I don't have the time to watch the whole of the videos. Skimmed the first two so far. In a former life I manufactured parts for amplifiers, including whole reproduction fender amplifiers, particularly Deluxe Reverbs. Mojo used to sell our chassis until they got in the fabrication business themselves. Also we used to wind our own transformers in house as well. I also did restoration repairs as well. What you found was a common 1 hour recap job. Its what most shops do. Nothing against it, but it is typically a lets do this fast and get the customer out of here type thing, and you have problems like you found with the socket pin filling with solder and not allowing the tube to seat properly and such. Very common. You should actually solder the socket with a tube in it. Does not need to be the actual tube and can be a sacrificial bad one. It keeps the heat out of the lower contact and the solder will not flow all the way down unless you are just using way too much heat and solder and you actually flow the tube pin!. That is just shitty workmanship. When it comes to drifting resistor values, it is very possible they were out of spec before the amp was even built. Fender was notorious for getting surplus old and out of spec resistors. It was not until Ed Jhans took over that they had a real quality control system, but here is where the rub is. Later amps were said to not have that little special touch. As engineers we call "Special touch" out of spec O0 but beauty is in the ear of the beholder. I personally like my amps running at peak performance. I have yet to watch the third video but am assuming biasing will be addressed. It is a little tricky with these amps because they place such a high plate voltage on poor little 6v6's and they were designes to take advantage of the super tweaked and nuanced mass produced 6V6's from Sylvania, GE, and RCA of the mid 60's which were really well made tubes. They modern Electro Harmonix 6v6EH from the reflector plant is actually a reasonably good tube and matches up well in that circuit. The recommended biasing procedure in those days was to apply a sinewave. Typically of the lowest frequency of the -1DB point of the output transformer as full power. I believe its about 100hz for a deluxe reverb. Perhaps a tad higher. Adjust for rated power output and no crossover distortion. return to no signal and make sure the tubes are not dissipating too much power at idle, then take the amp into clipping. Adjust bias up to clean up the square wave a little and check for anodes to not be beginning to glow. Return to clean rated power and observe maximum dissipation and again check for no anode glow. Return to idle and check for dissipation. It was not a really exact science. What sounded good at clean rated output may sound terrible under heavy clipping. That's why they had to be run a little hotter and the transformer impedance was played with to get them in a reasonable spot on the transfer curve of the tube at that point where the distortion was not cold or harsh and the tube was not melting.
That's enough out of me! Now off with my head!
Please have a look at a article I wrote a little while back as you may enjoy it.
http://hackaday.com/2016/03/24/flying-close-to-the-flame-designing-past-specified-limits/
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