by SDS-PAGE » Tue Jun 19, 2007 9:26 am
I just finished wiring my ST-70 modded with Shannon's board. It seems to bias OK with initial adjustment w/ wire-wound pots at -42.5 VDC max. But when I checked votages across all the tube sockets I am getting around 520 VDC! I checked AC volt feeding 5AR4 at pin 6 and 4, and it's 390 VAC. With the tube in place, I get 530 VDC at pin 8 and 2. Then I checked Volt drop cross resistors on cap lugs and I get 530VDC on D, 530VDC on C and 520VDC on B and 520VDC on A. I don't understand why those resistors aren't dropping more. I am using a mixture of new and original parts for the mod and those resistors are original. Also, 390 VAC on the secondary? Isn't it supposed to be around 360 VAC? I checked the rectifier tube on a tube tester and it's "almost ?/replace". I do have a bad tube? What volt should I get on pin 2 and 8 on a good tube? Thanks in advance.