Scratchy sound is often just dirt. Use DeoxIT D5 [16] for metal switches and DeoxIT F5 (FaderLube) [16] for carbon-track volume and tone knobs.
When servicing output transistors, always clean the old, dried-out grease and apply new thermal compound [15] to ensure proper cooling. Where to Find Schematics & Lists sansui amp parts
This community is the best place to find verified substitution lists [9] for discontinued Japanese semiconductors. Scratchy sound is often just dirt