Tube Problems from Tube Depot

[Thisismyname]

My go-to parts store, mostly because of their resistor selection and shipping times.

I've gotten some bad 6L6s this summer. First was a pair of JJs, one was microphonic outta the box. Returned, and bought a pair of Sovtek 6L6WXT+. These have a special construction to minimize microphonics.  Sound better than the JJs, which are too sterile and cold IMHO

After about 10 hours, one starts to go bad. Internal shorts I'm assuming, excessively high bias on the one, thumping noises that correlate with significant fluctuations of plate voltage and current.

Returned, got a replacement today. One is microphonic outta the box. I can hear it ring when tapping on the chassis. Build to minimize microphonics and it's still microphonic. I'm getting frustrated. It's not even my amp. I don't know how these microphonic tubes slip past QC at Tube Depot, or what it could be.

Is my best option to just keep returning them and hope that I'll eventually get a pair that's not microphonic? Or should I try a different site?

[HotBluePlates]

Is my best option to just keep returning them and hope that I'll eventually get a pair that's not microphonic? ...

Yes, that's your only real option.

... should I try a different site?

You can, but you better be certain they have a solid return policy.  Every currently available brand has been the "shoddy brand" at some point, so they'll all be problematic eventually.  Your only protection is the ability to return for a replacement (that hopefully is problem-free).

[shooter]

excessively high bias on the one

do you bias any new tubes you put in?


I like to keep a "test set", take out old tubes, put in test set, bias, monitor while playing, amp stable? yes;  pull test tubes, add "new tubes", repeat.
this will "catch" induced oddities like broke a solder joint wiggling the 'ol tubes out, sloppy socket cups, bias pot sketchy....
 

[dogburn]

Since Sovtek tubes are made in Russia and presumably not currently being imported due to the war, so supply is limited. Maybe different sellers are down to selling their iffy stock of Sovteks?

[Thisismyname]

excessively high bias on the one

do you bias any new tubes you put in?


I like to keep a "test set", take out old tubes, put in test set, bias, monitor while playing, amp stable? yes;  pull test tubes, add "new tubes", repeat.
this will "catch" induced oddities like broke a solder joint wiggling the 'ol tubes out, sloppy socket cups, bias pot sketchy....

Ya, I bias all my power tubes at 70% unless cathode biased. I do have a test set of JJs that I use.

One tube was biasing fine at 18w, the bad one was 24w and slowly climbing.

[pdf64]

… I bias all my power tubes at 70% unless cathode biased. I do have a test set of JJs that I use.
 …

Although ’idle fixed bias at 70%’ has become received wisdom, it may be much hotter than Fender ever intended for 6L6.

If 6L6 triode curves are used to derive idle anode current for eg the -44V bias @ 420V screen of the aa864 Bassman, end up with about 20mA.
https://tubedata.altanatubes.com.br/sheets/093/6/6L6GC.pdf
https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_aa864.pdf

Try the process on the Fender model of your choice, they all tend to work out about the same.

 A couple more points.
1 to avoid the chance of them running super hot on existing bias setting, when initially fitting new valves, before powering them up, set bias as cold as possible. Then adjust as required.

2 use a light bulb limiter when initially powering the amp up with new / unknown rectifier or output valves. Bulb about twice ghe wattage of the amps clean audio power output rating. Once they’ve proved that they’re not likely to short out, get rid of the the limiter before setting bias etc.


Broken links fixed -- HBP

[BrianS]

I only buy new tubes from Amplified Parts.  They seem to have the best matching and "burn-in" processes currently available.  I can't recall getting a bad tube from them.  Not saying it doesn't happen, but they seem to have the best quality control around.

I no longer purchase Russian made tubes, and I've never purchased Chinese tubes, so that leaves JJ.  Amplified Parts offers some JJ sets as "Apex Matched, Burned-In", which is what I buy when it's available as an option.  I've spoken to them on the phone about this and it's essentially an extra step taken to weed out a few more tubes that will go bad sooner rather than later.

[Latole]

I sometimes have some tubes's problem at The Tubes Store.
These guys are honest and the replace the bad tube.

[Carlsoti]

I only buy new tubes from Amplified Parts.  They seem to have the best matching and "burn-in" processes currently available.  I can't recall getting a bad tube from them.  Not saying it doesn't happen, but they seem to have the best quality control around.

I no longer purchase Russian made tubes, and I've never purchased Chinese tubes, so that leaves JJ.  Amplified Parts offers some JJ sets as "Apex Matched, Burned-In", which is what I buy when it's available as an option.  I've spoken to them on the phone about this and it's essentially an extra step taken to weed out a few more tubes that will go bad sooner rather than later.

I agree. I've had ONE (oddball pre-amp) tube from them that wouldn't work in the circuit on my bench. Called and asked about it. They said it was tested and passed, but I'm more than welcome to bring it back and swap it for another. The replacement tube worked fine without any other changes. It helps that I'm local and didn't have to pay to send it back, but CE Dist/Amplified Parts/ Antique Electronic Supply seems to have a good reputation for standing behind their work when it comes to matching and testing tubes. It's always the first place I look when I need a few parts for a repair, or reliable new-production tubes.

[AlNewman]

I sometimes have some tubes's problem at The Tubes Store.
These guys are honest and the replace the bad tube.

I bought a couple 6at6's a few months ago from the tube store, along with some other tubes.  1 works really well, the other didn't conduct, though the heater was working.  It's a 10 dollar tube, i probably won't send it back, but it's nice to know I could.  They seem very professional, with return options if necessary.  Canadian options for duties and shipping is always what I'm looking for.