009 at 4:51 AM Post #8 of 24

eruditass

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frown.gif
Can you describe the differences?

From what I can tell on the tube (most of it is faded), above the GE symbol is where it says 12 AU7

I did find on one of the boxes it says 6680 12AU7, but the other only says 12AU7.
 
Dec 11, 2009 at 4:57 AM Post #9 of 24

les_garten

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Quote:

Originally Posted by DoomzDayz /img/forum/go_quote.gif
frown.gif
Can you describe the differences?

From what I can tell on the tube (most of it is faded), above the GE symbol is where it says 12 AU7

I did find on one of the boxes it says 6680 12AU7, but the other only says 12AU7.



Very Similiar if not the same. Sounds like they are the same tubes

TDSL Tube data [6680]
 
Dec 11, 2009 at 2:12 PM Post #12 of 24

TimJo

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I took a look at mine and the etching is 12AU7A with the 6680 a part of the painted label. The painted label also has LF 188-5 on it, but I have no idea what that signifies. Maybe a factory date code thing.
 
Dec 11, 2009 at 4:25 PM Post #13 of 24

n_maher

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Quote:

Originally Posted by les_garten /img/forum/go_quote.gif
99.9% of the Junk out there is not a REAL tube tester.


I don't really agree with that statement.

Quote:

But that doesn't mean that if you have a good tester that you can't put it to good use. A shorted tube may take your gear out when you power it up.


To me, first and foremost this is what you want a tube tester for. If you buy used tubes without a tube tester all can say is good luck and you're braver than I am. I own two testers, together they cost less than half what either of the two you linked to would. Do they test tubes at every operating point? Of course not, but they can give you an idea of a)the general lifespan that might be left in a tube and b) the performance of tubes compared at similar operating conditions. While the tested operating point is certainly different from the actual end-user application it's not exactly worthless or JUNK.

FWIW I have a Jackson 648S and US Army Signal Corps I-177 (man'f by Hickok) and they cover the vast majority of the tubes I've come across.

Of course it is also worth nothing that finding a good, reliable tube tester is no easy task. While there are many on Ebay there are very few that I would actually buy.
 
Dec 11, 2009 at 6:19 PM Post #14 of 24

les_garten

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Quote:

Originally Posted by n_maher /img/forum/go_quote.gif
I don't really agree with that statement.


To me, first and foremost this is what you want a tube tester for. If you buy used tubes without a tube tester all can say is good luck and you're braver than I am. I own two testers, together they cost less than half what either of the two you linked to would. Do they test tubes at every operating point? Of course not, but they can give you an idea of a)the general lifespan that might be left in a tube and b) the performance of tubes compared at similar operating conditions. While the tested operating point is certainly different from the actual end-user application it's not exactly worthless or JUNK.

FWIW I have a Jackson 648S and US Army Signal Corps I-177 (man'f by Hickok) and they cover the vast majority of the tubes I've come across.

Of course it is also worth nothing that finding a good, reliable tube tester is no easy task. While there are many on Ebay there are very few that I would actually buy.



I think my 99% statement is pretty close. Look at 100 Ebay Auctions and 99 of them were useless the day they were made. Don't hold me to exact numbers here, but you get the idea. Type in "tube tester". I feel it's much better to warn someone who might buy something with a bunch of knobs thinking they are getting something useful. The 177 you have is serviceable, the Jackson is one of the only two non transconductance meters that is somewhat usable, with the other being the BK 747.

Fun Tester reading: Tone Lizard
 
Dec 11, 2009 at 8:00 PM Post #15 of 24

n_maher

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Quote:

Originally Posted by les_garten /img/forum/go_quote.gif
I think my 99% statement is pretty close.


Just about any tester you can buy (provided you are intelligent enough to buy one that tests the tubes that you want to test) can test for shorts. You call that useless?
 

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