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Old 08-09-2002, 08:20 AM
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CTC-4 Voltage Problem

All caps have been replaced and I've bypassed the selenium rectifiers w/a pair of silicon diodes. I've got 23K+ high voltage--at the lowest setting--and the plate in the horiz output tube is going red at 110V line voltage. Hmmmm. Could the higher efficiency of the new diodes be the cause here? I'm getting 350+V at pin 1 of the HO tube where the schematic says it should be about 150V. The 10W 11,000 ohm resistor and 56 ohm resistor just ahead of the tube both test OK. That, plus the HV being at the recommended voltage at the lowest setting makes me think I've got too much B+ going in somewhere. Think I need to put a 10W resistor in series just after the rectifiers? Your suggestions welcome!
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Old 08-09-2002, 09:32 PM
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CTC-4 problem

I got the voltage down now but the plate's still going red. Other voltages are pretty much ballpark--(-58 and -20V). This is just bench testing the chassis at this stage and the CRT is not in the circuit yet. Also, I note that I replaced the 3V, 1000mfd cap with a polarized electrolytic; the schematic calls for a non-polarized unit. Suggestions? Was there a way to connect two polarized electrolytics to get a non-polarized configuration? Seems as if I read something on this somewhere but can't remember where. Checking the AES catalog, I can't seem to find anything but polarized.

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Old 09-20-2002, 06:37 PM
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jshorva65 jshorva65 is offline
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To replace a 1,000uF/3V non-polarized electrolytic capacitor, connect two polarized 2,200uF/6.3V units in series "- to -" like this ... + ---|(----)|--- + The net capacitance will be 1,100uF/6.3V non-polarized. Connecting two identical capacitors in series halves the capacitance and doubles the working voltage, but connecting them back-to-back halves the capacitance and changes the voltage rating to non-polarized.
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