Roland. a gas tube arc will not affect the low voltage PS so one of the relays must have failed but since they are in series both would fsil if one went open coil. I suppose the failure was acutasl contacts allowing the resistor to pass current (not shorted). Your customer seems to have some problem with something causing all these different amps to fail. If it is his 240 line voltage he needs to monitor it or have the POCO check it out.
The Harbach and Ameritron step starts have a long history of failure that has nothing to do with the AC line or tube arcs. The Ameritron is a poor design and the Harbach has underated parts that eventually fail.
While the Harbach uses 1N5408's for the B+ they use undersized 1N4005's as the operating bias. I always replace with just enough 1N5408's to get sufficient idle current. That board also likes to blow HV metering resistors and I replace those with 3 real HV 5M Ohmites.
Having a line recorder on your customers circuit would be a good idea before plugging anything in again.
I will high-pot test your tubes gratis but I will not donate a high-pot. . . I have been testing/autopsying 3-500s and 3-400s for >30-years and I have yet to find a gassy one with an arc mark on rhe grid. . . . If a 110vdc coil dpdt relay is not available for step-start duty in a SB-220, a 12vdc coil relay will do the job if a FWD rectifier-filter is powered by the 5v-rms winding on T1 to produce 12vdc. - note - A series R of roughly 1/3 of the coil Ωs needs to be put in series with the relay's coil to control pull-in.
Originally Posted by AH6RR