Are we all stupid

[jestaudio]

Bit of a odd title granted but it stems from a conversation I recently had with a amp tech, I sent in a bunch of amp pulls to be tested, mix of Mazda and Brimar ecc83s and some el34,s and el 84s, didn't here anything for a week so made a phone call, asked how they looked and was told they are all scrap, not what I expected, so I asked for the test results, 90% had passed on test so why are they scrap. Apparently those that like NOS tubes or even vintage tubes are all thick as pig doo doo , any tube over 5 years old is scrap etc etc etc. Needless to say I have reclaimed my tubes, paid for the testing and will be finding another person with a test rig.

Now I don't claim to be a great authority on tubes but I'm pretty sure that decent NOS generally sound better than modern stuff, at least to my ears and my attitude certainly with preamps is if it ain't broken don't fix it, it sounds to me like a bit of a scam to be honest, after all why would you throw perfectly good tubes away

[billyz]

My instincts tell me either he is Ill informed , does not know tubes or possibly hoped you toss them (in his pile).
What tester did he use? Was his tester in good condition and calibrated.
Was he trying to sell you new tubes?
I have used many old 12ax7's that test low but sound fine. The final test for me is always in the amp. I find a tester (tv7/du) is best for finding shorts or bad tubes ( I get very strange readings like needle does not move) . It will test for noise if I use the headphones , but I use the amp for that.

Plug them into v1 of an express and listen. Or the amp of your choice.

[The New Steve H]

I am, in fact, stupid, but I would not throw out a working tube.

[Cliff Schecht]

My instincts tell me either he is Ill informed , does not know tubes or possibly hoped you toss them (in his pile).
What tester did he use? Was his tester in good condition and calibrated.
Was he trying to sell you new tubes?
I have used many old 12ax7's that test low but sound fine. The final test for me is always in the amp. I find a tester (tv7/du) is best for finding shorts or bad tubes ( I get very strange readings like needle does not move) . It will test for noise if I use the headphones , but I use the amp for that.

Plug them into v1 of an express and listen. Or the amp of your choice.

THIS! I usually have a few high gain Champ's kicking around that are great for testing 12AX7's and 6V6's. The more tubes your circuit has, the less you'll be able to hear that one tubes influence, so stupid simple circuits are the way to go for testing tubes.

[Blackburn]

My instincts tell me either he is Ill informed , does not know tubes or possibly hoped you toss them (in his pile).
What tester did he use? Was his tester in good condition and calibrated.
Was he trying to sell you new tubes?
I have used many old 12ax7's that test low but sound fine. The final test for me is always in the amp. I find a tester (tv7/du) is best for finding shorts or bad tubes ( I get very strange readings like needle does not move) . It will test for noise if I use the headphones , but I use the amp for that.

Plug them into v1 of an express and listen. Or the amp of your choice.

THIS! I usually have a few high gain Champ's kicking around that are great for testing 12AX7's and 6V6's. The more tubes your circuit has, the less you'll be able to hear that one tubes influence, so stupid simple circuits are the way to go for testing tubes.

+1000!!!

I feel the exact same way about hearing a tube's true nature in an amp like that. Same thing with other components, but tubes really show their true colors.

[jestaudio]

My instincts tell me either he is Ill informed , does not know tubes or possibly hoped you toss them (in his pile).
What tester did he use? Was his tester in good condition and calibrated.
Was he trying to sell you new tubes?
I have used many old 12ax7's that test low but sound fine. The final test for me is always in the amp. I find a tester (tv7/du) is best for finding shorts or bad tubes ( I get very strange readings like needle does not move) . It will test for noise if I use the headphones , but I use the amp for that.

Plug them into v1 of an express and listen. Or the amp of your choice.

I think he would love to sell me new tubes, especially at his prices lol, I use Watford Valves normally as they are cheap and I only get the odd failure, I can understand to a degree with power valves and I tend to change mine every 20-30 hours in my Mesa but I cannot remember the last time I had a preamp go faulty yet his advice is to change them irrespective after 5 years max, how many folk get huge amounts of time on valves these days any way, I pity the poor bedroom rocker who takes his amp in for a service and gets conned into unnesecersy valve changes

[NickC]

I'm beginning to think that some amp techs are about as crooked as many car mechanics.

[lord preset]

I always make sure to throw out any tubes that have passed the expiration date printed on every tube. Does anyone know what date 5u4gb is?

[Cantplay]

Be especially careful of tubes with military designation.

These weaponized tubes are extremely dangerous.

If they are sent here I can safely dispose of them for a minimal fee.

John

[Phil_S]

...after all why would you throw perfectly good tubes away

Well, I wouldn't and it seems you wouldn't either. Its pretty obvious he was hoping you'd do exactly that, and into his trash...uhh...parts bin.

[RWood]

Be especially careful of tubes with military designation.

These weaponized tubes are extremely dangerous.

If they are sent here I can safely dispose of them for a minimal fee.

John

I'll do it free as a public service!

[gingertube]

Obviously not quite as stupid as that amp tech had hoped.

Recently did a restore of a 60's copper front panel Vox AC30 for a local guy.
The original 50 years old Mullard 12AX7s all tested at about 85 to 90% of new"book" value with rspect to their gm (on my AVO MK3).

Not even for an instant did I contemplate changing them.

I've got 1930's and 1940's tubes in the "stash" which are perfect. How do I know - coz' they went thru the tube tester and all their bretheren which failed the tests went in the bin.

In the final instance, however, you have to just plug them in and listen to them. Use the tube tester to weed out the obvious duds (and those which may damage your circuit if plugged in) but no amount of testing will remove that final "listen to it" requirement.

Cheers,
Ian

[Jana]

I was dropped on my head when I was little. Does that count?

[armillary]

I suspect that modern tubes from second world countries like Russia and China are mostly trash, and that those who would choose them over NOS or used-but-good American and European originals are missing out. Fortunately it keeps the cost of old tubes relatively low, except for the hi-fi cult tubes.

[Stevem]

If you have a amp and even just one known good tube you can test your NOS tubes yourself.
Put the known good tube in the amp drive tha amp with a signal gen and measure the output at each plate with a meter set for AC hooked to the out bound side of the coupling cap.
Write down these two volatges and now pop in your other tubes.
You might find out some interesting things and prove out some interesting things, like this for example.
I have many China made 12AX7B tubes that test out out up to 140% on my Hicok 600 tetser, yet in circuit they did not even match the volatge output of a used GE tube for example that tested out in the high 80s.
Yea, you can not test for shorts of gas, but in the amp you can tap the tube a listen for microphonics, and if you make up a resistor feed for that tube socket you are testing in, you can lower the heater voltage some and test for tiube life.