07-30-2016, 12:38 AM
I've restored about a dozen or so Heathkit/Eico/Knight signal generators. Got at least eight more awaiting their turn. Each one is a lot of fun to do and the transformation always satisfying.
Now I do the dropping resistor just a little differently. I add it in the secondary, just between the transformer and the 1N4007 diode which replaced the selenium rectifier. It limits the inrush current to the first filter capacitor, (usually a 20/22 ufd). A half watt resistor is all thats needed. I determine the value of the added resistor by clipping a 10K pot where the new resistor will be. Then adjust the pot to dial in the proper voltage for the B+. It runs between 200 ohms and 1K. All depends on how much voltage drop was across the old selenium diode and what the present voltage you've got coming out of the wall.
I'm wondering if your approach is better or worse than mine? Does the resistor run warm? Mine doesn't. I'll have to post a photo of a similar signal generator that's in the restoration queue, so you can see how my approach looks. I'd bet you could make valid arguments for doing it either way. Something to ponder.
Mitch
Now I do the dropping resistor just a little differently. I add it in the secondary, just between the transformer and the 1N4007 diode which replaced the selenium rectifier. It limits the inrush current to the first filter capacitor, (usually a 20/22 ufd). A half watt resistor is all thats needed. I determine the value of the added resistor by clipping a 10K pot where the new resistor will be. Then adjust the pot to dial in the proper voltage for the B+. It runs between 200 ohms and 1K. All depends on how much voltage drop was across the old selenium diode and what the present voltage you've got coming out of the wall.
I'm wondering if your approach is better or worse than mine? Does the resistor run warm? Mine doesn't. I'll have to post a photo of a similar signal generator that's in the restoration queue, so you can see how my approach looks. I'd bet you could make valid arguments for doing it either way. Something to ponder.
Mitch
