I'm converting a 1950s Harman-Kardon C-100 mono hi-fi amp for guitar use. This is a total teardown and remake into something 18-wattish. The amp is originally an ultralinear design with 2 6CM6s (small bottle 12 watt 6V6s) in PP, cathode bias. B+ will be around 350-375V. I contemplated ditching the UL taps but I think instead I might try it as UL with little or no NFB and see how that sounds. From the factory this had no screen stopper resistors, but it was also designed to be never overdriven with B+ around 305V (screens idling at 310V). When I look at Fender UL schematics, it looks like they put 470 Ohm 1W resistors on 6L6 screens (500V B+). Any advice? Add screen resistors? If so, what value?