Value drift over time

No, those resistors have drifted since their original construction. People did have ohm-meters back then and would verify values on resistors particularly if they were colour deficient or colour blind as I did, testing Rs when building kits - red/green deficient vision. I still check almost all resistors I come across with a meter as I don't trust my green, dark red, and brown differentiation.

If they are in power circuits - plate or cathode or voltage dropping then those do drift as they were only compressed carbon and heat/cooling cycles would cause them to change value - usually upwards as you have discovered. I consider your values typical of tube gear that is 40 or more years old.

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...

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 :-#)#

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Reply to
John Robertson
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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.

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

NT

Reply to
tabbypurr

May seem counter-intuitive, but hydrogen is not actually the smallest atom. Heliums come singly alright, which is one of the reasons, along with small size, they're used for this kind of leak testing.

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Cursitor Doom

Good point; also, the H2 molecule has two 1S-like electrons, which is very similar to a Helium atom, and just about as slippery. H2 atoms are lighter than He, on average.

Reply to
whit3rd

Good point; also, the H2 molecule has two 1S-like electrons, which is very similar to a Helium atom, and just about as slippery. H2 molecules are lighter than He atoms, on average.

Reply to
whit3rd

Thanks, I did mean composite.

Ads in the early radio magazines are handy for that sort of data. And yes, you did keep a drawer of grid resistors handy if you wanted best performance out of your rig.

Power derated curve curves can be surprising for almost any component.

Heck Molex pin connectors are rated at 25 insertions if I recall correctly, and they are heavily used in arcade games...

Spec sheets do need to be read after all.

John :-#)#

Reply to
John Robertson

Hydrogen is also explosive or will burn. That is another reason not to just spray it out for leak detection.

I think that hydrogen may be the smallest atom, but they often join in pairs to make up a larger molicule. Some other atoms that are normally gas do the same thing.

Reply to
Ralph Mowery

Oh boy. Where do I start?

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