06-01-2014, 09:32 PM
Body-end-dot code resistors, especially the dog bone style, are notorious for drifting upward in value. If you look at the construction they are basically a solid rod made out of a carbon composition material with a wire lead wrapped around either end. I think that the drifting may in part be the carbon composition and in part the contact between the leads and that rod building up resistance. Why some would drop in resistance could only be explained by the composition material becoming less resistive with age.
In the case of something like a Philco model 80 or 84 it's a four tube set, so every part that drifts or fails has that much more impact on the performance of the radio then in a set with a higher tube count. So I'm not surprised that replacing most of the resistors is necessary to get the set to work, there is just no redundancy in a 4 tube set. When these resistors were originally produced I believe that a a tolerance of + or - 20% was the norm, so the circuit could handle at least that much deviation, but + or - 50% or 100% no.
Regards
Arran
In the case of something like a Philco model 80 or 84 it's a four tube set, so every part that drifts or fails has that much more impact on the performance of the radio then in a set with a higher tube count. So I'm not surprised that replacing most of the resistors is necessary to get the set to work, there is just no redundancy in a 4 tube set. When these resistors were originally produced I believe that a a tolerance of + or - 20% was the norm, so the circuit could handle at least that much deviation, but + or - 50% or 100% no.
Regards
Arran
