Hiss in left channel - Crack with speedball

[jonnoh]

Hi All. I have a crack OTL with speedball upgrade which is almost two years old now. It has always worked fine until the last few weeks when I noticed increasing noise in the left channel. By noise I mean hiss, or white noise. It's quite noticeable; initially the amp was very quiet. Is this likely to be the tubes growing old, or perhaps some other problem? I do not know much about how tubes work. If a replacement is needed what type is suitable? I guess I'm used to solid state where you can't often just swap one type for another and expect it to work Thanks.

[Paul Birkeland]

Hello Jonnoh,

Is the noise persistent with the volume control all the way up and all the way down?

You could try swapping in a different set of tubes if you like (12AU7 and 6080).  It may also be enough to pop each one out and reinsert it back in the socket, just to ensure good contact. 

It would also be good to look over the voltages to see if anything is drifting, as these may indicate a tube that is being fussy.

-PB

[jonnoh]

Hi, thanks for that. It varies with volume so I guess the problem somewhere around the input side.. I have ordered a few 12AU7s and will of course see if changing this fixes it.

[Doc B.]

If it varies with volume it is from your source, since the volume control is ahead of the tubes in the signal path and thus cannot alter their noise level.

[jonnoh]

Hi Doc, thanks for your advice. I now need to apologise for misleading you as I have had a closer listen just now and the noise seems to be present whatever the volume..it is rather faint but noticeable. I had thought it changed with volume adjustment but it seems that was only in my imagination.