Help sourcing two resistors

Thank you. I find a 1% and a 5%, but not a 20%.
Is it acceptable to use a smaller % in place of the 20%?

The symbol is a measure of tolerance. The smaller the better. A resistor with 20% tolerance would be plus or minus 20% in ohms value.

If you measure resistors in circuit, the reading you get can be lower because of other components on the board.

Please tell us the outcome.

hotrodjohn71 said:

Hi group.
Can you help me source 2 resistors I need for my 57 Ford truck radio?
Ive searched for about a half hour but am coming up short.

One is a 680k 20% 1/2 watt
And one is 15M 20% 1/2 watt

Thank you

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20% resistors are not made anymore and the circuit would operate better with the modern lower tolerances.
But I doubt the resistors are bad in the first place because they are grossly oversized in the first place wattage wise so the resistor's Johnson noise is not predominate in the circuit to be amplified.

The only way to test resistors is to lift one leg and test it out of the circuit. the one only measuring 210 ohms might have a transformer winding in parallel or even a potentiometr in parallel.

Which one is it?
The model number is usually stamped on it, sometimes in a corner. But looking at your pictures I'm going to guess its a 75MF. Someone will have a schematic of this as these things did come in the TV repair shop to fix every once in a while. So its either in the Bettman or the Sams photofact manuals.

drtechno said:

20% resistors are not made anymore and the circuit would operate better with the modern lower tolerances.
But I doubt the resistors are bad in the first place because they are grossly oversized in the first place wattage wise

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Possibly not, old resistors, and particularly high value ones, were notorious for drifting high in value - or even going O/C.

Obviously 1% resistors would be perfectly fine as replacements, but it's unlikely the circuit will operate any better, as it was designed to use 20% tolerance parts.

However, it's obviously dead easy to test them, lift one end out and check on an ohm meter - but while you're unsoldering one end, you may as well unsolder both and simply replace them with more reliable modern resistors.

Did you contact digikey?

Yes. I have the resistors coming. Thank you for the reference.

This is a 1957 Ford truck radio. I found the diagrams online through a group called Radio Museum.

I am a novice in electronics so I appreciate the advice.

There is a guy who did a rudimentary srep by step repair of the radio that has been a big help.

He stated that there werent any parallel circuits so I didnt remove the components to test them.

I also have a working radio that I did component by component testing side by side.

Im awaiting the resistors with high hopes.