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Author Topic: HAMMARLUND HQ-129X RESISTOR COMPOSITION  (Read 692 times)
AC0FA
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Posts: 298




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« on: July 29, 2007, 01:20:21 PM »

Hello all.
I finished re-capping the hammarlund early this morning. I came accross something unusual in the the tube socket for the BFO. The one that has the can around it. I removed the can to replace the Bees Wax Capacitors they looked fine. I found a ball of peanut butter colered wax in the bottom of the can about the size of a resistor.

Uppon Closer inspection I discovered nothing but two wires sticking up from where the 10k resistor would have been attached.

This leads me to believe that some of original resistors in the rig from 1947 might be something other than ohmite.

Are Some of these resistors just made out of wax? and just melt.

If so I will just replace the fuzzy peanut butter looking ones with ohmite.

Any Ideas?
John AC0FA    
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KA5N
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Posts: 4380




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« Reply #1 on: July 29, 2007, 02:43:30 PM »

The wax oozes out of the capacitors over time.   I suspect a glob of wax just happened to land on the wires.  They didn't make resistors out of wax.  Someone may have clipped the resistor out and left the wires or the resistor body could have crumbled away.
Some old resistors look funny and have funny markings, but all the resistors in the HQ-129X should be the same type with maybe some wirewound power resistors.
Allen
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KE3WD
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Posts: 5694




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« Reply #2 on: July 29, 2007, 03:26:51 PM »

Beeswax was also commonly used up in the coil, too, to insulate and hold wires in place and to keep slugs from moving after adjustment.  A small amount melted out of there or the capacitors over time and heat can be ignored.  

Would have to believe that all resistors in a piece of that age would be carbon resistors.  Carbon can and will absorb moisture over time, changing the value of the resistor.  Best way to check is to unhook one lead of each resistor and measure value with ohmmeter, then see if the measured value is within the tolerance limits for the band value.  Gold = 5% tolerance and Silver = 10%.  Perfectly okay to replace with modern resistors of the correct wattage.  Metal film 2% resistors for the purist, 5 or 10% resistors available today should do fine.  

If you see no black powdery residue or flash mark, I would doubt that there was an old carbon resistor in that place that suffered a catastrophic failure.  Those old thangs would mark their spot, man.  

Examine the ends of those two leads closely, even magnified if you have too, if you see the telltale marks of the diagonal cutters, then you will know somebody clipped it out of circuit.  If, on the other hand, you see two squared and clean ends on the wires, and maybe what looks like a collar around the wire the exact distance from each end on both, suspect that there was indeed a resistor there, although some savvy tech may have done the removal by first clipping the resistor body itself with the dikes...  


HTH,


.
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AC0FA
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Posts: 298




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« Reply #3 on: July 29, 2007, 03:57:30 PM »

Ok, thanks for the info.
I did see the collars on the end of the wires and no carbon chips in the can.

So, someone intentionally diabled the BFO.

Any Ideas as to  why?

I will be using it to receive AM signals on the ham bands. Maybe the bfo was making to much noise even with the selector switch on a diferent position?

John AC0FA  
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KE3WD
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« Reply #4 on: July 29, 2007, 07:19:46 PM »

This is where a resitance substitution box is a very handy item, clip it to the leads after dialing or switching in the specified resistance and fire the rig up, observe its behavior.  

Of course, without the substitution box you could just tack solder a resistor of the right value there and do the same thing.  

Those rings on the leads may or may not mean somebody took the resistor out by cutting its body:  it may have suffered a catastrophic failure and there may not be any evidence of such in there, so be careful.  Measuring the voltage between the two leads and making sure that it isn't some overly huge voltage might be a thing to do, just in case.  But won't always guarantee you don't perhaps have a current problem.  


.
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AB3CX
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Posts: 621




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« Reply #5 on: August 03, 2007, 10:48:38 AM »

I repair alot of old radios from the 1930-1940 era. Any resistor can burn up, dogbone or otherwise, especially when it is drawing too much current. That commonly happens when a capacitor shorts to ground beyond it, causing a voltage drop, increased current draw, it overs it's power rating, and the resistor overheats. PFFFFT.
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OLDSWAB
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« Reply #6 on: August 06, 2007, 12:18:32 PM »

Sounds to me that you have a old resistor missing that was of the type that was a bar carbon with the wires being the ends of the resistor. Have you tryed to find a print on that radio?  Try baha or just try just putting in the radio model and schemetic.. That would help you find out a little. I have a very fiewof the old resistors and the wires are solid attached to the bar.  Hope this helps.
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