Replacing Selenium Rectifier

[rave0035]

It's been a while since I've done this. What do I need to make sure B+ stays relatively consistent here?


Gracias in advance for the help.
Mike

 

[rave0035]

Whups, that's a little small. Here's the PS:



Mike

 

[gadget73]

Depends on what you get as an output voltage, but I'd probably bump the value of R60 to adjust it. Can't quite read the value, but to guesstimate, another 10-47 ohms in that spot will probably make it right. Measuring the voltage drop across the existing resistor will confirm the current, and a little Ohm's law magic will tell you what value needs to be in that spot.

 

[rave0035]

Check my dummy math, please.

R60 is a 440ohm resistor. It drops about 18v, so...

I = V/R
I = 18/440ohms
I = .04amps

Current output voltage is about 143vdc.
With a diode in place, we see about 155vdc. So...

R = V/I
R = 12/.04
R = 300ohms?

Mike

 

[BinaryMike]

The right place to add series resistance is directly in series with the replacement rectifier, but because capacitor charging current flows in sharp pulses, it's difficult to calculate the necessary resistance value. This is one case where cut & try works best.

 

[rave0035]

Seems that way. I threw a 150ohm 2w resistor in series before the first filter and got it to 140v output. I'm happy with that! If I had a slew of other 2 or 3w resistors I'd try to get it closer but I don't. Good enough.

Thanks to both of you,
Mike

 

[gadget73]

Thats why I'd have bumped the resistor after the cap instead of adding one before. Easier to calculate, just need to make sure the cap can handle the extra voltage.