Crack "crackling" question

[Baobei]

Hi,

I installed the Speedball last week and have been listening for a couple of hours. It sounds very very good!

However, suddenly I started to hear a "crackling" noise in the left channel. I can't reproduce the sound which seems to appear randomly, but I can hear a high pitched "rattling" sound when tapping on the top of the crack (doesn't change when turning the volume pot). So I rechecked all the solder joints, with special attention to the left channel. All seems good.

However, I noticed that my 6080 makes a rattling sound when shaken slightly and the sound I can hear through the headphones when tapping on the Crack sounds very similar. After re-inserting the tubes etc. the 6080 started doing some crazy arching at switch-on, that died down within about a second though.

Do I have a broken tube? (Tung-Sol 6080 that came with the kit)

Thanks,
Simon

PS: Apologies for the slightly weird sound descriptions, English is not my first language...

[Paul Birkeland]

How are your voltages?

[Baobei]

Thanks for the quick response.

Voltages:

1. 76
2. 185
3. 0
4. 185
5. 77

6. 0
7. 110
8. 0
9. between 110 - 111 (meter fluctuates)
10. 0

Small Speedball PCB:
OA: 76
IA: 185
B-A/B: 0
IB: 185
OB: 77

Large Speedball PCB:
OA: 111
OB: 110
G: 0
B+: 185

During V-check the tube didn't flash. After turning the board over (after unplugging and waiting of course) I tried it again as it looks normal as far as I understand. This time the tube flashed again. Music plays normally (left sounds a tiny bit less loud, but that could be my mind playing tricks). When gently tapping the 6080 there was the "crackling" noise again in the left channel.

Resistance check looks normal as well as far as I can tell (OB and OA 700+ohm).

[Paul Birkeland]

Is there any white discoloration of the silver getter inside the glass of the 6080?

How many hours do you have on the tube set?  Sometimes issues like these can resolve themselves with some burn in time.

[Baobei]

There are some small white flakes stuck to the glass inside and the silver seemed to have moved down a bit (see picture). Anything to worry about?

The tubes have maybe 30-35h on them now. I cleaned the contacts with some steel wool and it seems to run normally for now...

Thanks for the great support btw! Quite an adventure those tubes!

[Paul Birkeland]

The tube on the left is what I'm referring to.  A lot of the time arcing in a tube is from gaseous contamination, which will absorb into the getter over time.

[Baobei]

Thanks for the explanation!

Apologies for the late reply. I finally had some time to continue trying things out.

The noise in the left channel started again after ca. 1h listening and I was able to reliably recreate it. Just to check I did the "pocking with chopstick" thing without a result. However, when switching the Crack on when upside down the tube started arching again like crazy.

So, I went ahead and bought a cheap tube on ebay to test. All problems seem to be solved (ca. 3-4h burn-in so far), so I think I must have just gotten a bad tube.