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Zenith T724 Selenium rectifier
OldRestorer
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#1

01-26-2017, 12:54 PM
I am finishing up a Zenith T724 and only need to replace the selenium rectifier.

The schematic is in Beitmens pages 182 and 183. each page is marked at the bottom.

http://www.americanradiohistory.com/Arch...n-1956.pdf

I cant see the info on the schematic but I was thinking that since there is a 22 ohm resistor between the selenium and the negative side of the ecaps that a simple diode would work?

  If I remember correctly, The anode goes to the negative side of the wires on the selenium and the diode goes to the 22 ohm resistor and on to the negative of the ecap.

Am I wrong here? Do I need a second resistor or a larger value?

Thanks for any help...

(at least it isn't a resisence line cord) Icon_lol

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Eliot Ness
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#2

01-26-2017, 01:33 PM
Yes, the anode goes to the (-) side and the cathode (end with the stripe) goes to the + side. 

You will probably need to increase the size of the dropping resistor.  You can measure the B+ voltage and substitute higher values of resistance until it reads what it should (probably between 100 - 200 ohms).  To be safe I'd use a 2 - 5 watt resistor.
John KK4ZLF
Lexington, KY
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#3

01-26-2017, 05:06 PM
Thank you!
Just to be clear:::
The wire connected to the Negative of the Selenium goes to the anode. Then Diode end goes to a 100 ohm or so 2 watt resistor. (Remove the 22ohm resistor and replace with the 2 watt 100 ohm?) Connect one end of the new resistor to the diode and connect the other end of the new resistor to the negative of the electrolytics?

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Eliot Ness
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City: Lexington, KY
#4

01-26-2017, 08:32 PM
Yes, you have it correct.  Just guessing on the wattage of the resistor....you might want to use a 5 watter to be safe if you have one.

If you need any diodes I can send a few 1N4007's in the mail tomorrow.  Good luck!
John KK4ZLF
Lexington, KY
"illegitimis non carborundum"
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OldRestorer
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Posts: 4,106
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Joined: Nov 2013
City: Kings Park NY
#5

01-26-2017, 09:01 PM
All figured out...
I could not figure it out... it works when I hook up the selenium but I disconnect it and hook up the resistor and diode and it was dead... I FINALLY figured out that it was a 47K resistor at 5 watts... Not a 47 ohm 5 watt... UGH, Icon_lol

Thank you for the offer but I have many diodes.. And now I have lots of 47K 5 watt resistors... Icon_rolleyes

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Last year: 6
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