two new nylon/plastic inserts for my preamp tube cover/lid on my .50 Cal+? Should be the same for the .22 Cal and a few other amps.... I'll try and get a pic up if you have no idea what I'm talking about.
I don't use one in my .50Cal+ heads. I don't use the reverb and my local Mesa boogie repair man told me a long time ago that it would add more gain without it and would not hurt the amp. He was right and I've never looked back.