HW100 nightmare

[Herman N4Ch]

Something that's very quick and easy to do (and  safe........you do it with 
the radio powered down and unplugged) regarding  finding the cause of 
problems such as low drive, poor sensitivity, an oscillator  that won't start, 
inability to get PA idling current to where it should be,  etc., is to use a 
simple auto-ranging digital multimeter, and simply go thru a  quick exercise 
of "ohming out" all those old resistors in your  transceiver.   Keep a roll 
of masking tape handy, and whenever you  find a bad resistor, mark it with a 
piece of tape, and then replace the bad  resistors once you are done going 
thru the rig with the DMM.   It's  amazing how many out of tolerance old 
resistors (that look just  fine......no sign of ever overheating, etc.) I've 
found in old Heathkits, Swans,  Drakes, and many others.   Often they will be 
2-3 times the resistance  value they should be, with the higher-wattage ones 
(1 and 2 watt versus 1/2  watt) being the biggest offenders.   The larger 
wire-wound types  seldom have this problem........usually when they go bad, 
they are  open.    The old carbon composition resistors can climb in value  
significantly even if they are never used..........I hate to think about  how 
many virgin, never soldered to, straight-leaded NOS resistors I've  pulled 
out of the parts bins to use, only to find they had twice the number  of 
ohms they should have had.   When you replace resistors, consider  the newer 
film types.........my experience is they don't "drift" upward in value  like 
the old composition types do.   Just last week, I went thru an  old Swan 350 
that had poor receive sensitivity and low output.........and I  found 10-12 
resistors that were at least 50% high in resistance, and over half  of those 
were 1 and 2 watt ones.   Replacing them fixed all the rig's  issues.   
Resistors are simple to check and cheap to replace, and I  bet you will find 
several in that old HW-100 that have climbed high in  value.   Good luck.
 
73, Herman, N4CH.
 

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