Tube Rolling w/Crack

[Larpy]

You'll have to let us know how long that took!

I'm embarrassed to admit that the lesson didn't fully sink in until early 2020, after I built my Kaiju and bought my first pair of Western Electric tubes: the 396A ('60s vintage).  At last, I had my hands on fabled Western Electric tubes!  Maybe "fetishized" is a bit hyperbolic, but I was prepared to be sonically transported to a land of audio bliss after I installed them and powered up the Kaiju.

Meh.

That was the straw that broke the camel's back.  Call me a slow learner.

 

[larcenasb]

I just got a new 12AU7 (1950s RCA black plates) that has a faint and constant hiss in the left channel. Switching to other 12AU7s makes the hiss go away. The loudness of the hiss is the same whether the volume knob is turned all the way down or all the way up. When music plays with low volume, I can hear it; with medium-loud volume, I faintly hear it.

Is there a typical cause for this kind of hiss? And is there anything I can do to fix it? Thanks.

 

[Paul Joppa]

I believe it's usually in the cathode coating, either interface resistance or the cathode is not fully formed. In the latter case, it may go away with the usual 50-100 hours running time. If it's interface, it's a used tube and won't go away.

 

[larcenasb]

The tube tested 82/80 on a "calibrated Precision 612 vacuum tube tester" where the minimum reading is 46/46. The seller didn't say what a typical new tube would test at, but looking at photos online shows this tester's scale goes up to 100. So, I guess it's a used tube?

But since the tube was just a few dollars, rather than return it, I'll use the opportunity to learn and see if "the cathode is not fully formed." I'll run it for 100 hours and see if the hiss goes away. Thanks, Paul. Always great to hear from you. Cheers

 

[Paul Birkeland]

I have a precision 612.  80 is typically considered the lowest rating you would expect for a new tube.  I've had brand new 12AU7s fresh from sealed boxes only read 80 on the meter, and I've had used Russian 12AU7s peg the meter, so there isn't really much information there beyond there being adequate emission.

 

[larcenasb]

Thanks PB! Always nice to hear from you too! So, hopefully, the tube is new or newish and the cathode is not fully formed. I'm excited for this test, running it for 100 hours to see what happens. I'll report back. Cheers

 

[Doc B]

Larpy is the most excellent voice of reason here. I agree 110%. Re the last two posts, the same historical inflation due to necroposts about "what's best" goes for tube testers. I bought my TV-10 D/U in 1991 for $50. I've sold testers for $750 in more recent years. The very best tube tester is the device you intend to run the tube in, so I wouldn't be too concerned about "80%" etc.

 

[larcenasb]

Here's an update on that 12AU7 I got that had the constant hiss in the left channel. After just 2 hours of running them, the hiss volume went quite low. If it was 6/10 before, it then went down to 2/10. After 3 hours, the left channel started crackling. There would be the slight hiss then a couple seconds of crackle-crackle-crackle, then just slight hiss again, then more crackles. The crackles are like rice crispies and aluminum foil being crumpled in front of my ear. At this point, I turned off my amp and came to check in. Is it safe to keep running the amp, to try and see if the hiss will go away, if there are crackles? Is the tube dying? Thanks so much.

 

[Paul Birkeland]

Crackle is more of what we would expect from oxidized tube pins or possibly a solder joint that isn't quite 100%. 

You can clean the tube pins gently with steel wool and you may find that crackling goes away, just be sure you get any loose fibers off the pins when you're finished. 

 

[monsterdonkey]

It’s funny. I was reading this thread about a 12AU7 that hisses and I have one of those. It’s a modern Northern Electric 12AU7. Some people review them favourably so I added one to an order of vintage tubes I bought a couple years ago. It was the most expensive and also the worst sounding of the bunch, or so I thought. It hissed loudly enough that I never used it. I just went to set the Crack up in a corner to let it burn in this hissy tube, but I plugged in a GE 6080 I haven’t been getting along with that well so as not to put unnecessary hours on a tube I enjoy. A quick check on the headphones to see how it’s sounding at the beginning of the experiment and the hiss is missing. Could it be that it had a reaction with my other preferred tubes? Maybe whatever I don’t like about the GE 6080 also happens to defeat the hiss noise? Maybe my ears are that much worse since I last tried that tube? Who knows?

Edit: oh wait, there’s a 60Hz hum or something there too.. I’ll let it run all day today but after that I’m done with that tube. I can’t see the point of messing around with it when there are plenty of very good cheap tubes around, several of which I already own. I can accept that sometimes you get a dud. Maybe it could work in a guitar amp.

 

[larcenasb]

Thanks Paul & monsterdonkey.

Paul, this is the only tube I have (of many) that exhibits crackling sounds, so I'm hoping my solder joints are all good (my Crack has been running perfectly since 2014). I cleaned the tube pins with steel wool and the crackling went away!

So, I'm continuing running the tube for 100 hours. About 9 hours in now, the hiss sound in the left channel is very low. It's now at 1.5/10. Will update after 50 hours. Thanks again for your help.

 

[larcenasb]

Update on 12AU7 left-channel hiss:

So, to recap, after 2 hours the hiss volume decreased and there was a short episode of crackling. Cleaning the tube pins seemed to fix the crackles.

Now, the hiss has been a consistently low volume. But after 25 hours, the hiss started gradually getting louder (lasted about 10 seconds), then some crackling occurred (lasted 5 seconds), then the crackles went away and the hiss went back to the earlier low volume. This was all just in the left channel; the right channel has no problems.

Are these new details indicative of anything in particular, just a bad tube maybe?

 

[Tom-s]

Do voltage checks with that tube. Let us know. These can help pinpoint the problem.

 

[Paul Birkeland]

Have you left the amp on since the 19th? 

 

[larcenasb]

Hi Tom-s, I can try to do the voltage checks this weekend.

Hi Paul, I was home all day on the 19th and 20th, so ran it for 24 hours. Besides that, I've just been running it when I can.

Here's my log:

9/18 - 2 hours
9/19 - 24 hours
9/22 - 5 hours
9/24 - 3 hours

Total so far: 34 hours

 

[Paul Birkeland]

OK.  Turn it on now, then leave it on till Tuesday and let us know how the noise is after that.

 

[larcenasb]

Alright, will report back on Tuesday. Thanks, Paul.

 

[larcenasb]

Update: Ran the amp nonstop from Friday to Tuesday and the hiss is still present along with intermittent buzzing. I then switched to another tube and no problems at all. So, I just got a noisy tube it seems? Nothing can be done to fix it?

 

[Paul Birkeland]

That could indeed be the case.  Occasionally you'll get a tube that's more sensitive to external interference for one reason or another and a different tube won't pick up any noise.

 

[larcenasb]

Alright, it was still a good experience of troubleshooting and learning. Now time to enjoy my 6F8G tubes via an adapter. Cheers and thanks for your help, Paul.