I'm replacing the C37A,C37B Electrolytic 80mfd 40 mfd
But on the schematic drawing It reads C37B, C37D
So which one is the 80mfd?
Also i only have a 100mfd, can i use it for the 80?

I try to send the schematic with this message but i don't know how to?

Hi

I found a 218 with those designations:

http://www.nostalgiaair.org/PagesByMode ... 007621.pdf

This one uses a selenium rectifier with resistor before the 1st filter cap. Since they take plate power for the output tube off 1st filter cap this section should be a high value, 80 mf. Are you replacing the selenium rectifier with a 1N4007 silicon diode? This diode can easily handle surge current of a higher filter cap value.

http://www.diodes.com/datasheets/ds28002.pdf

yes i will be replacing the selenium rectifier with resistor.
I have a 100ohm 5w resistor to use.
Will the 100mf be to big?

Thanks for the reply.

A 100 mf first filter cap will be ok but be sure to add a 1N4007 or similar diode. Not just another resistor.

Hi Norm... just browsing through and saw your comment about the selenium rectifier. Do think it best to always replace those? I have a radio on my "unknown problem" shelf that I haven't been able to diagnose yet, but the rectifier seems to be working ok.... Is it fooling me?
John

John

You will get differences of opinion about replacing selenium rectifiers. Over time voltage drop increases so output will be less. You don't want to be around a selenium rectifier that gets shorted. It gives off a smell like rotten eggs, worse.

Most Zenith T/O's that I've come across have low B+ voltage due to aging selenium rectifiers. A silicon diode like 1N4007 only costs a few cents and will last for decades.

If your shelf radio is a battery/AC/DC type a selenium rectifier with high voltage drop may be the problem?

I don't want to start the selenium rectifier debate again. It's up to an individual if they replace a selenium rectifier. Some are still in use and operating over 60 years.

Yes, it is an AC/Battery model..... I'll check that B+ voltage again.... Good tip, thanks..... And I'm going to stock up on those 1N4007's. You say they can handle house current with no problem, right?

John

John

1N4007 is rated 1000 volts @ 1 amp but they can withstand 1 cycle of 30 amps. Won't have that in radios.