TUBE TEST values

[pzm9pzm9]

hi,

From what I understand, the mutual conductance value of a tube will vary everytime you measure it (even with same tester). Is this true?

How likely is it that all 4 tubes have tested values that are exactly same when tested for second time?

I ask this because I recently bought 4 tubes from ebay and paid extra for double test and marking them on each tubes. Just received tubes today and found out that actual conductance values marked on tubes are exactly same as the values that initially the seller provided on ebay. If this person have done the test upon my request, for re-testing tubes, shouldn't the values be a little differ from the first test values?

Thanks in advance

 

[Hirsch]

Sometimes values change, sometimes they don't. I prefer it when values don't change between tests. Odds are better that I had the tester set up correctly. Some of the variance may be due to continuous potentiometers in the tester, that can never really be set to exactly the same value once moved. If you haven't moved them, you're still at the same value.

Also, bear in mind that the degree of sensitivity of the tester itself may not be precise enough to pick up very small changes.

If ALL conditions for testing are exactly the same (not always possible on some testers), and the tube has been given time to warm up and stabilize for both tests, identical measurements would be expected, provided the tube has not been used between the tests.

Did you get what you paid for? I have no idea. However, the idea of actually paying money for a second test of previously tested tubes would never have occurred to me. A good seller will have repeated the test. OTOH, a good and ethical seller would have gotten good test values the first time around, and might also have tried to dissuade you from paying for an unnecessary test.

 

[pzm9pzm9]

Thank you for the clearification.
I bought 4 tung-sol 5998 from e-bay and after I won, I wanted make sure that the tubes were marked for their test values. (because only 2 were matched) I have no tube tester or anyone around to test them. So I e-mailed him to make sure values were indicated, and he told me they were already packed and they were not marked.... So I had to pay him extra for testing second time and re-packing.
Anyway, I ended up getting 4 GREEN tung-sols by their mistake. They were supposed to be white printed.... But I liked the SQ of these so decided to keep them.
This was my first ever buy from ebay and I ended up paying too much for a matched pair of tung sol.

 

[Hirsch]

That's a bit different. If the tubes had not been marked, you were paying to have the seller reopen the boxes and redo the tests for marking purposes, not to validate the previous test (although the seller should have had the test results with each tube the first time). You may not have overpaid. It all depends on what the final auction price was, and whether you like the sound.

There are a number of very good tube sellers on eBay, but it takes some practice to learn who they are. If you don't own a tester yourself, it's usually best to buy from a reputable dealer because some of the sellers on eBay are a bit less than careful about checking their tubes.

 

[pzm9pzm9]

yes. I was thinking of getting a tester, but accurate ones cost near $300.

I got into this head-fi hobby not too long ago, and I am starting to bit worry about my spending habits on gears and tubes. I am having so fun finding tubes on e-bay or from else where. I have mixed feeling about this. Oneday, I love it: other days, I somewhat regret for spending hundreds of dollar on them. After all, what I get is still a music.