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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.
[–] • 1 pt

This looks infinitely more fun than what I'll be doing today. My son seems interested in electronics, but I'm big dumb in that category. Any suggestions for a beginner project to start learning the fundamentals?

[–] • 1 pt

So...one other thing I found is this:

https://www.robotshop.com/products/130-in-1-electronics-playground?

That's a lot closer to what I had. In fact, I wonder if elenco made those old spring kits for ratshack...

[–] • 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.

[–] • 0 pt (edited )

That's actually kind of a tough one, the stuff I grew up on (Radio Shack x-in-1 kits don't exist anymore, and most of what you get from "electronics exploration kits" these days is arduino junk...that's not electronics, that's programming.

If you want something that looks easy to use and is equivalent to those kits from years ago, this is probably the closest thing:

https://www.amazon.com/Snap-Circuits-SC-300-Electronics-Exploration/dp/B0000683A4?th=1

It's a multi-part kit that explores pure electronics. This is not a recommendation from me for this particular kit, just that it looks like what I had - except updated. That would be a good place to start, then you can move on to buying breadboards and loose components. Elenco has been around for a long time, they've made odds n ends over the years so it's not like that's a new company.

Perhaps @Morbo or @webrustler would have some input as well.

[–] • 1 pt

Oh nice, I was imagining that soldering / crimping would be a necessity. I appreciate the input. We'll definitely be checking that out.

[–] • 1 pt

Soldering comes later...kits like this allow you to build without actually ruining parts.

You're welcome and I'll see if I can find anything else...if nothing else, old radio shack stuff is still common enough on ebay that you could pick one up.