Tube Lab

[@RickO.-vq8oh]

Best tube trick I learned years ago - if writing is worn off, you can put tube in freezer for 30 minutes and when you take it out, the original writing will show up as the glass starts to warm. Also you want to watch for cathode metal plating out on the glass from years of cooking - good sign of a tube that has been worn out.

[@tubelab194]

@@RickO.-vq8oh great tips for everyone, thanks!

[@slaquers]

great tip, im gonna try this on some

[@mikerca]

An old timer told me back in the 70s, if you can’t see the tube designation, just breath with an open mouth onto the tube and you can then see the tube number in your moist breath on the tube. It always worked for me.

[@jeffreyyoung4104]

@@mikerca An old tech showed me this trick in the 60s, and there have been very few tubes that had no markings because of windex. If a tube is dusty and dirty, and it doesn't just blow clean, use care, as most of the writing will come off and the value of the tube will go down.

[@stillbobrb9]

I rarely buy tubes but occasionally I will buy what I need- mostly generally signal or amp tubes. I was given a bunch of tubes and recently I went through and found most tested good. The original owner repaired televisions in the 50s and 60s. I noticed on eBay sellers are selling untested tubes, don’t know if any of them are any good-I won’t buy them. Some sellers on eBay will make offers-that to me send red flags. I enjoy your video.

[@itsonlyme9938]

I saw some vendor selling his farther,s valve collection one was supposed to a GZ32 with original box and this example had a anode cap on it. Not a clue what he was selling. It does make me wonder when I see vintage valves being sold as new old stock with the original box as to weather the new valve has been taken out and used and the old one put back into the original box as a spare because it still has some life left in it ?

[@tubelab194]

@@itsonlyme9938 that happened a lot, but you can easily determine if a tube has some hours on it, by checking the gettering, pins, base and of course the testing numbers. Now because many vintage tubes are now 60-80 years old, even brand new, never opened boxes will have tubes that look like they've been riding the back seat of a dirt bike for an afternoon. Those tubes mostly just need a good clean-up, in particular the pins, which will be oxidized and of course tested properly.

[@gearheadted9210]

cheers guys just about finished with a bk747 hope to be doing buisness soon 40yrs in automotive is plenty !

[@TomSherwood-z5l]

I have only had one tube deal bad, a seller with an accent sold me a dud balloon tube that was not the one in the photo on ebay. Frankly I buy from a reputable dealer with a website in northern Ohio. His prices are nearly always better than the gougers on ebay and he is reliable. He sells tested used or NIB. I have sold some tubes online in the past, I used my TV-7 to rate them. I got a HIckok but what if I say a tube tests on Hickok 3500 and his says 3450, he will be upset. TV-7 is good and no one has objected to it's values.

[@pibbles-a-plenty1105]

Gentlemen, having noted your difficulty in describing what tube testers do, let me help: You probably already know that the TV-7 series of military service tube testers is a trans-conductance (mutual conductance) tester designed and patented by Hickok, which uses AC control grid drive and measures AC plate voltage response. That type of circuit is simplest to apply operating conditions to a tube under test and gives the most accurate plate response readings translated into a trans-conductance reading value. An honest tube seller should be quoting the readings from a trans-conductance measuring tester that he routinely uses that is properly calibrated. If the seller does not demonstrate his capability as part of his sales appeal you should think twice before buying. On average, in my experience, the most reliable sellers are on eBay because of eBay's buyer protection procedures. FWIW.

[@tubelab194]

I don't recall having any trouble talking about what tube testers do. And given we have about a dozen of them, many rebuilt by us and one Custom Power Tube Tester/Matcher substantially designed and built by us, I would consider us at the very least experienced professional operators of said Testers. But your point about looking for Sellers that declare the type of Tester used and the testing numbers is an excellent way of sorting out the good from the bad. In our experience a better approach (one we use everyday) is to purchase from known good Sellers, who know what our expectations are (high) and sort/price accordingly. As a result we often pay slightly higher prices from our wholesalers - BUT we almost always get the very best tubes they have to offer. They then sell the leftover tubes on ebay!

[@Luckiestmanalive-bb1mi]

Thanks, for your tips and caution around dodgy tube sellers and their practices. I'm relatively new to tubes (couple of years) and I've learned the hard way the tricks that online sellers use to get noobs to part with more cash and move their stock. The classic is to sell the tubes as untested when the seller knows full well they are unmatched and/or weak. The other gotcha I've found is that you must buy matched pairs or quads from sellers offering them or you are almost certain to get very unmatched tubes (they are the ones at either extremes). I bought two matched pairs of KT120s and, of course, one pair was marked 76mA and the other was marked 84mA. I have become so suspicious of sellers I am not interested in tube rolling anymore. I have a good combo for my PP amp and will keep them until they fail.

[@tubelab194]

@@Luckiestmanalive-bb1mi yup! Note we automatically match pairs/quads at no additional cost. And your KT120's at 76 and 84mA are actually close enough to call matched, though at the limit (10%) of what I would consider acceptable.

[@Luckiestmanalive-bb1mi]

@@tubelab194 - thanks! The seller wasn't offering quads so I was hoping they might have been a little more generous!

[@TomSherwood-z5l]

The world is awash in dud tube stashes. I am amazed how many people used to save weak or bad tubes and even put them in boxes rather than toss them. Anything the tube does not match the box, is likely an issue. Or a dirty tube in a clean box. The lots of loose tubes I find consist of duds or very weak mixed with good or very good. Makes no sense.

[@tubelab194]

@@TomSherwood-z5l "back in the day" many repairmen had only a rudimentary understanding of how to troubleshoot a circuit, so their standard procedure was to replace the tubes one at a time (or all at once) and see if that fixed the problem (it often did). Then they would stick the pulls into the new boxes and plan to test them at some later date. Often that never happened and well you know the rest of the story!

[@2tallB]

That “untested “ claim is so common (for any vintage electronic gear) - then you look at their other auctions and see lots of similar gear so it’s unlikely that they can’t test it. Or sometimes you even see a bench with equipment that makes it even more suspicious.

[@bertroost1675]

I got a lot of good tubes (for example maybe two-hundred 6080 tubes) from an old military surplus shop closing down. I am afraid to sell them on ebay because I feel someone will say the tube was bad and send me back another one.

[@tubelab194]

@@bertroost1675 if you properly test for "idle plate current" and only sell NOS (new old stock) or very nice used tubes, then you should be fine.

[@josepheccles9341]

Those 3 tubes are 6N9P. I buy those from time to time.

[@TheWarped45]

Oh yes I have a tv-2 with the roll chart.

[@revelry1969]

Are those KT88 on website?

[@TomSherwood-z5l]

i had a red base Raytheon for years from a loose tube lot with no mate, recently I found another in a garage sale loose tube box, now they are tested and a good pair.

[@tubelab194]

@@revelry1969 Yes here's a LINK: valvesnmore.com/?product=kt88-tubes

[@dyamariv3628]

Your website link doesn't work, is there an issue with your site?

[@tubelab194]

No it's always live. Just Google valvesNmore and it will pop up on top.

[@giulioluzzardi7632]

70% of Valve amps in use today use Russian made valves. The "Cold War" caused a bias against Eastern block manufacturers. The fact is most of the best after the early 80s are Eastern block made. NOS from Europe will sound fantastic but 3 out of 4 will be useless( unless you don't mind super-microphonics). So you buy 4 ecc83s NOS and only 1 will do the job. If you are lucky and have extra cash to burn buy twice as many as you need and test them in the amp, whether V1 or phase inverter. Your ears will let you know if you did good.BTW, who can we turn to for original spec 5881s?

[@tubelab194]

@@giulioluzzardi7632 thanks for contributing. A couple of clarifications from our view point. I would guess the audio tubes in use today, break down something like this (25% vintage, 25% moden Russian 15% E.Europe (JJ) and 35% Chinese). Our experience with Soviet era tubes has been almost 100% positive, for most factories. We definitely don't see many microphonic tubes our of the former USSR. Modern Russian tubes (New Sensor) is a totally different story, with short lived power tubes being the biggest problem and just mediocre sounding tubes. That's not surprising given that many of the Reflector tubes (same plant as New Sensor today) made in Soviet times also aren't very good (some exceptions). That said some New Sensor tubes like their top line Genalex Gold Lion is one of the best 12ax7's ever made (watch out for Chinese copies!).

[@pibbles-a-plenty1105]

Dual triodes in an envelope, in most cases, the two triodes do NOT need to be matched. But of course, both triodes need to test well to perform with low distortion and have a good service life.

[@tubelab194]

In our experience this is patently incorrect when the tube is used in an audio preamplifier or power amplifier. In many cases one half of the dual triode is handling the left channel while the other half is handling the right channel. And in the case of true balanced circuits one half is handling the hot leg and one half the cold leg. In both these examples (and many more) it's critical for good audio to have matched sections across all related tubes in the circuit. Now if you are talking about an instrument amp, for example the input tube of a typical guitar amp is often a 12AX7, in that case so long as the tube is testing good, it's not a requirement to have matched sections. And you could probably come up with a number of circuits in which mismatched sections aren't required. But in general yes, matched sections are a requirement for good audio.

[@Joseph-ut4ui]

I've been a tech for 51 years and this is the 1st time I've heard of the "missing gettering" method of determining a tube performance or life expectancy. I just use one of many Hickok tube testers and have never had a problem. Also, you basically state that not testing a rectifier at full rated voltage will give inaccurate results; IMO, that is not a valid claim. BTW, you show a 5AR4; do you test that at 1500 to 1700 volts per plate? I think not.

[@tubelab194]

@@Joseph-ut4ui Thanks for your comments, but in reviewing them it looks like you didn't fully watch the video. Assessing a tube based on the state of the gettering is just one visual element to take into account, as mentioned we then look at the pins, base and overall condition of the tube. This was mostly for people shopping online, to give them some idea of what they're buying, though we use this method ourselves and it has served us well in thousands of tube purchases. We of course properly test the tube electrically to determine whether it's good for the Store or the bin. When we were talking about Testing voltages, it was specifically about Power Tubes, not rectifiers (though you make a good point, btw our custom Tester can go to 1,000vdc with bias of +/-100vdc). In the resale/wholesale market the single least understood Testing Method is for power tubes. There is only one Industry Standard Test for power tubes and that's the "idle plate current test". I would note this is an open Comments section and is meant for friendly discourse, if you want to be adversarial, this is not the place for it.

[@josepheccles9341]

They make a metal base one that is much better, those are what I have.

[@tubelab194]

@@josepheccles9341 could you please clarify what you just posted. As it stands I have no (zero) idea as to what you are talking about or how it relates to the latest Tube Lab episode on Fraudulent Tube Sellers. Thanks Jim

[@josepheccles9341]

@@tubelab194 The Russian version of the 6SL7 is 6N9P. There is a military version that has a metal base instead of plastic. The military version is a little better sounding tube, but aside from the base they look exactly the same. Also, there is a version of 6SN7 it is 6N8P, it also has a military version that has a metal base. I think they are just graded and the better ones are saved for military use.

[@tubelab194]

@@josepheccles9341 are you referring to the Melz 6H9C/6N9S/6SL7GT, many of which have a metal base. As far as I'm aware Reflector never made a metal based 6SL7.

[@josepheccles9341]

@tubelab194 I believe so. But I bought them a few years ago and haven't found them lately. I could only find the plastic base the last time I looked for them. I got the ones I have from either Amazon or ebay.