I may have made an error connecting number 36 .04 capacitor (listed on the schematic below) to the rear prong on the volume control.
I connected #36 to the negative prong at the rear of the volume control.
However, the schematic shows a capacitor between the two power cord lines.
Have I mis-soldered this cap onto the wrong prong at the rear of the volume control?
Presently, I am getting a loud hum. All other work has been done. All parts installed double checked.

Thanks in advance.


http://www.nostalgiaair.org/PagesByModel/325/M0013325.pdf

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Pretty simple request, but the picture does not show enough (for me) to answer the question. That capacitor simply connects across the line. One side goes to the on/off switch (on the back of the volume control) and the other side goes to the 120 line. Should be using safety caps in that location. If they fail, they fail open so that you don't get a short and a fire.

Is that the capacitor with the green spaghetti? That wouldn't be right for #36.

Ed

You have the AC switch wire within 1/18th of an inch away from the most hum-sensitive wire in the whole radio, the wiper of the volume control. That's 353 volts peak to peak right by a wire that only needs to pick up one ten-thousandth of that in order to hum like crazy. It's going to happen.

Unsolder the wires going to the line switch, twist them along their length (this helps cancel out hum) , then run the, along the edge of the chassis, as far away as possible from the center volume control wire and parts connected to those wires.

Also for the capacitor across the power line, place it so it also is away from the volume control wires.

For even less hum, use a polarized line cord and run the neutral wire to the power switch.

Thank you for your responses.



Actually, my computer had a .03 cap between the two power line cords rather than the .04 as stated in use on the schematic. So, the two yellow caps in the photo in parallel are a .02 and .01 for the .03.

Yes, apparently, I mis-soldered the .04 (my .03) on the schematic (#36).
Tomorrow I will make the change and resolder the .03 to the powerline cord attached to the back of the volume control.
The radio worked well except I had to remove, take apart, and clean the volume control. When reinstalling the volume control I miswired the schematics #36.

Ancient_Hacker, thanks for the tip about reducing hum.

Oh wow! I see that C36 across the line. My approach would be to replace it with a 1 KV ceramic disc capacitor. If not that, leave it out of the circuit and plug the radio into your computer's backup power (often called UPS or APC) or a surge suppressor.

http://www.mouser.com/Search/Refine.asp ... S9-102J-RC

if it where me I would have used a .05 close to .04 , some radios used a .047 600volt , think zenith did

Tomorrow, I will remove the .03 (the original old paper value cap found in the set) and replace with a .047, 600v.
Also, I have the .047 1000volt available. Would it be better to replace the 600volt cap with a 1000 volt cap??

The power line is subject to all kinds of transients and/or voltage spikes. They can come from pieces of equipment being turned on or off, accidents where poles are knocked down, lightning hits, loads being switched, etc. Therefore I would say that if you're going to include this capacitor across the line, the higher the voltage the better. Maybe you should consider substituting an MOV such as the V250LA40BP.

http://www.mouser.com/Search/Refine.asp ... V250LA40BP
http://en.wikipedia.org/wiki/Varistor

either one will work just fine

Daniel,

Although the DC-rated capacitors mentioned so-far will "work" as across the line filters, it would not be a bad thing to use a modern X-rated safety capacitor. These combine a quite high breakdown voltage with special design and testing to make any failure less likely to result in fire or explosion.

And for line to ground applications, consider using Y-rated safety caps. Here, failure can put the juice where you really don't want it.

The safety caps are more expensive than DC-rated parts, but are still pretty cheap to buy.

See http://www.justradios.com/safetytips.html, or use Google to find out more.

The magic phrase to find these seems to be "Interference Suppression Capacitors"

Ted

AC line voltages are RMS. The peak voltage is 1.414 times higher.
A 600 volt DC capacitor's AC rating would be much less.

Pete

Another option you could explore is a TVS diode placed across the line. Of course when these radio's were built solid state devices did not exist and they sometimes used capacitors in a futile attempt to clamp spikes. You've seen the results with the one that exploded; there are better options.

Here is a 160 volt, bidirectional, single channel unit that should perform well.

http://www.mouser.com/ProductDetail/Lit ... 4h98SC8%3d

Interesting options were offered here to keep in mind for this particular part.

Your right , I try to use ac rated caps as much as I can or try to use real high voltage rated cap , so far never had any problems cross my fingers