[Hallicrafters] Speaking of Resistors

[Robert Sauvan]

OOOPS,
Sorry, I left the "K" out of the 54 and the 58 in my writings.. They 
were actually 54K readings and 58K readings which were high compared to 
what the bands on the resistor showed as a 41K valued resistor. The 
manual calls for a 47K so it started out low to begin with but with plus 
or minus specs it worked OK. I replaced it with the 47K as the manual 
reads. But 54-58K is way high I would think?

Bob-W0YBS




On 6/4/2014 6:41 PM, Richard Knoppow wrote:
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> -----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.
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