Tube Rolling w/Crack

[Paul Joppa]

It's common to all 6AS7/6080 tubes.

[Paul Birkeland]

There is a warning about that in the data sheet, including a minimum cathode bias resistance.

It's also worth mentioning that in a Crack with the Speedball, the 6080 isn't able to draw more current than the current sources under the cathode allow. 

[Doc B.]

It strikes me that a failure mode that occurs after just one time running the tube with no visible arcing is likely to be about the tube getting gassy, or having developed a hard short after thermal cycling, or a tube pin connection opening up.

[cddc]

It's also worth mentioning that in a Crack with the Speedball, the 6080 isn't able to draw more current than the current sources under the cathode allow.

Interesting, since Doc B. was talking about arcing and shorting, I am now thinking whether the Speedball will protect us from the possible damages from arcing and short (since Speedball will limit the excessive current draw). haha 

[Paul Birkeland]

Interesting, since Doc B. was talking about arcing and shorting, I am now thinking whether the Speedball will protect us from the possible damages from arcing and short (since Speedball will limit the excessive current draw). haha 

If the grid shorts to the plate, the C4S isn't going to help you.

[cddc]

Thanks PB, then I'll continue to stay away from 5998/421A tubes as they are known to be prone to arcing. 

[Welderboy]

Sigh, so I have another Thomson 6080WA  failure. Second tube, different vendor, same serial number.

Anything I can troubleshoot or is there something wrong with this batch? I don't have a tube tester unfortunately.

In this case the tube lasted several days, and stopped working after I turned the amp off and swapped out a different input tube. Other tubes work just fine, although I do prefer the sound of these.

[Paul Birkeland]

There isn't anything you can troubleshoot if the tube is the issue. 

[Welderboy]

So should I assume there's a bad batch of these being sold? Serial # is FSE-8052-FF in case anyone has one from the same batch.

[Paul Birkeland]

Yes, there are many users positing similar experiences with those tubes from that eBay vendor.

[Deluk]

My Thomson came from Langrex in the UK and is fine and I like the sound with my 4003. This one is from FSE-8140-FF.
Langrex are only about 60 miles from me.

[mcandmar]

Yes, there are many users positing similar experiences with those tubes from that eBay vendor.

The note on their site "Do not use this tube in Chinese made headphone amplifier" is starting to make more sense now, i bet a bunch of D******** owners bought them after reading about them on a forum and had a bunch of failures.  "Do not use this tube in amercian kit headphone amplifiers" will be added next 

[Welderboy]

This wasn't from the .tw vendor - these are two different ones.

[Doc B.]

Sounds like the proper disclaimer is "Do not use this tube, period".

[Paul Birkeland]

Yeah, I wonder what kind of eruptions would happen in an OTL speaker amp, where there are usually no protections in place.