Resistor precision in SX-850 power supply board

[Big Ben]

I need to replace R9 on my SX-850 power supply board (Resistor is ok, but I cut the lead too short by accident). The service manual describes it as a 18k Carbon Film PS-183J, 1/4w.

My question is what precision should I pick for the replacement? The colors bands on the resistor are brown, grey, orange, gold, which I decode as 18k, 5%, but then there is a 5th blue band.

The resistor measures at 18001 ohm. This could be that this is just very lucky for for a 40 year old 5% part, or do I decode the color code improperly, and this needs to be a more precise part?

 

[Big Ben]

Thanks for confirming. I’m still curious about the meaning of the 5th blue band though

 

[EngineerNate]

I buy 1% metal film resistors exclusively. They aren't expensive.

Most SMs will have a note at the top of the parts list saying something like, "All values +-X% unless otherwise noted."

 

[llwhtt]

Fifth band is Temp. Coeff, blue is 10ppm/k

 

[Big Ben]

Looks like it’s going to be challenging to find a suitable replacement then... 10K/ppm resistors seems pretty uncommon (unless you want to order several 1000s of them and wait a few weeks).

 

[LesE]

Hmm ... I thought that only Metal Film types (RS) used by Pioneer were spec'd for temp coefficient.

R9 is a carbon film resistor (RD type - RD1/4PS 183J). The Tuning Fork doc says the following regarding RD resistors:



This doesn't necessarily mean that you need a low noise resistor here. It could be that this supplier designated all of their resistors as low noise.

 

[Big Ben]

Ah, that makes more sense... Unfortunately the same tunic fork guide doesn’t seem to specify the noise spec for low noise carbon film resistors (only 25 dB for standard resistors). That being said, the spec on the random carbon film resistors I got says 0.15 microV/V, which would be 67dB, if my calculations are right, and the measurements are made using the same method...

 

[LesE]

Personally, I wouldn't get too hung up on this. If this was a phono stage I might be a little more concerned but this is a power supply. I'd just go with a standard 18K ohm 1/4W 5% carbon film resistor.

 

[Big Ben]

Yeah, I guess I’m overthinking this . Thanks everybody.

 

[llwhtt]

That's 10ppm/k, 10 parts per million/ Kelvin. Just use a 1/4W carbon film or metal film.

 

[EngineerNate]

If you're concerned about noise, the Vishay Dale RN55/60 series are about as good as you'll get without going to a thin film resistor.

 

[avionic]

4th band is tolerance band ---- gold = 5% , silver 10%, no band 20%

 

[avionic]

PS-183J

J anotates 5% as well.

 

[rcs16]

I use Yaego MFR-25F series usually, from Mouser, since it is so well stocked and has a few options for each value, you can always seem to find one that is in stock.
They are stocked in E12 & E96 series values
5% resistors are of little value these days for new designs, since precision resistors are about the same $.
Dale and KOASpeer are good too.

 

[EngineerNate]

I use Yaego MFR-25F series usually, from Mouser, since it is so well stocked and has a few options for each value, you can always seem to find one that is in stock.
They are stocked in E12 & E96 series values
5% resistors are of little value these days for new designs, since precision resistors are about the same $.
Dale and KOASpeer are good too.

Those are nice too. Their half watt rated versions are quite compact.

 

[rcs16]

I have a DH-220C design I just did up, it was really tight, used Vishay SFR16S, in some places. We used them years ago with Motorola 10KH ecl designs. Originally a Philips part, a bit more $ and not as well stocked at Mouser.
10ppm/k, is an exceptional value, I would not think a carbon film could ever perform as well
T/E(Tyco) YR1B are good
https://www.mouser.ca/Passive-Compo...Z1yzrmcwZ1z0wdwsZ1yzrlxyZ1yzbpod&Ns=Pricing|0
are the best that Mouser has for a leaded 18K,1/4w = total over kill for the application.

 

[EngineerNate]

Yeah if the original is a carbon film there's no way it means 10ppm/*C.

 

[rcs16]

More like 100ppm which is still very good. Not too many mfgs use colour coding for tempCo any more, it was a mil spec requirement in the past, I assume.