Ok some back ground I built a 5f4 Super Clone out of a Hammond Tone Cabinet Amp chassis. Got it built, but had some issues I could not figure out and gave it to my tech friend to help get out the bugs. He got the amp up and running after fixing some issues one major one was the negative voltage for the bias since the Power tranny did not have a negative voltage tap for the bias circuit so I made up a circuit I found on the net but it still was not right so he fixed that with an other circuit he designed. Some tubes were iffy even after being checked so they were replaced and now it all sounds good except for the following: If the treble pot is cranked all the way it seems like at the last bit squeals when I play the guitar its ok but as soon as I hit a string it gives me like a high pitched feedback sound. Say if the knob goes to ten we are talking in the 8.75 to Ten range. Other wise its fine. Other pots are fine just the treble one. Tech said I should maybe try a 12ay7 instead of the 12ax7 I have in the first position now he wondering if that 12ax7 could be overdriving the circuit to give me that sound? Do you guys agree or is that squeal coming from some other issue? Tech said he would look for a 12ay7 in his stash of tubes this weekend and grab a couple for me to try. I asked about the negative feed back circuit and he assured me they checked that to make sure it was wired right coming off the OT to the 6l6s. I know they had it on a scope and if the feed back was positive that would show anyhow right? Just thought you guys could maybe give some insight on that squeal or high pitched feed back sound. I am hopeing the tube change will take care of it and the 12ax7 is over driving the circut in that VI position.