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I have this meter on the bench that had some repairs recently, one of the items on the list for it included replacing the old selenium rectifier.

These parts were a stopgap device between vacuum electronics, and modern silicon electronics. Made from Selenium Oxide, they acted like a diode with a massive voltage drop. You can't just place a modern diode where they are, you need to account for the extra voltage drop. This is done with dropping resistors in series with the new diode.

This one has a multi-voltage supply, so the situation is a little more complex, as I have to account for both voltages with appropriate dropping resistors. Technically, as I'm simulating the drop here, the second voltage should line up but it doesn't - it's about 9V low.

I had taken some current measurements, but the selenium device popped before I could finish, so I'm left making assumptions about current flows and resistance.

In the picture, the meter itself is under test, I have the new diode and dropping resistor (adjustable) on the bench where I can make changes. So far, with modern line voltage, I am able to get 130VDC B+ (#1) with 1.27k. I don't need 7 watts worth here, that's simply what I had - I'll probably use two 1W resistors in each leg when done.

I have this meter on the bench that had some repairs recently, one of the items on the list for it included replacing the old selenium rectifier. These parts were a stopgap device between vacuum electronics, and modern silicon electronics. Made from Selenium Oxide, they acted like a diode with a massive voltage drop. You can't just place a modern diode where they are, you need to account for the extra voltage drop. This is done with dropping resistors in series with the new diode. This one has a multi-voltage supply, so the situation is a little more complex, as I have to account for both voltages with appropriate dropping resistors. Technically, as I'm simulating the drop here, the second voltage should line up but it doesn't - it's about 9V low. I had taken some current measurements, but the selenium device popped before I could finish, so I'm left making assumptions about current flows and resistance. In the picture, the meter itself is under test, I have the new diode and dropping resistor (adjustable) on the bench where I can make changes. So far, with modern line voltage, I am able to get 130VDC B+ (#1) with 1.27k. I don't need 7 watts worth here, that's simply what I had - I'll probably use two 1W resistors in each leg when done.
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[–] • 1 pt

Nice. It might be a bit frivolous to judge a book by it's cover but I like the aesthetics of that one.