Re: Resistor in series


That's good information Menahem. Thanks for posting it.

I'll just add that I have a large number of 40-ish year old Allen
Bradley carbon comp resisters, many of them still in the factory sealed
packages. I have probed through the packaging and measured many of them and
they're ALL well out of spec! So don't trust old carbon camp resisters
even if they've never been used. Seeing how far out of spec that many of
these resisters are, it amazes me that any of this old equipment that uses
them still works!

On Mon, Nov 30, 2020 at 3:50 AM M Yachad <> wrote:

Choosing a substitute resistor type, as others mentioned here, is not a
simple matter.
You really need to know what its function is in the circuit.

Carbon Comp resistors are the only absolutely suitable choice, if the
circuit has current surges.
Film resistors of all types simply cannot handle the range of current

If you really cannot find a Carbon Comp (and the circuit requires it),
then a Ceramic MAY be a good substitute, and if you are still really stuck,
then the next possible substitute is a Metal Oxide type. BUT, Metal Oxide
starts to introduce inductance into the circuit.

Carbon Comps also have no inductance (inductance kills - as in obliterates
- performance in RF circuits).

Now, Ceramics come in two types - Inductive, and non-Inductive. Again, For
an RF circuit, ONLY a NON-Inductive is suitable.

Notice that I haven't even mentioned film resistors.
On these vintage machines, you really want to investigate using Carbon
Comp or Ceramics first, to solve the problems, without introducing new

Your choice was correct to use Carbon Comps, but I would recommend buying
new production pieces from Mouser or Digikey. Highly unlikely that you'll
find significant deviations due to moisture in cracks, or whatever..

Menahem Yachad

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