11-11-2019, 10:47 AM
(11-11-2019, 09:42 AM)Bushbaby Wrote: but they are a deep mauve body colour rather than brown so I'm not sure of the manufacturer but will measure to see how they have stood up to time too.
These sound more like Piher carbon film rather than carbon composition (a closer picture would help). If so, they will probably be within spec. If any are out of spec, I wouldn't necessarily jump to replace them without first considering what they are doing. Few audio circuits are all that demanding, and in many cases, the usual 30% or more drift that you can get from carbon-comp resistors is not an issue. Occasionally it might matter, but as I say, it's worth thinking about it before replacing. If nothing else, the thought experiment might be a useful learning exercise.
One exception to that - when you have high voltages across high value film resistors (say, >100V and >100k), then they can go high or open-circuit. I explained my understanding of the failure mode a few years ago: https://golbornevintageradio.co.uk/forum...8#pid46468 (post #14 if the link doesn't take you straight there).
If this was a transistor radio or something that ran on similarly low voltage rails, then Piher carbon-film resistors have an excellent reliability record, as well as being really rather beautiful to look at.
