My CTC-16XL Project.

[old_tv_nut]

Looking at the photo of the color board, it appears the original resistors were carbon composition. I think these could change value by a couple of percent due to heat of soldering, subsequent moisture absorption, etc. even if initially matched. However, it's hard to guess what they had in mind since they don't tell you.

If you just throw in 5% tolerance resistors, the center voltage could vary by as much as +/- 1 volt (because there is 40 volts across them), so that must be too much, since unmatched resistors are not allowed here. 1% resistors would cut this down to +/- 0.2 volts, which certainly must be close enough, since this is about the closest tolerance you could achieve with an analog ohmmeter anyway. Since carbon comp resistors probably would not hold such a tight tolerance, my guess is that somewhere in between, like a 2% match, is OK.

If this were a professional monitor circuit, it likely would have a pot between the two fixed resistors, with a procedure for zeroing the output voltage under certain test conditions.