Query - when to replace resistors

[Geaney]

I did some checking of the resistors on my current PYE project and just about all of them measure much higher than their rated values. What's the general view on how high they can go before they should be replaced? Clearly if a resistor measures double its nominal value I'd replace it but where should one draw the line in terms of percentage increase in value before replacing.
Thanks, John

[Mark R]

John
I usually work on the 20% either way of the original value.

cheers Mark

[beam me up schottky]

My view would be if they have changed their value by more than the marked tolerance they should be replaced. Obviously some are going to be in more critical circuit locations than others but considering that most older resistors in valve sets were 20% tolerance anyway, exceeding that is enough to seal their fate as far as I'm concerned.

[tiv48]

personly in valve gear itend to allow 15% some times 20% depends on what the do remenber most corbon resistors in vintage radios were +-10% anyway also because they used e12 values they chose the nearest preferd value.not much help i know
voltage readings will give a good idea of what need changing . the lower the value the more inportant the value is near. all this is in my opinion only others will dissagree
rob t

[Shaman]

Hi, a lot of production, (mass produced ) radios used +- 20% components, specialist gear used nearer to the mark components down to 1%, i agree with Rob......regards....Alan.

[glowinganode]

I reckon 20% sounds about right, though depends on the application.
A screen grid feed resistor is a lot less critical than say a cathode bias resistor or a voltage reference chain resistor, although matching to other components values may matter more than actual value.
Rob.

[Geaney]

Thanks folks, I believe I have some resistors that need replacing on the current project!
Cheers, John