Resistor tolerances

[N9axl]

I am working on this Johnson Viking 2 CDC.  I see the majority of the resistors are 5% tolerance.  Most appear to test within tolerance, but a very few are at 10% or 20%. Does this really matter in terms of function or replacement?

If I have a 10% replacement resistor in my box is it worth it to order a 5% resistor? Should I just leave the ones out of spec up to 20% installed unless I see a problem ?

What I'm wondering is whether these are at 5% for some functional reason or simply because this was built for government use so they simply used higher quality parts?

[KA2DZT]

5% resistors come in a greater range of values.  So, some values only come in 5%.  Measure the resistors that you have and if they are close to the value needed, use them.  5% resistors that are 20% out of value probably should be replaced.

Fred

[WA2SQQ]

Back in the late 70's when I was with Panasonic's component division, carbon comp resistors were the prevalent variety.We had a strict 2 year shelf life because their value would change over time, often the result of moisture absorption. If the components were installed, and in use there wasn't any problem. Sometimes, after a few hours of use any internal heating that might occur will dry them out and the value can change to be back in tolerance. Carbon film resistors are less susceptible to moisture variations. I'd run the radio for several hours and start checking. If you find any that are more than 10% off, replace them. Easy enough and cheap enough.

[WD8BIL]

Change the ones in the bias resistor ladder to provide the voltages needed. I've found on my Vikings 1 and 2 that the listed resistor values may not provide the correct voltages given the line voltage differences.

[KB2WIG]

And while yer in there, check the meter shunts with a gud quality meter. You can buy replacement  shunts from Mouser.


klc

[N9axl]

Thanks. I think the idea of letting this run for a few hours and see what the values are is a good one.  This has been stored in a dry place since I see no rust but I suspect it hasn't been turned on since probably the late 60s -- so I'm sure there's some moisture in the resistors. Am waiting on some electrolytic capacitors and some tubes but this seems to be going along good so far.