2019-06-11 Selenium Rectifier Burned Up, How To Replace

from FB group Vintage Transistor Radios Jun 12

Bob Kirsch has the right idea, but the single replacement diode *must* be rated for 400 V peak inverse voltage or more. A 1N4007 is cheap and readily available. I assume you’re in a country where the AC line voltage is 120 VAC, because the rectified DC is 135VDC according to the schematic. The tubes/valves do not draw current for 11 seconds when first turned on so the DC across the 80 uF capacitor can be as high as 170 volts, so it’s best to use a capacitor rated for 200V or more.

As he said, increase or add to the 22 ohm resistor to obtain 135VDC when the set is fully warmed up. The resistor(s) wattage rating(s) must be at least the voltage across the resistor squared divided by the resistance. So if the voltage across it is 30 volts, and the resistor(s) total 100 ohms, then 30 times 30 divided by 100 is 900 divided by 100 equals 9 watts. A 10 watt resistor would work but get very hot, it would be better to use a higher wattage or two 10 wat resistors in series. And make sure they don’t overheat other components.

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