[whubbard]

Hi,

I'm looking to buy a pair of siemen's 7308s, and I've found a good seller who has tested the tubes. Here are the results:

Tube1 - A1 = 18,0/13,0 A2 = 18,0/13,0

Tube2 - A1 = 18,0/13,0 A2 = 18,0/13,0

Both tubes have A6 9C stamped on small plates inside. If you know how to dechifer the siemens codes please share that information with me.

For a 7308 is this good/bad? It will be used in an aspen GK-1.

I can guess by the numbers that these tubes are obviously matched, but is this 18/13 good. (frankly, what does it mean)

Also, I read abou it somewhere else, but I believe A6 means it was the 6th production, I've heard the 4th was the best, but for the price, I think these will be fine.

Thanks,
West

[Steidl Guitars]

I suspect that each triode is being reported as a pair of values: as tested/minimum. 

That is, each triode (there are two per tube, indicated with A1 and A2) tested 18.0 with a minimum good value of 13.0 (which would be constant).

The question I would have is what does a new 7308 measure on this tester? 

[whubbard]

Well they are NOS so I'm not sure it would do any good to test new 7308 as they wouldn't be the same.
what exactly does the 13 out of 18 mean though. I don't understand what the 'minimum' means. Would you mind explaining it a bit?

Thanks,
West

[Steve]

Hi,

     I  would guess the numbers 18 and 13 are some relative scale. It may or may not mean anything like Gm or Mu. However, it does seem to indicate some differences between the two triode sections within the envelope. How close or far apart in terms of Gm or U, or simply plate current, I don't know.

Hope this helps.

[Steidl Guitars]

Well they are NOS so I'm not sure it would do any good to test new 7308 as they wouldn't be the same.

For many tube testers, there is a level established as a standard value for a new tube.  For 6SN7s on my tester, that is about 2200 (obviously a different scale than the tester being used here). 

If a tube tests below this value then it is probably not new (tubes can test above this value).  I was asking if there was such a level established as new for the tester being used here.  If you are sure these are NOS, then forget about it. 

On each tester there is also a value below which a tube is not considered usable.  I was suggesting that's what the seller was indicating with the number to the right of the slash (13).  The number before the slash is the reading he is getting for the tube being tested (18).  Therefore, these are testing 18 where the minimum usable is 13. 

Because each of these tubes has two triodes, the seller is reporting the test value followed by the minimum usable value (tested slash minimum).  In every case, the triodes here read exactly the same (18). 

As Steve mentioned, the scale used here is some sort of relative scale.  I disagree with his interpretation of the results though and I think instead that every triode tested identically at 18 units (whatever they are).

Although I think I have this right, I could well be wrong, so you should ask the seller exactly what these numbers mean relative to the tester he is using.  That's the only way to know for sure. 

[Steve]

I misread the initial post, should have studied it more instead of just glancing at it. Thanks Steidl Guitars for pointing that out. Yes, I agree, 13 is probably the min considered good, whatever, and 18 was that the sections were above that, indicating above min.

And 18 for both sections seems to indicate both are quite well matched.

Thanks again Steidl.
Steve

[Steidl Guitars]

Steve, my pleasure. 

I thought you might have misread it, but you had me second guessing myself as I was pretty darned sure you knew your way around tube testers!

Bob

[whubbard]

Thank you all for you help. It appears that you are saying the tubes are good, but I might inquire a bit further with the seller.

if it helps they were tested with an AVO mark IV.

Thanks Again

-West

[Steve]

Steve, my pleasure. 

I thought you might have misread it, but you had me second guessing myself as I was pretty darned sure you knew your way around tube testers!

Bob

Hi Bob,

     Well, I have to admit it has been decades since I have even seen a tube tester. I normally have or build my own circuit, compare sections by varying the bias and plate voltage, apply different signal levels, stuff like that, and work from the info.

Take care Bob.