some build notes:
· The 360R KSA1156 emitter resistors set the current to the 3rd stage. The original BH ran 10mA, the 360R resistors in current version set it to be about 3mA to reduce heat. If you decide to raise the current, make sure you compensate for it by lower initial value in offset adjustment.
· The boards are designed T2 style – the tubes are mounted on the back side of the board. I also mounted the LED, all trim pots and the 50R CCS resistors on the back side for ease of diagnosis and adjustment.
· Be VERY CAREFUL when you measure the voltage across the 50R CCA resistor next to the 24V zener. There is significant voltage potential difference between the two and they can get arcy sparky easily – it happened to me twice when I was testing/adjusting the CCS current - big bang, magic smoke and flying silicon pieces. I ended up mounting those 50R resistors tall to give additional Clarence.
· Also be careful with the DN2540 in the CCS, their exposed tabs are live.
· It should be obvious but the PZTA06 and PZTA56 SMD are to be mounted vertically observing the pinout.