Hi I was poking around the forums and I see your name come up a lot as someone who can do repair work. I have an older JL Audio 450/4 that has something wrong with one of the channels and was wondering if you'd be interested in doing some work on it. Thanks!
These amps don't use mica or kapton insulators. Just the strips that are sandwiched in between the sink and transistors. If you nicked the strips it might/will short the casing of the transistor. Always check for shorts by ohm-ing the transistors case to the chassis with your dmm, if you read 0 ohms you know you got a short between the sink and transistor.
As for the two transistors that don't have the pressure bar, those use a screw to push them against the sink. The screw holes should be there already. These are the plastic casing and don't require insulators (double check them to make sure they don't have metal behind them.
I had a question about a PG XS4300 that I was wondering if you could answer. It's probably really easy too. I bought the amp off of ebay a few years back for cheap just to find out that it didn't work. I took it apart and found 3 mosfets blown and no thermal pad/tape between the chassis and the fets.
I put in thermal pads, went to mount the board: 14 of the mosfets are paired together and sandwiched between an 1/8" piece of aluminum and the chassis. I have two mosfets at the end on each side by the RCAs and two more screws, but no more aluminum pieces. I'm trying to find out if there may have been small pieces securing these fets to the chassis or if they mount directly to the chassis w/o being sandwiched. Do you know?