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when reading test results of tubes? (Read 1005 times)
back2vinyl
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when reading test results of tubes?
02/12/18 at 18:51:55
 
What does this mean? What should you look for when buying tubes.

Test results:  83/88, whereas a minimum good on my Hickok Cardmatic tester is 50/50.  These are high test scores.

I see such a difference in price on tubes...

thanks
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Lonely Raven
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Re: when reading test results of tubes?
Reply #1 - 02/12/18 at 19:49:27
 
IMHO, take those test results with a grain of salt. Testing on an old tube tester really doesn't tell you the quality of the tube, just that it works. It could be noisy as hell and still pass.

Most tube testers don't test at the full voltage  that the tube will see in an actual amp.

Most tube testers don't test for noise.

Many of the sellers say "matching" but they don't say what their matching criteria are. Are they "matching" because they came out of the same box? Are they "matching" because they have the same label and date code? Are they matching because a tube tester that doesn't test at full amp level voltage  says they draw about the same, or output approximately the same?


So when you see a description like "Test results:  83/88, whereas a minimum good on my Hickok Cardmatic tester is 50/50."   To me that just says they should work (at least enough to pass the test), and are possibly used/possibly NOS. It doesn't really say anything more than that.


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Steve Deckert
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Re: when reading test results of tubes?
Reply #2 - 02/13/18 at 02:41:08
 

One tip about New Old Stock (N.O.S.) tubes is that the big manufactures such as RCA, GE, SYLVANIA to name a few made tubes for all the radio, test gear and stereo equipment, musical instrument amplifiers, organs, etc.,and put that manufactures brand on the tube.  For example, Hammond organs would use tubes that say Hammond, but they were simply RCA tubes that said Hammond instead of RCA.

On eBay you will see the same tube, one branded RCA and one branded Hammond with as much as a $50 difference in price and they are the same tube.

My advise is to buy off brands like this for cheap to give yourself a good hand full of tubes to experiment with rather than trying to research the best NOS tube and pay way to much for it only to find out it's not that good, or noisy.

Once you get familiar with the specific tubes you like you can justify spending a bit more money on a new old stock one that tests new.

Steve
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back2vinyl
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Re: when reading test results of tubes?
Reply #3 - 02/13/18 at 03:24:43
 
so what do I look for in a 12ax7 tube? Are all 12ax7 tubes triode, are they all balanced? What is o gate mean?
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will
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Re: when reading test results of tubes?
Reply #4 - 02/13/18 at 20:24:30
 
vinyl,

12AX7/ECC82, or 12AU7/ECC82, 6692/E88CC, 6DJ8/ECC88.....etc, are basic names for a type, American/European names as I have written them above, though there are more when you count military designations.

Each type shares design and electronic characteristics...So if you need a 12AX7, all good 12AX7s will function almost the same....interchangeable, being family....but having different sound qualities and balances within that based upon vintage, specific design choices, materials, etc....

This is the beauty of tube rolling once you learn about tubes....You could get three known-to-be-nice 12AX7s....the three made by different companies, or even the same company, but different vintages (therefore construction and material variations), and have three 12AX7 sounds. Or you might find a lesser known value tube you like better!

This is also the gamble, what Steve points to. It may be a tube with a great reputation (and price), with good scores and low noise, and just not suit you as well as another. How a tube sounds is about how it is made, but also how it fits with everything else in your system/room.

Also along the lines of what Steve talked about, you can get some really good prices if the label or variation is less known/prized. You can even sometimes find British/Mullard made ECC88s...and also Siemens made tubes that are labelled RCA or GE, but also saying "made in Germany," or "made in Great Britain." These tubes are usually a good value, one, because ECC88/6DJ8 are generally less popular than E88CC/6922, and the other, that they are off-label.  

Also type variants, or tubes that are electronically similar can be worth learning...Like 12BH7s (often pretty inexpensive) can usually be used in 12AU7 circuits... different, but potentially nice sound. And ECC189 and PCC189, european variations of ECC88 and PCC88s, are generally inexpensive compared to their more known family members, and can sound great in my amps.


I think what you are probably asking about is the getter rather than "gate?" A getter can be on the side, bottom/side, or top of the tube. For small signal tubes it is often on top, coming up off the top mica (the horizontal roundish shaped part that caps the vertical plates). Usually the getter riser is a wire or flat/narrow piece of metal rising vertically (or at a slight angle) off one side of the top mica, and welded to the riser, in this case, would be a horizontal O ring of metal...called a hallow getter, or O getter. Or the getter could have a D shape, a D getter, and more. You can find the getter by finding the silver flash on the tube glass. The getter "flash" comes from a heat/chemical interaction that intentionally creates a silver flash, contributing to, and keeping the vacuum in the tube.



When you have some time, you can find some good things on tube construction on the web.

Among others you can find, an intersting educational tube sales site is audiotubes.com. Brent Jessee has been at it a long time, and you can learn a lot from his site, and/or from talking with him for further clarification. He has many very rare and valuable tubes, but also some pretty good value tubes, and could be worth checking out as you learn the language of tubes. Or perhaps to buy some from a known and reliable seller who stands behind his tubes while you learn the language. I have linked his 12AX7 page since you mention it specifically. http://www.audiotubes.com/12ax7.htm

He also sells on Ebay, as many good sellers do (big and small), and if you get into it, you can find reliable Ebay sellers you like to work with for value and quality.

This is a post I made elsewhere on the forum with some of my take on buying tubes and using ebay.

http://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1504652960/6#6




Speaking of tube testing, noise and defective tubes, the post I linked generally discusses finding good sellers and knowing what to look for in buying tubes....

Over quite a few years, and lots and lots of tubes bought this way, in the rare cases when tubes have been too noisy or otherwise defective, the Ebay seller has replaced them, or given a refund.

I suppose I may have been lucky, but I do check things out carefully, and ask questions if needed....and finally depend on the Ebay system. I believe I have only had to get Ebay to get a tube seller to do the right thing once....the other times something was wrong, the seller setting things straight without intervention.


So it can take some exploration to get more familiar with the languages of tubes, and to get clearer on reliable sellers, but can be a lot of fun if the quest suits you. And sometimes you can find some really great tubes and really good values.
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back2vinyl
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Re: when reading test results of tubes?
Reply #5 - 02/13/18 at 21:18:59
 
Damn man, thanks for taking the time to explain the tube world to me and others of corse. Appreciate it!

All all 12ax7 tubes matched?
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will
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Re: when reading test results of tubes?
Reply #6 - 02/14/18 at 00:53:30
 
Not necessarily. I am no expert, but this is my take on it.

Matching tubes ideally includes testing with a good, calibrated tube tester for single tubes, and includes matching construction and vintage for pairs.

For a single tube that is "dual triode" (two sections in one tube) when the triodes match pretty well, this might be called "balanced triodes," or "matched sections."  Basically, each triode is able to function as a separate tube in the same bottle. This is likely what you are seeing looking at a single 12AX7 tube with two readings....probably the two triodes.

The other primary matching is a "matched pair" or quad of tubes. Often when you look at measurements of a matched pair of dual triode tubes, they will show two numbers for each tube (as with a single tube), but in this case, all four triode measurements being close is the ideal. There is a lot of talk about this, benefit or not, but I tend to play it safer, looking for good electronic matching between triodes, and between a pair of dual triode tubes.

Some tube sellers will not list actual scores on ebay, not necessarily about subterfuge, but I gather, more about avoiding confusion from different testing methods, tube testers used, and having had trouble with buyers over differences from different testers...different calibration, etc. So if you see words like this: "These are used tubes testing very strong, balanced and are dead quiet tubes" it would seem the tubes "test strong" means they have a lot of life left in them, the measurements hopefully comparing closely to NOS....are "balanced," meaning the triodes balance well....and are "dead quiet," meaning they are tested for noise also. In these cases, if they do not post test numbers, I ask the seller for the test scores to verify, but this explanation puts us on a good track.

Or you may see something like this: "Selected for match between the two halves and the two valves within 5%" also potentially very good match, but perhaps best to verify numbers also.

For pairs, I also look for the same construction, and dates. If everything matches pretty well electronically, and the tubes are the same (or close enough production for matching design, materials, vintage....), seems chances of better performance as a pair are higher.
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