The PHILCO Phorum
Resistors - Printable Version

+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Electronic Restoration (https://philcoradio.com/phorum/forumdisplay.php?fid=8)
+--- Thread: Resistors (/showthread.php?tid=10400)


Resistors - OldRestorer - 08-31-2014

Ok I am getting back into these chassis and am lost with these resistors.

Reading resistors:
You can see the 3 resistors in the picture above. I know 2 are 490'000.00 and the other is 240'000.00 by looking at the schematic but how do you tell on the resistor? The 490K body is yellow and the end is white but no dot? Same for the 240K. red body, yellow end but no dot? Is there a different way to read them?

Next is this:

I measured the 51'000.00 51K and got 58.8. Is that too far off? What is the percentage again? I looked online and see a lot of 20% so I just want to make sure.

I remember someone saying to remove one end before checking resistors. Then someone told me it was a waste of time.
what do you guys think?

Also I measured a 10'000 watt resistor but it is coming up 9'500. One or 2 others are also coming up lower. Is that normal? Does the 20% work both ways?

Lastly, I purchased all the resistors of common values but none of these really are the same. I have 10K but no 49K. All I have is 47K.

I need an exact duplicate right?

Sorry for so many questions but Resistors are something I barely learned and then I stopped doing chassis for the last few months since Mike was doing them for me.

Thanks for any guidance

Kirk

RE: Resistors - Steve Davis - 08-31-2014

When the dot is the same color as the body, you can't see it.
Red body, yellow end, no dot would be 2.4K

Steve

RE: Resistors - morzh - 08-31-2014

Kirk

58.8K will likely work fine where 51K is supposed to. However if you solder around it, after you done re-measure as soldering exacerbate the value drift. If it did not change you could leave it, if after soldering around it went up another K or a few, change it, as it will get worse. progressively.

One school of thought is, change them all as they will eventually drift outside the acceptable (you and I will probably not be alive to see it but our descendants will curse us).
I do not subscribe to it, but it buys peace of mind, it does.

RE: Resistors - David - 08-31-2014

Resistor tolerance is +or- so on the 51K plus 10% equals 56.1K minus 10% equals 45.9K. If I have to remove one end of a resistor to measure its value no matter the reading I will replace, because of possible damaged caused my me!!! On your 49k measure your 47K if the reading is between 44.1K-51.7K will work just fine. The 44.1K is 49K minus 10% the, 51.7 is 47K plus 10% the reason for not using 53.9K if that was the reading from the 47K it would be out of 10% tolerance range. When working on old radios I replace resistoes that are out more than 10% even if the orginals allowed +- 20%. They are cheap and only want to fix them one time. Some radios you will replace most others very few. Hope this helps David

RE: Resistors - OldRestorer - 08-31-2014

Ok so I get most of this but what about replacement?

I dont have any 490K or 240K resistors I only have 470K and 220K.
Do I need to order the correct ones?


Kirk

RE: Resistors - exray - 08-31-2014

Go to for a Philco 490k would be the common 470k. If if you want to be picky 510k can be had. 240k is plenty available. Alternatives are 220k and 270k.

Back before standardization resistors came in block numbers like 25k, 5k, 50k, etc. The modern system is staggered so that each 20% value meets the other and so on.

Add to that that Philco had an adversion to black bands as a help to the assembly people due to poor lighting. So 100k resistors were often painted as 99k, etc.

RE: Resistors - morzh - 08-31-2014

Yeah I was wondering what the deal was with these 99K.


Kirk, you could measure most resistors in tube devices without desoldering one end, as more often than not the only things that parallel the resistor would be either a tube electrode or a cap, and neither is a DC load, so a resistor should likely read its value when buzzed in-circuit.

Unlike in solid state devices.

RE: Resistors - Warren - 08-31-2014

490k - 10% = 441k
240k - 10% = 216k

So, as long as they are above that should be ok.

RE: Resistors - OldRestorer - 09-01-2014

Ok I am getting it...

So the 470 is ok to replace the 490 since it is within the 10% spec.

Thanks!

Kirk

RE: Resistors - codefox1 - 09-01-2014

If you are replacing all the old paper capacitors in a simple old set, makes some sense to replace all the carbon resistors at the same time seeing as you have cleared off the terminals and so on. A fist full of resistors is only a couple of dollars, and as already stated, best fix up a set once. Carbon resistors generally drift up in value, but also develop "noise," and become heat sensitive as they age. De-soldering can, as mentioned, make them less stable. Your choice!