Lynn wrote:

Anyone ever bother to check resistor values? During overhaul and repair
of lots of tube era marine electronics, many composition (and films
sometimes) resistors had changed value considerably. Especially those used
in voltage dropping circuits. High value resistors ( half megohm or more)
seemed to be pretty wild too.
Of course checking frequently meant disconnecting from associated
circuitry to check is a real
pain in the you know what, but the end result, (including the condenser
replacements) resulted in amazing results!
Anybody find similar resistor drift?

My general method is to check them all in-circuit with a DVM. The thing is,
resistors tend to fail by rising in value, rather than falling. And the errors
due to in-circuit testing all reduce the measured value (since there is stuff
shunted around them).

So, if the measured value is lower than it should be, I go on to the next
resistor. But if the measured value is more than 10% or so higher than the
value on the resistor, I'll replace it.

Sometimes I miss resistors this way, since if a much lower value thing
is across it, the test is useless. But it doesn't take more than a few
minutes it and catches a lot of them.

Things like plate resistors often are worries, because they are generally
pretty high values, they tend to get hot, and they are in a part of the
circuit where if they get noisy it'll be a problem.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."