for those not wanting to wind their own filament winding ......,
the latest sales flyer from mcm (800 543 4330 or
www.mcmelectronics.com) lists an isolated crt brightener prt # 33-595
this is a transformer that will connect to the original filament winding (primary) then to the crt filaments ( secondary)
thus isolating the cathodes from the heater's ground loop . the secondary voltage will be higher providing the brightener effect . just add series resistance at proper wattage if no brightener needed....
haven't seen these available for a number of yrs ! and still cheaper to wind yer own

qrz