[leftwing25]

Hey guys.  Ok, I know that resistors increase in value, but is it possible for them to decrease in value too? Hope I put this in the right place.  Thanks.  Ed

[morzh]

Yes, happens too. Have seen several cases.

[leftwing25]

Thanks , Morzh. Thought so, but have never seen one possibly till now. schematic says 300 0hms, meter says 150 ohms. Can't even tell what colors are on this thing. Old dog bone. Well it gets replaced anyway. Thanks again. Ed

[Arran]

Thanks , Morzh.  Thought so, but have never seen one possibly till now.  schematic says 300 0hms, meter says 150 ohms.  Can't even tell what colors are on this thing.  Old dog bone.  Well it gets replaced anyway.  Thanks again.  Ed

 It sounds like this 300 ohm resistor of yours was overheating, probably due to excessive current draw, that can cause the value to drift downward sometimes if it doesn't burn out entirely. The reason that many of those "Dogbone" style resistors go up in value is because the connection between the resistive element, and the outside world, is often just a wire wrapped around the end of a carbon composition rod, if it gets a bit loose the joint builds up a greater resistance. It also does not help that the materials used in making the rods were often unstable themselves.
Regards
Arran

[leftwing25]

Arran, thanks for the reply. Yeah I've seen them decrease with heat, but never permanently. I can't tell what the value is on it. the body is black, one of the ends looks like brown, but also looks like the body may have been painted black after the fact. No dot anywhere that I can see. Also this is in a bias circuit on a 6U7 that only draws 10ma at 6 volts. Don't know that that would cause an overheating problem. Anyway it's getting replaced. But something is pulling the B+ down about 70 volts in this chassis.

[codefox1]

I have also seen decreases in carbon resistors values due to cracking/arcing/grunge deposits. Replace the carbon resistors, they're cheap enough. Don't think that's your primary problem, though, assuming you have replaced all the filter and paper caps, sounds like a short in the wiring or a tube. Post a schematic or link with your findings and we'll take a look.

[leftwing25]

To all who responded to my initial question, thanks for the input. Much appreciated. Found the problem with the missing B+, but since this is not a Philco radio I am going to open a thread in the other radios forum to explain the simply solved problem (at least I hope it's solved).

[Warren]

hmm, come on Leftwing, you an ask us for input. We are also interested in what you think fixed the problem .

[mikethedruid]

hmm, come on Leftwing, you an ask us for input. We are also interested in what you think fixed the problem .

Warren, check out this new thread by him, http://www.philcoradio.com/phorum/showth...#pid103618

[Warren]

Ahh, cool thx. I understood he wasn't gonna tell us in this forum.