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 Selenium rectifier replacement/voltage question

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dschulma

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PostSubject: Selenium rectifier replacement/voltage question   Sat Oct 16, 2010 2:57 pm

I've replaced the selenium rectifier on my Zenith C845 with the appropriate diode/resistor combo. I measured the voltage after the resistor and come up with 126.4 VDC, which is fine, however, I also see a 5.6 VAC component as well. Is this normal? Unfortunately, I didn't measure any voltages with the selenium in place so I could compare the two. Any explanation or thoughts would be appreciated.

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David, WD0ERU
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TexMac



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PostSubject: Re: Selenium rectifier replacement/voltage question   Sat Oct 16, 2010 3:20 pm

Are you measuring before or after the filters?
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dschulma

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PostSubject: Re: Selenium rectifier replacement/voltage question   Sat Oct 16, 2010 3:34 pm

Ahhh...before the filters, that would explain it! (I think)
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TexMac



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PostSubject: Re: Selenium rectifier replacement/voltage question   Sat Oct 16, 2010 7:54 pm

Likely, but there are some other considerations. A DMM might show some AC riding through, but a 20,000 Ohm/V analog meter may not due to loading. Sometimes you can see some weird stuff with a digital meter. Remember the readings on your schematic were usually with the radio on, the volume control full on and no signal. The readings were also based on typical instrumentation in the typical service shop at the time the radio was built. About the best available might be a VTVM for the grid circuits. If you work on very early sets the voltmeters were even more dicey.
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dschulma

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PostSubject: Re: Selenium rectifier replacement/voltage question   Sat Oct 16, 2010 8:56 pm

Thanks for the info, makes perfectly good sense! I'll have to try it with my RCA WV-98C and see if I get an AC reading.
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tubes4life



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PostSubject: Re: Selenium rectifier replacement/voltage question   Sat Oct 16, 2010 9:22 pm

I wouldn't even bother checking; I'm sure it's fine.
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