Where would one go to to test old tubes to see if they are still good?

[Nick Athanasatos]

I have the Sylvania STR415 6L6 tubes that came with the MkIIC I got from original owner.He changed them with new 6L6 Boogie Tubes from the Mesa Boogie store in California I think, he said figuring they were old and needed changing.
What's the story with these old tubes on eBay labeled as refurbished ?
And where would one buy a new set of those Sylvania Tubes from a reliable place ?
And what would a matched set of 4 cost ? Thanks

 

[user 84685]

You cannot refurbish a valve. It is a glass envelope with the internals withing an almost perfect vacuum.
Clean them on the outside, if you are careful maybe but that is not refurbishing.
A misleading advertisment in my mind.

NOS or New Old Stock is less of a gamble, bearing in mind, if they are as described, they can be rejects that did not sell when made.
I always test new stock with my AVO CT-160 to check the parrameters.

 

[Stinger22]

I made the effort to find a tube testing machine in my area a couple of years ago to no avail. When I was a teen working at the corner drug store we had one and I helped people ID their tubes and test. The cabinet part was filled with various tubes we stocked. Sure wish I had those now! The machines were pretty common back then.

You can find stuff online for simple testing with a multi meter.

 

[user 84685]

Unfortunately, one can only measre continuity of the heaters with a meter unless the valve is plugged into a test bed, then the anode current at a known grid voltage can be measured.
My AVO sell on fleabay for around £1600!

 

[Rbh]

I would advise against buying used power tubes unless they're described as new-"ish" lol - or the seller gives some kind of assurance for return if they're bad. I've bought used power and Pre-amp tubes a couple of times and never got burned. If you can find a music store that does in house repairs - They likely have a tube tester. I recently measured all tubes for a simulclass 295 from 87 - 89 years. I brother owned the amp originally. I know it had very low hours on it. All tested consistently. It takes a couple minutes each to test, so expect to pay a little bit. I'm lucky that we have an " real" electronics store and repair shop in town as well.

 

[woodbutcher65]

Get a GOOD tube tester that has been well maintained and send it to a specialist who rebuilds and recalibrates them. Then you can test tubes yourself.
My slightly modded B&K 707 tells me almost everything about a tube that I want to know. If it also includes noise figure measurements, it'd be perfect. But no stock tube tester includes that.

 

[user 84685]

After testing the valve on my AVO, I designed and built this handy noise testing devive. It allows for the biro test as well to check for microphonics.
Very usefull and took about an hour with a small blank chassis to make. Component values are nominal.
Plug it into a test amplifier and adjust its gain accordingly.
Very simple.

 

[Janglin_Jack]

As already noted, a tube tester is a good way. It would probably be easier to find a tube amp repair person in your area and ask them/pay them to test your tubes. If you opt to buy a tester good ones are costly. Vintage ones can be had, but they could have issues and will likely need to be calibrated. All of this takes time, money and some amp repair knowledge. I would avoid tubes labeled as refurbished. Fixing a loose base or something similar I can see, I just don't know what/how they are refurbing a tube Seems like you would have to remanufacture a tube and who has a tube factory in their garage. It is a vacuum tube and not really serviceable. All that said, I got a Hickock tube tester and tested all my tubes. I found a couple weak power tubes and a couple rectifiers tested weak from a 1940's phonograph/stereo consol that were bad. I maybe had 3 bad preamp tubes out of 100 or more. I was surprised at how reliable all my tubes were as over 95% tested reliable. I had fun buying a tester and testing the circuit and calibrating, etc. I don't know that everyone would get joy out of this process and doubtful it is cost effective.

Good luck.
Mike

 

[JerichoKing]

After testing the valve on my AVO, I designed and built this handy noise testing devive. It allows for the biro test as well to check for microphonics.
Very usefull and took about an hour with a small blank chassis to make. Component values are nominal.
Plug it into a test amplifier and adjust its gain accordingly.
Very simple.

This is awesome, Jon!

A video demonstration on how this works would be invaluable. Also, any interest in making this for folks who don’t have a lot of confidence in this realm?

 

[StratExpress]

Do you have an amp that can take the tubes. Best test is your own ears in my opinion!

 

[Theresa]

Testing tubes require to test for shorts, leakage, mechanical failures (microphonics) plate and grid current draws, anticipated life left on a given tube. To test a "go, no go" is folly. (Like the ones you used to test at the 7-11 stores). This is an example of my Hickok 800A Tester.

 

[xdg999]

I own the Maxi - Matcher 2 and the Maxi - Preamp 2 testers. I'll test your tubes for free if you live in the Chicago area.

 

[Nandrewjackson]

The answer is obvious,

 

[bandit2013]

I do the floor drop test once in a while. If it bounces back without breaking it may still be good.

 

[philster]

You cannot refurbish a valve. It is a glass envelope with the internals withing an almost perfect vacuum.
Clean them on the outside, if you are careful maybe but that is not refurbishing.

I recently acquired a quad of EL34s one of which tested dud (heater open circuit). I scrubbed the pins with DeOxit and it brought the EL34 back. The pins looked allright, and I couldn't believe the dirt that came off the pins after leaving some DeOxit Red on them for a few minutes. Just shows that these things do over time attract dust and grime which can impact their performance all the way to failure.

I reckon I 'refurbished' that tube good and proper.

On another note, I built this tube tester and use it to validate / match tubes now. It ain't pretty, but sure does the job.



Detailed design and instructions here: A low cost, easy to build diy valve/tube tester | Valve Heaven

Big shout-out to Grant who is incredible and still actively responding to comments (over 800 so far!) and helping builders with their questions.

Once tubes are measured and matched, the final test is in the amp. Warm it up, play it, if it sounds good, it's good. In doubt, tap the tubes with a chopstick to see if microphonic.

 

[user 41014]

I recently acquired a quad of EL34s one of which tested dud (heater open circuit). I scrubbed the pins with DeOxit and it brought the EL34 back. The pins looked allright, and I couldn't believe the dirt that came off the pins after leaving some DeOxit Red on them for a few minutes. Just shows that these things do over time attract dust and grime which can impact their performance all the way to failure.

I reckon I 'refurbished' that tube good and proper.

On another note, I built this tube tester and use it to validate / match tubes now. It ain't pretty, but sure does the job.

View attachment 1676

Detailed design and instructions here: A low cost, easy to build diy valve/tube tester | Valve Heaven

Big shout-out to Grant who is incredible and still actively responding to comments (over 800 so far!) and helping builders with their questions.

Once tubes are measured and matched, the final test is in the amp. Warm it up, play it, if it sounds good, it's good. In doubt, tap the tubes with a chopstick to see if microphonic.

Thank you for sharing. This is on the to do list to finally have a tube tester.

 

[Sinner's Swing!]

If he replaced the tubes, why not just keep the old ones as spares? If the new tubes go out, you can use the old set of Sylvanias until you replace with a matched set.

 

[Fiveband]

The MaxiMatcher allows you to test power tubes at 400V. The Maxi also tests current draw. You can get a very good match with this tool.

The older tube testers, like the Hickok test at much lower voltages, and will not give as good of a picture of the tube as you want to use it in an amp.