Brian, the amp looks in great shape!
Still, one thing about electronic parts. They can look just fine on the outside but be totally snackered internally! Like most things in life, good looks is no guarantee of good performance.:smile:
Since the amp sounds ok but just a bit ratty at high volumes there could be a few things that could stand some attention.
The speakers may be old and the cones breaking down. Or the cab may be coming a bit loose in the glue joints and you're getting some vibration from the wood. Try an extension cab and that will confirm it one way or another.
The electrolytics (dual units, brown guys with 2 wires at one end and one wire at the ground end) appear to be original. That means the power supply electrolytics that are under the "dog house" metal cover on the top of the chassis are probably original too. These dry up internally over the years and stop doing their job, which in the power supply is to filter out all the power supply hum and in the preamp circuits along the eyelet board they put big gobs of gain in each 12AX7 stage.
Even if you aren't hearing much power supply hum old filter electrolytics can cause weird noises and ghost notes. The smaller ones in the preamp will drop the gain a whole bunch! Yet these caps may look pristine from the outside.
Electrolytics have a wet paste inside which slowly dries up even if the amp is never used. Heat speeds up the process but even in storage it still will continue. Normal expected life for these caps is 10-20 years. How lucky do you feel?
Those big blue couplers are kinda chintzy, too. Fender was saving money. I'd rip 'em out and put in Orange Drops myself. That's just my personal taste.
The nice thing is that it appears no one has dinked around with the wiring! Makes things so much easier for a good tech to work on.
Anyhow, that's about all I can say. I suspect the old caps may be causing the "rattyness". A complete cap job on an amp of this age is always a good idea, period. If the rattyness then disappears then great! You still won't be sorry!
Who knows what the bias setting is, either. Old tubes may be the problem.
All in all though, a great score!
:food-smiley-004: