Fur - Two observations:
1. The sign wave signal appearing at the top of the volume control in the first pic looks very compromised, with the bottom crest of each wave looking very bloated, while the tops appear rather normal. I would connect your scope directly to the source you are using to verify if this is a source problem, or an additional problem in the Fisher.
2. The signal at the output terminals from both channels appears to be compromised. Granted, the right more than the left, but both compromised above and beyond the potential source issue noted above. With both channels showing the same issues then, that usually speaks of power supply problems, since that is the only thing in common with both channels, other than the source. Either that, or the same mistake has been made in both channels.
3. With no signal applied, do the outputs show a flat line? Or is there garbage present with no signal? Advance your scope sensitivity to check.
4. Have you verified that your OPTs are the later version units?.
5. Remember that with the modified amplifier, the NFB is taken from the 4Ω tap -- NOT the 16Ω tap as was done with the original design. Make sure you moved the NFB lead from the 16Ω tap to the 4Ω tap. Failure to do this will result in twice the amount of NFB applied to the amplifier, and unstable operation as well.
Let us know!
Dave