mikeyB
Well-known member
Can any of the gurus validate (and hopefully resolve) my concerns?
Built 2 DOAC - 1st one I can't get my hands on it as me mate is constantly using it for mastering! Now I've finished the 2nd (Kubi advanced version), I've started to confirm my niggling suspicions re. the power supply caps.
PCB ident is for 400V rating - BOM is for 350V and if like me, any UK builds using 350V may have a problem.
Musikding power transformer has 250V HT secondary. Doing the basic math 250 x 1.414 = 353Volts :sad: This is before taking into account UK mains - mine measures a rock steady 240V :!: Accounting for this increase, DC after rectifier is calculated at 369V :shock:
While valves are warming up - no current is drawn, and I measured 370V after the rectifier. This stayed this high for 15 - 20 seconds until the valves conduct :!:
Is there an easy fix for this (inclusion of a power resistor somewhere) or do I need to take out the PCB and upgrade the caps to 400/450V rating :roll: Will this be the case for all 12 HT caps or just the 3 pre-regulator?
Will do a bit more measuring and observation before reporting back :shock:
Built 2 DOAC - 1st one I can't get my hands on it as me mate is constantly using it for mastering! Now I've finished the 2nd (Kubi advanced version), I've started to confirm my niggling suspicions re. the power supply caps.
PCB ident is for 400V rating - BOM is for 350V and if like me, any UK builds using 350V may have a problem.
Musikding power transformer has 250V HT secondary. Doing the basic math 250 x 1.414 = 353Volts :sad: This is before taking into account UK mains - mine measures a rock steady 240V :!: Accounting for this increase, DC after rectifier is calculated at 369V :shock:
While valves are warming up - no current is drawn, and I measured 370V after the rectifier. This stayed this high for 15 - 20 seconds until the valves conduct :!:
Is there an easy fix for this (inclusion of a power resistor somewhere) or do I need to take out the PCB and upgrade the caps to 400/450V rating :roll: Will this be the case for all 12 HT caps or just the 3 pre-regulator?
Will do a bit more measuring and observation before reporting back :shock: