Help Identifying Resistor

Thread Starter

Ripley Rocks

Joined Nov 6, 2015
4
Hello all. I am having a really hard time identifying this resistor to replace in an amplifier. The amplifier is a Trace Elliot GP12 SMX. The back of the amp says 400W, 800W peak. The colors look to be brown red violet and silver to me. But I cannot tell. Some have told me that can't be right because the value is way too high. I will post pictures of it here.

The other thing is I have looked up the schematic for the amplifier and it says its a different code, but I see other obvious errors. Here is a Schematic that says it is for the Trace Elliot GP12 SMX 350-400W amp. It says the resistor would be 470k resistor. But it also looks like it says that both R24 and R23 are the same value, that is obviously not the case. Here is the link to the schematic:

http://hpbimg.someinfos.de/diy/allgemein/_schematics/amp-schem/trace-elliot-GP12smx-350-400w.pdf

I am looking for R25. The connector broke off of it and the dude soldered on a piece of metal to the short bit of metal left hoping to make the connection. I don't think it is working right. Which is why I want to replace because the amp is having problems. Want to make sure this is not the problem. Thanks for any help.



 

WBahn

Joined Mar 31, 2012
24,850
R23 and R24 look to be the same value to me -- they are just installed in opposite directions.

R25 looks like a (burned up color code) (violet) (red). That means it will be X700 Ω and the only standard value two-digit value that ends in a seven are 27 and 47. Resistors with 47 are much more common, so my bet would be that it is a 4700 Ω resistor (4.7 kΩ or 4K7).
 

WBahn

Joined Mar 31, 2012
24,850
How should we know?

Are we expected to analyze that entire schematic against a set of performance specs that we don't have to determine if using a 10% tolerance resistor instead of a 1% tolerance resistor would let it operate out of spec?

It depends one what THAT resistor is doing in that circuit and what is important. It could conceivably be that using a carbon film resistor instead of a metal film resistor (of whatever the original resistor is) could cause bigger problems than any increased absolute value mismatch.

My guess is that you will be fine. Most schematics or BOMs will give an indication if any particular characteristics are abnormally important.

To hedge your bets, take the five resistors you get and use the one that is closest to the nominal value.
 
Look at R23, R24

Violet, Yel, Red, brown or 4720 ohms. Not 47K Measure them out of circuit.

4 band resistors can be tricky. I get 4.7K 1%

R22 and R24 are the same color code wise. I don't get 470K.

R26 could be 4.7K 1%

maybe, they mixed them up on the BOM.

So, I'd check the other resistors of the "same value". I'd also look to see if the solder has been disturbed.
 

WBahn

Joined Mar 31, 2012
24,850
Look at R23, R24

Violet, Yel, Red, brown or 4720 ohms. Not 47K Measure them out of circuit.

4 band resistors can be tricky. I get 4.7K 1%

R22 and R24 are the same color code wise. I don't get 470K.

R26 could be 4.7K 1%

maybe, they mixed them up on the BOM.

So, I'd check the other resistors of the "same value". I'd also look to see if the solder has been disturbed.
4.72 kΩ is not a standard resistor value (even in the E192 series).

Then again, strictly speaking 4700 Ω is not in the 2% (E48) or 1% (E96) sequences, either (it does, however, reappear in the E192). But with 1% resistors being so commonplace today, many manufacturers are simply selling 1% resistors in the E24 sequence values to address concerns (mostly needless) about issues when using a slightly different nominal valued resistor.

Although there is certainly some annoying variants here and there, my understanding is that a four band resistor has two value bands, a multiplier band, and a tolerance band. So this would be a 4.7 kΩ ± 1% resistor. If it were a 4720 Ω 1% resistor it would need a fifth band (another brown band) to indicate the tolerance.
 
Well, here's http://www.digikey.com/product-detail/en/RNC55H4721FSB14/RNC55H4721FSB14-MIL/3236574 a 4720 resistor.

Here http://www.digikey.com/-/media/Images/Marketing/Resources/Calculators/resistor-color-chart.jpg?la=en-US is a chart for 3 digits and a multiplier.

The OP wanted "help". I've run into 3 significant figures and a multiplier when I ordered metal film resistors to build my amp in the mid 80's.

There are 14 resistors that are 47K.

R15 and R18 are 33K. That one has to be an easy one to figure out. Orange Orange something.

Assume that the resistors came from the same manufacturer and try to deceifer the code. You should be able to tell an order of magnitude anyway without taking the resistor out of the circuit.

Once you get the 4K7, 47K and 470K sorted out. i.e. Just make sure all of the resistors in the group are in the right ball park knowing the circuit around them, Reverse the leads of the meter when measuring too.

the OP said:
But it also looks like it says that both R24 and R23 are the same value, that is obviously not the case
As was said earlier. They are the same value. They are not installed the same way.

Something isn't right, so measure. All you really need to worry about is the "order of magnitude" with and without the leads reversed.

The 33K resistor should offer a LOT of clues especially if it measures "in the ballpark".
 

WBahn

Joined Mar 31, 2012
24,850
Good to know.

Yes -- three digits and a multiplier PLUS a tolerance band making it a FIVE band resistor. The resistors in the picture are FOUR band resistors.

The OP wanted "help". I've run into 3 significant figures and a multiplier when I ordered metal film resistors to build my amp in the mid 80's.
And did those resistors lack a tolerance band? If not, then they were five band resistors, which is NOT what is shown in the photos.
 
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