Resistor Tolerance on Old Audio Amp

[Bskitter]

Hey Guys I am servicing my old Kenwood Amplifier and I am looking for resistor replacements.

I currently am looking for 0.33 Ohm 3Watt 5% Resistors,

I can get these resistors on Ebay but with a 1% tolerance,

Would these Ebay ones be a suitable replacement or was the amplifier designed with the 5% tolerance of the resistors in mind ?

Regards

Byron

[JS]

Yes, no problem at all. The only motive to go to a worse tolerance is price, if price is not a problem and you can get easier the better tolerance ones go for it. You still need the same power rating though.

JS

[Zero999]

Tolerance is just a percentage of how much the actual component will differ from the specified value. In the case of a 5% resistor, 5% of 0.33Ohm is 0.0165Ohm, so the resistor can range from 0.33-0.0165 = 0.3135. to 0.33+0.0165 = 0.3465.

1% of 0.33Ohm is 0.0033Ohm, so if you repeat the above calculation, the range of values is smaller.

In short, as mentioned above, yes you can use a 1% tolerance parts in place of 5% tolerance.

[Audioguru]

Many electronic parts sold on ebay are no-name-brand rejects. Isn't it best to buy good parts locally instead?

[Brumby]

The amplifier design allowed the use of resistors that could be up to 5% off the specified value.  For example, if a 1k resistor was specified, the one used could have an actual value of between 950 and 1050 ohms and the circuit will work as designed.  So getting a resistor that is closer to the nominated value is going to be completely fine.

As for getting them off eBay, you need to be careful.  As mentioned above, you can come across rejects - which may or may not be a problem.  For example, a couple of years ago, I got a really cheap 'grab bag' of 1% resistors - but when I checked their values, they were a bit off....  They were more of +0/-2% than +1/-1%.  Fortunately, this wasn't really a significant concern for my needs.

The point is that you can't really be sure until you get the components and check them out.

[ebclr]

"Many electronic parts sold on ebay are no-name-brand rejects. Isn't it best to buy good parts locally instead?"

This is not true

maybe some, not many

[retrolefty]

"Many electronic parts sold on ebay are no-name-brand rejects. Isn't it best to buy good parts locally instead?"

This is not true

maybe some, not many

 Agreed, it's become a meme that fails to keep up with reality.   

[obiwanjacobi]

Perhaps a good idea to update ALL resisters (in the power stage) to make sure no (minor) inbalances are introduced...?

[tooki]

But (assuming it's not fake) the 1% tolerance is within the tolerance of the original. If the design required matched pairs, they'd either be specially marked, or would be lower tolerance.

[ciccio]

In audio amplifiers these power resistors are usually the power transistor's "emitter degeneration" ones.
They usually burn when the output transistors fail.
Tolerance does not matter. When buying from an unknow source, check all of them with an ohmmeter. Sometimes the label is wrong..

[CatalinaWOW]

There is a remote chance of a problem.  There was a period when toleranced resistors were produced by selecting from a large population with a fairly wide distribution.  Up through sometime in the 1960s I think.  If a vendor offered 2%, 5% and 10% resistors, when you purchased 10% you could be reasonably sure that none were within 5% of nominal, and if you bought 5%, none would be closer than 2%.

As resistor fab processes evolved, vendors could produce lots of resistors within the tighter tolerances they offered and this selection process stopped.  The control over resistance values has gotten so good that the larger tolerances are no longer available, as you have discovered.

If your Kenwood is from the 1960s or maybe even the early 1970s, and you want to be totally anal, you could purchase your 1% resistors 3% off nominal to assure that they were within the range originally validated by the designer. 

I would stick with putting the nominal 1% resistors in.

[Bskitter]

Hey Guy !

Thanks you for all the advice,

I bought these, and ill test them as soon as they arrive !

Byron