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Old 29th September 2015, 02:35 PM   #1
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Default Current production tubes testing used/low out of the box?

I have been selling vintage tubes for quite some time now and am very familiar with them. I have a variety of testers but I mainly stick to a few calibrated TV-7s. It's the new production tubes that I need advice on as I just acquired a collection of them.

When they arrived about half were in their respective boxes. Some were loose, some bulk packed. They all looked good as far as the getter flashing goes. A few looked used but for the most part they looked as I would expect a new tube to look with no scratches on the bases or fingerprints on the glass.

I tested a few hundred different types (EL34, 12AX7, 6L6, 5AR4) and nearly half of them test in the used range for Gm with a TV-7. I have a digital tester in the mail that will allow me to read lp. The best I could do was to throw the EL34s in an amp. All of the ones that didn't read NOS for Gm didn't need to be rebaised in my amp which was running close to NOS tubes so that leads me to believe they are putting out the right lp.

Also, every single JJ 5AR4 tested extremely low for emissions on one side and several were arcing. I read somewhere that there was infarct a bad batch of these that got out in the early 00s.

Does anyone have experience in going through large batches of current production tubes? I have heard of Chinese tubes being DOA but is it really this common for large amounts of them to test used like this?

I can't tell if I got screwed and most of this stuff is just used or if it's just common for brand new tubes to test used out of the box, especially for Gm and Emissions. Again, these tubes look perfect, sound perfect and seem to be putting out the right plate current for being new.
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Old 29th September 2015, 09:55 PM   #2
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Some current production tubes suffer from "sleeping sickness". The cathodes are not fully activated. You can try "cooking" the tubes on a high heater voltage, say 25% above nominal. With luck, the cathodes will activate.
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Old 29th September 2015, 10:51 PM   #3
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Sleepy Cathodes could very well be the cause here. I just got off the phone with New Sensor. They told me that for a variety of reasons many of their tubes won't test right on vintage tube testers. I think that's their way of saying that the quality of the newer tubes just isn't there.
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Old 30th September 2015, 01:05 AM   #4
lexx21 is offline lexx21  United States
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Quote:
Originally Posted by DistortedSmooth View Post
Sleepy Cathodes could very well be the cause here. I just got off the phone with New Sensor. They told me that for a variety of reasons many of their tubes won't test right on vintage tube testers. I think that's their way of saying that the quality of the newer tubes just isn't there.

I believe that you are absolutely correct. That would be like saying that you can't test a new duracell battery with a vintage volt meter. If their products were up to spec with the originals, they they should test as such.
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Old 30th September 2015, 03:02 AM   #5
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by lexx21 View Post
That would be like saying that you can't test a new duracell battery with a vintage volt meter.
Nice! Thanks for the laugh.

Just as a sanity check, one could trace out a couple of the characteristic curves using a power supply and a couple of multimeters. If the new tubes are dramatically different from their data sheets, you should have a good case for a return. It would be interesting to see the data for sure.

Tom
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Old 30th September 2015, 04:58 AM   #6
JMFahey is offline JMFahey  Argentina
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Truth is many current production tubes are poor quality, period.

Any different "explanation" offered by sellers is plain and simple BS, no tube will remain unsold no matter how out of spec it is.

"Unactivated cathodes" they claim?
"Don't test them?"
No kidding !!!!

Don't throw a blanket statement over Chinese tubes, you'll find them in all qualities, from ugly to very good.

I have had problems with most of them, (except Ruby, who seem to test all tubes and plain not sell bad ones) and sometimes, to avoid later futile claims by customers (who argue *I* sold them the tubes) , I ask them to buy their own, usually Fender branded if available.
Not the best, not the worst, but at least all functioning so far, clearly they test them before packing.

As of JJ, which initially were considered best quality, things go so bad that if I need to replace, say, 4 x EL34 in a 100W guitar amp, I ask customers to buy 6 and bring them, which I then test before their very eyes.

Typical is to get 4 quite good and even ones, which go straight to the amp, a somewhat weaker one which is suggested to be kept as a spare (in the future the somewhat used good ones will go down in properties and match the spare ) and an even weaker one, only usable as an emergency Saturday night, all shops closed replacement , just to finish a show, and to be replaced Monday morning.

The only way I will sell tubes again is if I import them myself, straight from Factory, in, say, 200 or 300 unit batches, measure them myself and eat the bad ones.
Only way I can guarantee the good ones to end customers.
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Old 30th September 2015, 04:02 PM   #7
w5jag is offline w5jag  United States
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I was testing some tubes Sunday (TV-7/D) and since I had it set up for 12AT7's, I put in a new (NOS, now, I guess) Ei "Elite" 12AT7 with the gold pins, presumably from one of their last runs, and both sections measured about 1/3 of the discard value for that type.

I left it sitting in the tester for a while, and it came up some, so it may have "sleeping sickness", or it may just be a crummy, bad, tube out of the box.

I have a fair degree of confidence in my TV-7. I got it depot overhauled and calibrated; I was the person to open the depot sealed carton.

I have a lot of old production tubes. I have a good smattering of new production tubes. I think the quality of the new ones is really hit and miss, my experience, about 50/50 hit/ miss.

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Old 30th September 2015, 05:28 PM   #8
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You guys have all pretty much confirmed what I had suspected. After calling New Sensor I was told that their tubes just won't test as NOS on a TV-7. It's pretty discouraging to hear that even the manufacturer doesn't have faith that their products will test up to spec.

I did buy these as a sort of close out deal. I think I received that companies slow moving stock and some rejects.

This is why companies like GT, TAD and Ruby exist. You are paying extra for them to screen the tubes for you.
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Old 30th September 2015, 09:46 PM   #9
TheGimp is online now TheGimp  United States
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Easy test for the cathode is to put a couple of weak tubes in an oven at 350F (177C) for four or more hours, then shut the oven off and let them cool slowly. Then retest and see if they test any differently.

I've done this with old Soviet Union era tubes and found fewer problems by cooking them before testing.
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