As with all vintage electronic equipment, the capacitors are most likely bad and require replacement. This equipment will be no different, with a number of paper, plastic, film, and electrolytic caps in each component.
Since I have a factory schematic for the Power Amp, all of those caps have been cataloged and some replacements have even been ordered.
On to the Preamp
From those initial pictures and the live view, some kind of mold had been growing on the front panels. After removing the electronics from its wood enclosure, I figured out how to separate the front panel from the chassis by removing the knobs and the chassis screws.
Similar to the power amp, the internal electronics is in fairly good condition since the housing was sealed tightly. Below is the top view. Notice the dust on the 3 tubes on the left (these are exposed in the rear of the unit).
Bottom view shows more of the wiring.
Next is the front view exposing the control shafts. On the bottom left is one of those capacitors that needs to go. Check out that rectifier (in blue): that is a classic!
Finally, the rear view showing the input/output connectors and the 3 tubes.
Notice the plastic container holding up the preamp...this is where I put the filthy knobs. After a failed attempt at trying to remove the white mold-like "substance" from the knobs with water and a toothbrush, I determined that a good soaking or more industrial cleaning would be needed.
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With no wiring diagram to follow, it will take some time to "Reverse engineer" the wiring and put it into a schematic. This is something I did often back in the olden days when I was a Ham Radio guy and was always trying to understand circuits from existing equipment. Don't worry, once complete, I will post it here so you can build your own!!
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