rca: RCA 103

I am looking at the scematic of model 103 and see listed all the different capacitors. They all list the mfd value but no voltage. Is there a way to determine the voltage specs when they are not apparent on the capacitor itself?  Thanks for your help to a newbie in advance.  Regards, Les

 

So, once again, is there any way to tell the voltage of a particular capacitor by looking at the scematics? Even the parts list on this model do not list the voltages. What if the capacitor has been damaged and the voltage scraped off? What then. Thanks, Les

 

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Usually those who somehow are connected to positive voltage should be 400 V, electrolyte and in the process.

C1, C2, C3 can be 100 V.

C19 can be of 63 V.

regards

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Greetings Les.

I agree with Francisco's advice, but you may find some paper capacitors rated at 600 volts.  One thing you may want to do is check the marking of the existing capacitors in the radio.  This may mean melting away some of the old wax to read the printing on the paper.  A soldering iron on a low temperature setting may help with this.

Before you purchase capacitors, consider a few things.  In your profile, you mention that you want to repair and collect radios.  If you acquire a good size collection, you will indeed be replacing many capacitors.  For that reason, you may want to purchase capacitors in bulk to save come cash and to have a stock on hand.  I do this, and while I used to stock multiple voltage ratings for a single size capacitor, I now fill my stock of common size capacitors with only 630 volt rated capacitors.  It is cheaper for me to buy 100 pieces of 0.01uF @ 630 volt capacitors than 25 rated at 630 volts, 50 at 400 volts, and 25 at 200 volts.  When I say common sizes, I'm referring to sizes such as 0.01uf, 0.02 uF, 0.05uF, 0.1uF, etc.  I think there is a 0.017 uF capacitor in the tone control circuit of your radio.  You may want to use a 0.02 uF capacitor for that since 0.017 uF is not a common size.

Don't forget to read Replacing old capacitors with many great ideas from other members.

We look forward to hearing from you.

Howard

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Les, I'm going to answer your questions individually with what I hope is a helpful explanation.

Q: "So, once again, is there any way to tell the voltage of a particular capacitor by looking at the scematics?" 

A: In this case, the voltage ratings are not stated in the schematic, therefore, an educated judgement needs to be made.  That is what Francisco did when he created his post, and I agree that the voltage ratings he specified are sufficient.

"Even the parts list on this model do not list the voltages"  True.  Some schematics or parts lists contain voltage ratings and give detailed part information while others do not.   I would be inclined to believe that RCA wanted the individual repairing the set to purchase only RCA parts using their stock number.

Q: "What if the capacitor has been damaged and the voltage scraped off? What then"

A: I would recommend using the highest rating that I typically see in a set of the same vintage and using the tube types you have.  I don't recall ever coming across a capacitor rated higher than 600 volts on a mid 1930s RCA superhet, so if in doubt, I'd go with 600 volts.

I would advise to keep in mind that replacing a capacitor that was originally rated at 180 volts with one rated higher, say at 630 volts, will not adversely affect operation of the set.  If one were to replace a capacitor originally rated at 600 volts with one rated at only 180 volts, it is likely that it would prematurely fail and possibly cause component (tube) damage or an unsafe condition.

Also be aware that the voltage rating marked on the capacitors is the DC voltage.  Introducing AC (including audio and radio frequencies) into the component lowers its voltage handling capability.  It is for that reason that it is not possible to measure the DC voltage across a capacitor and derive a voltage rating from a measurement alone.

I hope this helps.
All The Best,
Howard

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