On Monday, 20 May 2019 13:40:53 UTC+1, John Robertson wrote:

1920s resistors were a chunk of carbon rod with a wire wrapped around
each end then dipped in a sealant - how long do you think that value
would last within X%? Wire wound resistors external connections were
pressure bonded to the resistance wire, not uncommon for that joint to
fail over time...

I presume you mean carbon composition rod. Pure carbon would give too few ohms to have much use in a valve radio.

Some Rs used metal caps instead of wires, and were mounted in a clip-in holder. I guess they needed to be replaced sometimes as different valves sometimes needed different grid leak values.


Like I said earlier you HAVE to verify all the resistors as they wander
over time. Modern Rs are much more reliable when operated under their
rated wattage.

John :-#)#

as long as it's well under. Rated life for power Rs operated at specced power can be terrible.


NT