Find some Orings at the hardware store to fit the shaft of the cage, to allow the necessary clearance. You probably need 2-3 for the required lift.
If you do a search, there are other ways owners done it. I use the old RCA 6L6G big bottle in my PL HP, which just fits under the cage.
If you do a search, there are other ways owners done it. I use the old RCA 6L6G big bottle in my PL HP, which just fits under the cage.