[Amps] Heath SB-220 Soft Start

[Larry Carpenter]

Hi Folks,

                Its been a while since I posted anything but I do enjoy reading messages on this group. I find them very helpful. I just recently acquired an SB-220 with all the Harbach mods, soft start, soft key, metering board and power supply board with new caps and bleeders. I used this amp for a couple of days and it worked fine with 3000 VDC in the SSB position with about 1100 watts out and about 2250 VDC in the CW position. While sitting in a idle state there was a flash and it immediately lost power. After some investigation I found one of the wire wound ceramic resistors (20 ohm @ 10 watts) had opened up and left a black zorch on the soft key board.  It also appears that one post of the 48VDC K2 relay got really hot. It looks like these resistors will be easy enough to replace but I am concerned at what caused the resistor to open up. I am wondering If I should replace the resistors and take the tubes out before powering on and see what happens. Neither of the circuit breakers on the back of the amp had tripped. Just wondering if anyone else had run into this problem with Harbach Soft Start module. Any advice greatly appreciated.
                                                                                                                                                                Larry Carpenter
                                                                                                                                                                AA4VI