|waspclothes||5/18/2017 10:32 PM|
|Selling tubes on ebay - how to describe their working condition properly?|
A buddy of mine showed up with a few boxes of old tubes he's kept from the last 40 years of playing guitar. Some were old power tubes that were clearly very used, but he also had about 30 12AX7's that saw little use according to him.
He wanted me to "test them" so he could sell them on ebay, and I'd like to help the dude get some dough for this stuff. I don't have a tube tester, and I told him that I test tubes in-circuit. My non-scientific approach basically just has me saying "yes, this 12AX7 works" but that sort of description probably isn't going to get this guy a lot of bids.
I see a lot of ebay tube auctions show the results from Hickok tube testers as a de-facto standard, but is there anything I can do with an amp, scope, generator and multimeter for this guy that's better than "tube works"?
If I measure the AC input, should I expect to see an AC output 100x the amplitude for each triode in a 12AX7 for example?
|Enzo||5/19/2017 12:23 AM|
|You plug your 12AX7s into a working amp, one by one, into the same socket. Play something consistent through the amp, like one song on a CD. Set the controls once for a comfortable tone and level and then don't touch them. If the tube works, keep it. If the tube shows some trouble, like noise or low output, toss it. |
Frankly I wouldn't pay much for contemporary 12AX7s used. If they were old RCAs or GEs or Sylvanias, maybe a little.
Have you looked on ebay to see what used tubes are selling for? Tubes of the sort you have that is. A used black plate RCA 6L6 has value, but I don't expect to see folks selling used Sovteks. I could be wrong.
|Randall||5/19/2017 12:40 AM|
|Tell him to forget it. Anything that is not USA is not worth the trouble, considering shipping costs. Anything that is USA may or not be worth the trouble, but on the whole will be a waste of time, unless there is a nugget like nice old working pair of RCAs, in which case, keep them.|
|Mick Bailey||5/19/2017 1:07 AM|
Maybe these don't fetch money in the USA, but elsewhere they fetch a strong price. I've even sent Mullards and Telefunkens to Vietnam.
Regarding testing, a 12AX7 will not provide a gain of 100x in a tube amp circuit. Audibly, gain variation has to be considerable to make any real difference. Those tube-tested 12AX7s can be noisy - I have 5 JAN Phillips that test fine but sound like rustling paper in an amp. A tube tester is not a 100% reliable means of establishing a tube is good in an amp.
My test is firstly to hold the tube between thumb (pins) and forefinger (pip) close to my ear and lightly tap it with the back of my other fingernail. Those that rattle and sound loose get put to one side as suspicious for microphonics. Then I then put them in an amp, one by one, and do what Enzo suggests. I find that a higher-gain position can expose noise problems best. I tap the tube in-circuit to make sure it has low microphonics, and listen for any noise. You need to let the tube warm up thoroughly as sometimes noise only becomes evident after a few minutes.
Noise and microphonics would be the main reason for rejecting a tube. And, of course, if the heater is O/C or the tube is shorted.
|Enzo||5/19/2017 1:04 PM|
|I think by not USA, Randall meant the same thing I did, namely Chinese, JJs, Sovtek, and other cheap present day product. A fine old Mullard 12AX7 might be fun to have, a used current "Mullard" from Sovtek, not so much.|
|waspclothes||5/19/2017 2:46 PM|
|Leo_Gnardo||5/19/2017 3:09 PM|
Reverb.com another potential sales venue. AFAIK it's not an auction site. Just post your price & you may get hits. And there's always our own MEF Flea Market. Price 'em cheap enough and they'll move.
|Mick Bailey||5/20/2017 2:09 AM|
|The prices I've got for old tubes can be eye-watering, especially old Mullard ECC83. The most sought-after are from the Blackburn factory. Look at the etched codes and you'll see the factory location - find the list on the web.|
I regard those tubes as 'forever'. I have pulls from old 60s tape recorders and radiogram consoles that beat any current-production tubes. The pins go a little blue and need gently cleaning, but they last and last. Just take care when handling them - the printed logo rubs off very easily.
Mullard sold 'white label' tubes to re-branders. You can get Mullards branded up as 'Zaerix' and others. The clue is in the etched code.
An interesting clip about the Blackburn factory and manufacturing;
|waspclothes||5/23/2017 5:43 PM|