Tube Rolling w/Crack

[Colonl_Charisma]

I've been using the Thomson 6080WA for a few months now in my Crack. No issues to report, and I definitely did not do anything special to it. Just popped it in haha.

 

[cddc]

There have definitely been a lot of posts about people having problems with that particular seller, so take that for what it's worth.  That seller also doesn't understand that a directly heated rectifier will put out full voltage within a couple of seconds after being powered on, so even that statement is a little peculiar.

Wow, there are even directly heated rectifier tubes, first time to hear it  ;D I thought there are only directly heated power tubes, like 300B or 2A3.

But that seller's comments on needing a soft start from tube rectifiers also confused me, why would a 'hard' start prevent Thomson 6080WA from performing? It just doesn't make sense to me.

 

[mcandmar]

There have definitely been a lot of posts about people having problems with that particular seller, so take that for what it's worth.  That seller also doesn't understand that a directly heated rectifier will put out full voltage within a couple of seconds after being powered on, so even that statement is a little peculiar.

I wonder if those tubes were more susceptible to arcing on start up.  I know of a certain "Chinese made" amplifier with 6080s that has a daft 3000uf of capacitance in the power supply, maybe they didn't get along.

 

[Paul Joppa]

...

But that seller's comments on needing a soft start from tube rectifiers also confused me, why would a 'hard' start prevent Thomson 6080WA from performing? It just doesn't make sense to me.

The 6080 can draw excessive current - enough to damage the cathode - if the cathode warms up before the bias kicks in. There is a warning about that in the data sheet, including a minimum cathode bias resistance.

In Crack, the 6080 is operated as a cathode follower, and has a 3000 ohm cathode resistor - about ten times greater than the minimum.

 

[cddc]

Thanks PJ, I've never noticed that warning in tube data sheet (at least not in the RCA 6080 data sheet that I have).

Is this a specific problem to the Thomson 6080WA tube? Or the seller is selling duds?

I've never heard such problem on other 6080/6AS7G family tubes. Also, you mentioned the cathode resistor in Crack is large enough to shield the impact.

 

[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  ;D

 

[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  ;D

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.  ;D

 

[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.