Hey guys, I recently acquired a used TSL 100 head and so far I've been really enjoying it. Now that the new is wearing off and I'm working on dialing in tones I have found that on the clean channel when playing I sometimes get a very light crackle. It seems to be more present when playing a high output pickup and also an overdrive set to clean boost. I have ruled out the pedals, the instrument cables, and the speaker cable. The same crackle can be heard when turning the gain knob for the clean channel. If the crackle is present on the Crunch or Lead channels then it's hidden under the distortion but I really tried to hear it and cannot. I've tried replacing the V1 and V2 tubes with spares as well. The amp has Mullard power valves replaced by the previous owner. I checked the bias which was set hot with 85 mV on one bank and 90 mV on the other bank. I rebiased that side to 85 mV as well which is still hot but not at the limit which I understand to be 90 mV. I did some research and a common answer seems to be replacing the main board. That's obviously drastic so I though it couldn't hurt to ask for other ideas before it comes to that as they are $225. Other than that small issue the amp seems to be working well. I've never owned or heard one so I can't be certain. I do need to use the deep switch and run the bass knobs around 6-7 to get much low end but it sounds good that way. This gives it more low than my DSL401 had but I would say not quite as much as my roommates 60watt Peavey 6505+ into the same 4x12 configuration I run (vintage 30s and g12t-75 in an X pattern in high quality birch angled cabs). Thanks in advance for any tips I might be able to use. I'm also open for any other suggestions regarding the amp or settings from those who are more familiar with the amp.