[Turnandcough]

I just discovered that a 1950's NOS Mullard I bought four months ago is making a faint crackling sound which increases when I touch it.
The tube seems reasonably well seated in the socket and none of my other tubes are doing this.
It's as if it were more sensitive to vibrations than the others. The DAC it's in is on a heavy shelf with rubber damping pads under it.
Any clues?

[ltr317]

Sometimes vintage tubes, even current production ones, will develop oxidation when they sit unused for a long time, which causes a crackling or sizzling sound.  If you use some very fine sandpaper or emery cloth and clean the pins gently that usually gets rid of the oxidation, and hence the noise.  Other times, vintage tubes may develop micro-phonics or noise from age and there's nothing you can do about it.  So try cleaning the pins to see if the crackling sound go away.   

[Tyson]

Tube's bad, trash it.

[Listens2tubes]

Have you switched tubes and found the source of the noise is this tube? If only one tube is used: Clean the pins and socket. Older socket can loose their grip and may need some "adjusting".

[rollo]

Have you switched tubes and found the source of the noise is this tube? If only one tube is used: Clean the pins and socket. Older socket can loose their grip and may need some "adjusting".

  agree 100%, had similar issues with several tubes and found it was the socket. sometimes the input sleeve loosens or requires a good cleaning. If it persists after the tube may be the culprit.


charles

[Pez]

Possibly the socket. It's happened to me before.

[Turnandcough]

I only noticed this problem with the Mullard.
On the MiniMax DAC the tube is held in place horizontally with spring loaded sleeve. At first I thought the fact that I wasn't using the sleeve may cause the tube to resonate so I began using it again and didn't pay too much attention to it. Then the other day I swapped out another tube and put the Mullard back in with sleeve and noticed the crackling again. I have been busy and haven't had much time to experiment but will try another tube later this evening. Maybe the pins on the Mullard are smaller and fit less tightly but then again the sleeve should solve that.
I wouldn't make a big deal about it except that I paid a pretty penny for that tube and would hate to have to pitch it.

[Pez]

IME mullards do have smaller pins. If you're feeling brave you can try to bend the pins everso slightly to help increase their contact with the socket, but more than likely you either have a bad tube or a bad socket. 

[FullRangeMan]

Sometimes vintage tubes, even current production ones, will develop oxidation when they sit unused for a long time, which causes a crackling or sizzling sound.  If you use some very fine sandpaper or emery cloth and clean the pins gently that usually gets rid of the oxidation, and hence the noise.  Other times, vintage tubes may develop micro-phonics or noise from age and there's nothing you can do about it.  So try cleaning the pins to see if the crackling sound go away.

Most Russian tubes are stored in Siberia, a very cold and humid place, so 6C33 Ulianov pins has a paraffin skin and 6C33 Svetlana has a grey paint to prevent pins oxidation.

[Turnandcough]

Thanks for your advice.
I just tried cleaning the pins with some ceramic stove top cleaner and then with some "cheapo" contact cleaner. The pins remained blackish but I listened for about 15 mins and so far so good.
I think I'll pick up some emery cloth and a can of Deoxit Gold just for good measure. 

[ltr317]

Thanks for your advice.
I just tried cleaning the pins with some ceramic stove top cleaner and then with some "cheapo" contact cleaner. The pins remained blackish but I listened for about 15 mins and so far so good.
I think I'll pick up some emery cloth and a can of Deoxit Gold just for good measure.

I hope you wipe off completely the ceramic stove top cleaner!  That's nasty stuff. 

[2wo]

Get one of those green Scotchbrite pads, much easier and better than sandpaper or steel wool...John