Something unusual I noticed on both my L and R ch. PC-18 boards. The SCA-80 manual (manual links below)states R3=27k

Now look at this photo of both my SCA-80 PC-18 boards. They (R3) are both 330 ohm. I did measure to confirm.
(R3 is between R9=2.2k/1watt and R6=1k 0.5watt; all three are diagonally mounted)

Above: L and R ch PC-18 boars, SCA-80.
https://i.postimg.cc/wMbDP91Z/IMG-1938.jpg

I looked into the R3 anomaly issue a bit. This site features an ST-80 (same as amp section on SCA-80; (manual links below) ...
https://jimkerkhoff.com/2019/03/01/a-dynaco-stereo-80-upgrade/

And the board has the same 330 ohm R3 (the St-80 manual also states R3=27k)

(R3 is between R9=2.2k/1watt and R6=1k 0.5watt; all three are diagonally mounted)
https://i0.wp.com/jimkerkhoff.com/wp-content/uploads/2019/03/Driver-board-with-old-caps.jpg

I investigated more ... maybe the SCA-80Q might resolve the mystery. But no! SCA-80Q schematic only slightly up the value: R3=30k

Note the somewhat similar ST-120 also has R3=30k, per orig .manual schematic (manual links below).

So what's going on?
Note that my SCA-80 was factory wired.

REFS:







Above images are from SCA-80 32-page manual. They pertain to the issue directly. If you want to see the entire SMs, links below.
PDF manuals/schematics:

SCA-80: https://www.updatemydynaco.com/documents/SCA80.pdf

SCA-80Q: https://www.updatemydynaco.com/documents/SCA80Q.pdf

ST-120: https://audiocircuit.dk/downloads/dynaco/Dynaco-S120-pwr-sm.pdf

 

That middle resistor is a 30 kΩ resistor:



Orange-Black-Orange-Gold =30000 Ω, 5% tolerance.

If you are measuring about 330 Ω by putting your probes on that resistor without removing at least one leg from the board, then you are measuring the combined effect of every other component that is reachable in the circuit in addition to that resistor.

 

That middle resistor is a 30 kΩ resistor:

View attachment 368686

Orange-Black-Orange-Gold =30000 Ω, 5% tolerance.

If you are measuring about 330 Ω by putting your probes on that resistor without removing at least one leg from the board, then you are measuring the combined effect of every other component that is reachable in the circuit in addition to that resistor.

You are correct! My bad!
Many issue with other troubleshooting on this unit. Including a another 330 ohm R on the board . Confusing is my duh!

Actually, the value has drifted UP to 32K, after 60 years of moderate use.

BTW:
Do carbon comp R's drift, over time, even if never used? Some YouTuber unboxed a brand new SCA80 kit and had to replace many of the "new"-old CC resistors because of drift.