Quote:
Originally Posted by Tom9589
Why didn't Mike Doyle replace the third 5U4 with a solid state replacement?
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Mike’s comments:
Hi Marshall. Recently I have noticed that the power supply voltages are not stable at the voltages that they need to be at. There are basically 3 voltages supplied here. The Westinghouse prints call them to be 410 VDC and 310 VDC, and 120 VDC. The issue with the variations in voltage are simply design related. The 310 VDC supply is also supporting the High Voltage regulator circuits and the bias on that stage is critical. I was having problems with the High Voltage regulator becoming unstable and causing fluctuations in the high voltage setting. I decided to replace the two 5U4 rectifier tubes that supply the 310 VDC with silicon rectifiers. I added a 300 ohm 50 watt resistor in the system to keep the voltage at 310 VDC since the silicon rectifiers are more efficient than the 5U4’s. I also decided to keep the 5U4 that supplies the 410 VDC since that is mainly for the sweep circuits, and that is all working fine.
Cheers, Mike”