Strange Problem, help me understand this

[Ripthorn]

So I am working on my submini tube amp project and etched up a pcb for it and put it all together. I tried it out today and it sounds great. Then I wanted to play it very quietly after the little one was in bed, so I turned the volume knob down and got sound out, but the problem is that I was getting lots of distortion out of what was supposed to be pretty clean. I turned the volume all the way down and still got the same low level distortion sound. The volume knob is pre PI if that helps. I think a somewhat related issue is that my signal ceases to exist at my third gain stage (it was working perfectly a couple hours earlier and I didn't do anything to it).

Anyway, that is a little rundown of the problem, let me know if more info would help. Any suggestions are appreciated.

[Bob-I]

You'll need to locate the source of the distortion before troubleshooting can start. Connect a clean sine wave at the input and look at the output of each stage for distortion. Once you locate the source it should be easy to find the cause.

If you don't have a scope you can listen to the stages but coeencting a clip lead to a fairly large cap, .1/600V, and the other end to a test power amp/speaker. You should be able to hear the distortion, but this is not as good as a scope because you may get impedance mismatch distortion on the input of the test power amp.

Good luck.

[Ripthorn]

Well, I have found that the distortion is actually coming from the preamp. Right now I have the preamp wired with jumpers so that the distortion channel (just an extra two gain stages) is activated. It seems that some signal from there is getting into the PI somehow. The PI is a cathodyne, but there shouldn't be any leakage between triodes inside the tube. I know the simple solution is get rid of the jumpers, which I will do eventually, it just seems that if the PI is not connected to the last preamp stage, then there shouldn't be any signal getting in. Is this a transmission problem?

[Structo]

Got a schematic?

Could it be coupling that is transmitting the signal?