Reminds me of the mfj "3KW" 986 I once owned. The stub shafts fell out of the
melted form and lots of smoke
was let out. Power output was less than 1kw on 20 meters.
Three turns of the coil [where the roller was positioned] were melted into the
delrin. What a sorry sight.
. Jim -- Delrin® was used for the roller-coil form in an MFJ "3kW"
antenna tuner. During testing at c. the 1kW level in the ARRL lab, the
roller coil form reportedly melted and ignited. The problem is that
Delrin® has a worrisome D-factor at 1MHz, and the problem worsens as f
increases. ABS, or any of the other styrenes, has a lower D-factor. (I
found this info out at a local plastics dealer). Sure, ABS isn't as
nice to machine as Delrin®..
Amps mailing list