[Hallicrafters] Resistance to change?

[Craig Roberts]

I've been restoring old tube-type radios for about 15 years (including some well-known museum exhibits) and found resistors -- generally -- to be stable and within specs when almost all caps have failed.  

There are exceptions, however.  Resistors in power supplies, subject to greater heat and heavier currents, tend to fail a little more frequently than those in other circuits. It's only logical, of course. I usually change power supply resistors when I upgrade the caps, but that's rarely actually necessary. It just feels more comfortable to me since, with new resistors, I know I'll be getting the right voltages to the right places at that stage.

Sometimes -- though rarely and very mysteriously -- many resistors in a rig will be out of spec (it seems to be all or nothing). I just had a Hammarlund in that strange condition. Significant numbers of the carbon composition resistors read high (which is usually how they fail). I replaced them (probably a dozen or so) with very high quality Ohmite ceramic composition types and feel confident the radio will outlive me handily.  Carbon comp resistors, by the way, are the most vulnerable type. 

I cannot recall a good, old resistor failing in NORMAL service after a rebuild. If it's okay now, it tends to stay that way, just as Duane's friend suggested. In another ten years, however, things could change (more about that in a minute). Everything ages.

Capacitors, of course, are a different matter. Multi-section electrolytics, for instance, are notorious for failing one section at a time in service -- especially if one of the other sections has been replaced.  And, as for Black Beauties, Little Chiefs, Bumblebees, etc. --- fuggedabboudit!!!  

Oh yes, one other thing.  For years we've been told that mica and ceramic caps seem to last forever.  Well -- that's no longer a truism. While unmolested ceramics are holding up, micas from the 50's and even the 60's are now starting to go "soft" in significant numbers. If you've got mysterious instability problems of any kind, think about replacing those "postage stamps".

73,

Craig
W3CRR