[Hallicrafters] Speaking of Resistors

[Richard Knoppow]

-----Original Message-----
>From: Robert Sauvan <rsauvan at beyondbb.com>
>Sent: Jun 4, 2014 5:34 PM
>To: Hallicrafters <hallicrafters at mailman.qth.net>
>Subject: [Hallicrafters] Speaking of Resistors
>
>Hi all,
>As you are all aware, we had a very good education in checking and 
>replacing resistors last week. I put the SX-101 back in service and am 
>finding it to be working quite well up to this point. I have now brought 
>the HX-50 onto the workbench to try to locate the chirp I have in this 
>rig. I know its not Hallicrafters, but Im sure all of you are familiar 
>with this unit. So, I started troubleshooting and decided to start 
>checking resistors after my lesson from last week. One particular 
>resistor in the K101 relay looked to be somewhat suspicious. It had a 
>kinda shiny surface and very very small bubbles or bumps on the surface 
>so I decided it must have gotten hot at one point. The manual called for 
>a 47K
>2 watt resistor in this circuit. The bands on the resistor in the radio 
>indicated it was a 41K. When I put my meter on it, it showed about 54 
>ohms. Wow, it was way high as I was told bad resistors will show as they 
>get old and in a circuit. I picked up a new resistor today with the 
>correct spec as the manual indicated it should be. I cut the old 
>resistor out and rechecked it. It measured almost 58 ohms out of the 
>circuit so it is definitely bad. I replaced it and fired up the rig and 
>my oscilloscope shows a nice waveform. The waveform previously had been 
>a bit skewed so I dont know if that is what a chirp looks like on the 
>scope or not. I have not monitored the signal as of yet because my shack 
>is a bit far away to hear it in one of my receivers. I have ordered all 
>new electrolytics for this radio since I have the case open and plan to 
>replace them since it would be a good time. They should be here tomorrow 
>so I will replace them and put this thing back on the air and see if I 
>get any more 579"C" signal reports. Lesson well learned and executed.
>
>We thank you-Bob-W0YBS
>__
      This is very unusual.  Mostly carbon composition resistors go high in value, occasionally doubling. I can't remember ever seeing one go low. This one sounds like it developed a partial short.  I understand something of what makes them go high but can't figure out how this happened. I wonder if this is actually a low value resistor someone put in.  Check the color stripes again. If the thing got seriously overheated it may have affected the colors. Let us know what you find.