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Old rectifiers - Printable Version

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Old rectifiers - TV MAN - 06-20-2015

I just picked up a 50's model Philco tv, not sure of the year or model yet. It was a barn find. Shame. But, I did save it from the dumpster! It had been out there just long enough to damage the bottom of the cabinet, grill cloth and put a little very light surface rust on some things. Set is complete, and had been purchased new by this family. I guess it was put out shortly before the owner died. I took a look inside so see how much rust or rodent damage was present (thought of it for parts at 1st) but things didn't look too bad. I may take a shot at a rebuild a little later. It is a split chassis, but looks much simpler than another Philco I have. This one has the 2 large selenium rectifiers instead of the 5U4. I wondered what it takes to replace those. Thought of a couple 2.5a diodes stacked (paralleled). Anyone done this?

Anyone restored a blonde cabinet before? Other then some loose veneer at the bottom and some inside structure/supports needing replaced, the cabinet is intact. I don't know if this type of finish can be duplicated. This could be very neat old tv. I'll try to post some pics down the road when I get my 'shop' ready - still a work in progress...

RE: Old rectifiers - Radioroslyn - 06-20-2015

I've used a couple of 1N5408's in a few tv's I've serviced. Worked fine.
GL
Terry

RE: Old rectifiers - David - 06-21-2015

IN5408 3AMP/1000PIV cost around 35 cents each, IN5406 #AMP/600PIV cost around 25 cents each. When I installed diodes I will do series just in case one fails. So if you do series and paralled cost is no more than a couple of bucks. Look forward to seeing the finished project. David

RE: Old rectifiers - Arran - 06-24-2015

(06-21-2015, 07:07 PM)David Wrote:  IN5408 3AMP/1000PIV cost around 35 cents each, IN5406 #AMP/600PIV cost around 25 cents each. When I installed diodes I will do series just in case one fails. So if you do series and paralled cost is no more than a couple of bucks. Look forward to seeing the finished project. David

 They are even cheaper then that if you buy some off of Mouser, I think that they were around $.15 each through there, so even less of an excuse not to double up on them. The reason I investigated was for the diode dropper trick in early AC/DC radios and series string TVs, much cheaper to buy an extra diode then a new set of tubes if one shorts out.
Regards
Arran

RE: Old rectifiers - codefox1 - 06-24-2015

Agree, diodes will be fine, mind you ALL the electrolytics and, yes, all the paper caps must be replaced before you dare turn it on. Might want to find out if the CRT is good first.

You'll get more on blond cabinet refurbishing by making another post in cabinets forum. Been a whle but I recall stripping, staining a darker color on a couple of 50's TV Cabinets.

RE: Old rectifiers - TV MAN - 07-02-2015

Thanks for the replies! I am curious about the diode dropper trick. Any info on that would be appreciated. I had never thought of putting diodes in series like that. I could see that saving problems if one shorts. Do these need any kind of dropping resistor added?

RE: Old rectifiers - David - 07-03-2015

Good Morning you will need some kind of dropping resistor. Old selenium rectifiers drop around 7-10 volts in a radio silicon diodes drop 7/10 of a volt in a radio!!! Desired voltage drop divided by amps equals ohms, go with your best guess then measure results and adjust. Good Luck David

RE: Old rectifiers - wa2ise - 07-04-2015

There's a complication in calculating the resistance you'd need. The diode will only be passing current at the peaks of the 60Hz waveform. That's when the filter cap is "topped off" (I'm not talking about initial power up). These spikes of current are about ten times the B+ supply current the tubes are pulling. Again it's a best guess, and adjust accordingly.

RE: Old rectifiers - Joe Rossi - 08-16-2015

Hi Tim, check out the link:

www.w3hwj.com/index_files/RBSelenium2.pdf

Replacing Selenium Rectifiers Further Thoughts Six Years Later Since the Antique Wireless Association published my article in January of 2007.


Rich Bonkowski does a great job explaining.  Joe