If it is an open as Eric suggests that is a pretty short path. Start by clipping one lead of your meter on the center conductor of the right channel input and select it. Set your meter on resistance, if it has a continuity beeper set that on. Set the volume pot at 100%, fully CW.
Now measure resistance to the lug on the input selector switch for this RCA jack. It should be low, like an ohm.
Continue through these points:
The center lug of the selector switch on the right channel
The lug on the pot, an outside lug, that this lug on the selector switch feeds
The center lug on the same deck where it comes out of the pot
Tube pin 3 of the right channel tube
This whole path should be an ohm or two.
Now check the solder joint on right channel tube pin 2 and the solder joint on the center conductor of the right output RCA jack.
That is it!
Somewhere you might lose continuity. Touch up the solder joint where it disappears.
