Buzzing noise / 6080 issue?

[tsh]

I built my Crack around 1.5 months ago - was very happy initially, but then noticed that sometimes I have low frequency buzzing noise in the right channel that is loud enough to be heard during the songs. It comes and goes without any obvious reason and does not change when adjusting volume knob position. Sometime it fluctuates slightly up and down in intensity, sometimes just remains at the same level.

What I've done so far as per manual and forum guidance:
- All voltage and resitance checks after the build were within tolerance limits
- Moved Crack away from computers/mobiles/WiFi and tried ipone in airplane mode as a source - the noise is there
- Observed all joints for bad soldering and pulled all internal wires apart from each other as far as possible- the noise persists
- Tested Crack with shortened plugs - the noise is still there
- Finally I've noticed that the noise can be triggered (or if it's already present, stopped) by tapping slightly directly on 6080 tube (not on the aluminium plate). While tapping, I also hear something that sounds like microphonic effect, also only in the right channel, akin to a metallic ringing sound.

Do I have a faulty 6080 or can there be another issue? Many thanks for any advice

[Doc B.]

Sounds like the 6080, but the only way to be sure is to swap in a known good one.

[tsh]

Would you provide a replacement in such case? I don't really have any other tubes at hand as this is my first build. I'm happy to run any other tests to confirm that it's 6080 that is really an issue

[Paul Birkeland]

Grab a wooden chopstick and poke at the connections around the octal socket with an inexpensive set of headphones on your head and plugged into the running amp.

If you poke a solder joint and hear the noise change, then you've found the issue. 

[tsh]

I've just tried poking around with a chopstick, in particular on the joints of the octal socket - I cannot change the noise in this way. But I can definitely easily trigger it (or reduce it) by tapping on 6080 with a finger

[tsh]

Any other ideas please? Or shall I ask for a replacement tube?

[Paul Birkeland]

How is the condition of the pins on the 6080?  Sometimes they can get a little oxidized over the years as they hang out and wait to be used, and cleaning the pins or pulling the tube and reinserting it into the socket a few times can clear up these issues.

[tsh]

The pins look nice and shiny, I've already cleaned them and tried pulling out/reinserting the tube several times earlier, as per advice on this forum. I have done it once again now - it does not make any difference, the noise still appears a few minutes after I switch on the Crack. It's really embarrassing as I have to tap on the tube every now and then to stop it, and then it reappears again after a while.

[Deluk]

The 6080 that came with my kit is totally silent but yours may have some microphonics. I have a couple of 6AS7's, an RCA and a Sylvania, and both of these have a buzz and ring to them which is easy to induce with a tap on the top board or even when I'm typing. My crack is next to my keyboard. But normally it's only apparent when no music is playing and it's not affected by the volume control. Both tubes are slightly noisier on the right channel. Noise is what I'd call only just noticeable, the sort of level you strain to hear when you have an audio test on your ears, so as it doesn't stop me enjoying my HD600's, I'm not too worried.

[tsh]

The noise is clearly stronger in my case - it does not change with volume, but is loud enough to be heard during low- to mid-level passages and to be distracting, it also kills microdetails when it's present. Worst of all, it starts without any apparent reason, even when listening late at night with no apparent vibrations around the Crack...

[Paul Birkeland]

Try poking the power supply caps with the chopstick as well.

[tsh]

I've tried poking all soldered joints and caps already, it has no effect on the noise

[tsh]

I've finally got hold of a cheap Russian tube to try as a replacement for 6080 - and the noise is gone, my Crack is dead silent. Which I believe re-confirms that the original 6080 was faulty - so how do I request a replacement now?

[Paul Birkeland]

You can contact replacementparts(at)bottlehead(dot)com and paste a link to this thread. Please do provide your name shipping address, and order number.  I'd also plan on packing up that tube for return to us.

-PB