Tinkles, Snaps, Crackles, and a Faint Glow

[karl]

I just finished my Crack, which I bought last May or early June. It sounds very musical.

However, I do have a few questions about its characteristics. Remember that I am new to tube equipment.

- There is a very faint bluish-gray glow in the 6080 when switched on. It can only be seen in a completely dark room. It is momentary and then the filaments light.

- There is hard "snap" in the right channel when I power-down.. I assume that this is DC discharging through the headphones. Is this damaging? Why only the right channel? I am not sure that it happens every time I switch it off.

- Occasionally, there is a loud crackling sound in the channel. This does not occur when I adjust the volume.

- Upon switching it on, I hear a tinkling sound. I am assuming that I am hearing the interior structure of  the tubes expanding due to thermal expansion and microphonics. It is slight and only occurs for a few minutes sporadically.

The kit when together very easily and everything checked out fine during testing.

Any thoughts?

Regards,

Karl

 

[Doc B]

- There is a very faint bluish-gray glow in the 6080 when switched on. It can only be seen in a completely dark room. It is momentary and then the filaments light.

That's pretty typical and not a problem.

- There is hard "snap" in the right channel when I power-down.. I assume that this is DC discharging through the headphones. Is this damaging? Why only the right channel? I am not sure that it happens every time I switch it off.

That might be from a tube, at least the place to start to figure out where it is coming from might be trying different tubes. In the meantime it wouldn't hurt to unplug the headphones before you power down just to be safe.

- Occasionally, there is a loud crackling sound in the channel. This does not occur when I adjust the volume.

Probably either a tube or perhaps a cold solder joint. If tube swapping doesn't resolve it, it might be worthwhile to reflow your solder joints.

- Upon switching it on, I hear a tinkling sound. I am assuming that I am hearing the interior structure of  the tubes expanding due to thermal expansion and microphonics. It is slight and only occurs for a few minutes sporadically.

Yes, this is very common and not a problem.

 

[karl]

Doc -

Thanks for the reply.

Where in particular could the cold solder joint be regarding the crackling sound? If it's a tube, which one is it likely to be?

I forgot to mention that the loud crackling sound is in the right channel only.

Regards,

Karl

 

[hasafraker]

either tube (at least in my experience) could be the cause of microphonics, my first 6080 hummed, swapping it got rid of that, then I noticed that the 12au7 I started with was VERY microphonic and anything from tapping the headphone cable to tapping the stand or the chassis would ring right through to my headphones, swapping that tube out solved that, the set I'm currently running are very quiet.

 

[karl]

Yes, my tubes are very microphonic, especially the 12AU7. I too get the ringing through my 'phones. It may be time to start tube rolling.

Regards,

Karl

 

[spear321]

Had the same poblem In my KIT6550 amp.
The rIght channel cracklIng and consIderIng I had just upgraded the capacItors was very worrIed.
Pulled out the tubes plugged them back In and It stopped back to sIlence.
Can only assume bad contact In tube socket now make sure when I change them to put them In twIce and make sure they are well settled.

 

[ironbut]

It seems like just about anything with current running through it can be microphonic. Cold solder joints, bad tube sockets and wires. If fact, one thing I've learned from troubleshooting gear is to tap on each component and wire to track down problems. When I finish a project and even if there aren't any problems, I take a wooden chopstick, turn up the volume and tap on everything to head off trouble. I almost always find something that needs a bit more solder or just needs to be shifted a little.
So, sometimes when I find a tube position that's microphonic with more than one tube, I start by cleaning the socket contacts, making sure that all the pin receivers are tight and check that solder joints are good and don't have any peaks which might tend to arc to another contact (tube pins aren't all exactly the same size so some might move the pins inside of the chassis more than others).

 

[dstrimbu]

either tube (at least in my experience) could be the cause of microphonics, my first 6080 hummed, swapping it got rid of that, then I noticed that the 12au7 I started with was VERY microphonic and anything from tapping the headphone cable to tapping the stand or the chassis would ring right through to my headphones, swapping that tube out solved that, the set I'm currently running are very quiet.

Agreed - my "stock" 6080 hummed in one channel (right); replaced it with a NOS Sylvania 6AS7G and the noise floor dropped noticeably.

Ironbut is spot on regarding solid connections / joints & sockets; you're dealing with high voltage DC and arc-over is very possible if connections are dodgy in the slightest.  I like his chopstick trick, also. 

Cheers,

-Don