Gosh, I hope I did this right!
 

Back to work on the '53 Philco, I finally tackled the selenium rectifier replacement and even if I screwed it up it was fun and it sure looks purty.

I really am not totally sure if I used exactly the correct diode/resistor combination, but I *think* I'm in the ballpark anyway, based on quite a bit of reading up on it first. I used an IN4007 1A, 1000 volt diode and a 2 watt, 47 ohm resistor for each of the two rectifier replacement assemblies, and I wired them in properly as far as I can tell. It's hard to believe that these little doo-hickeys can adequately replace those big blue spaceship looking thingies.

Probably this weekend I'm gonna toss it loosely together and try a low voltage power up to see if I get any signs of life. If I do then I'll start on the capacitors!


Raddion


--- I have the whole Honeymooners series, also Captain Video and Clutch Cargo haha... but it's LOST IN SPACE I'm most looking forward to watching!!!

Yes, those diodes will replace those bulky selenium rectifiers, but be careful of diode polarity. Some selenium rectifiers have a + mark which actually goes to the electrolytic capacitors, which is the cathode side of the diode marked with the strip on the diodes. Bring it up slowly, measuring the voltages at the electrolytic filter capacitors making sure the polarity is right. If you have a variac, even just apply 10 volts or less to start and check the voltages on the capacitors. You don't need to blow the electrolytic capacitors or the power transformer. Very nice wiring job.

I was just going to say the same as Walter did. using a variac to confirm B+ in the right directions.

I one time goofed a top hat style silcon diode. I just grabbed one and put it in the same way as the one that came out. it was in a voltage doubler circuit, and turned out it was revesred from the orig diode. Up till then I did not realize that top hats came in two styles (reverse polarity). the variac saved me as I was getting some really strange readings the way it was done.

The cathode end of the selenium stack is marked "+", meaning "da B plus comes outa here."
The banded end of the Si diode is always the cathode.
The old top hats can fool you.

Thanks a lot guys for the cautionary tips - I definitely don't want to blow this thing up. I'm a master auto tech with only a basic understanding of this type of stuff, but I have learned to proceed with caution over the years! I leaned heavily on this article for the selenium replacement:

http://w3hwj.com/index_files/RBSelenium2.pdf

If you scroll down to the top of the page marked 28 there is an image of a diode setup that I tried to duplicate as closely as possible. To the right of that, under the heading "Replacement Considerations" are the instructions on wiring that I followed, wiring them in series into the chassis. I am hopeful that I didn't goof somewhere, I have re-read it a hundred times!

So, if I want to check for DC voltage when I power it up, I can kind of figure out where to probe with my positive lead, but where do I pick up ground? Being direct current, is it probed at the chassis?

As long as you got the polarity right you should be fine.

To expand on coot's comment, the band on silicon diodes also means "the B+ comes out of here."

To answer your question, yes, the chassis should be ground for the B+.