Vintage Tube Amplifiers - Any good?

Some consoles were pretty good. Many were terrible!
But there are plenty of vintage amps that sound great on modern speakers:Harmon Kardon Citation 2, Dynaco St-70, Marantz model 8 and model 9, Fisher, HH Scott and so on. Any of them would need the power supplies rebuilt at the very least in order to be reliable.
Some console amps weren't too bad but they also would need to be rebuilt. Generally speaking the drivers in many consoles were not very wide bandwidth and didn't handle a lot of power. 

We played around with old gear like this back in the late 70's. Vintage speakers connected to modern stereo, modern speakers connected to vintage amps, that kind of thing. I had built a Dynaco Stereo 400 but didn't really know anything about how to modify circuits or even swap out parts like caps to improve the sound.

Based on what I know now here's what I would do if I had a vintage console: as little as possible. Most of these things are pretty simple. Great big solid wood box with simple circuits with point to point soldered wiring in an open sheet metal chassis is pretty common. The speaker(s) are always paper cone stamped frame cheap looking things which nevertheless if you hook them up to something modern you will be surprised how good they sound. I would take them out but unless damaged would put them right back in. 

With everything out I would carefully refinish the cabinet. Use Fine Woodworking or other trusted source for what to use and how to do that. Huge amount of the charm is in the appearance. When in doubt just clean it up, give it an oil rub, call it good. But there are woodworking techniques for restoring or recreating original finish. This is at least as important as anything you do electrically.

Most of these things have the sound coming from a solid wood opening with fancy patterning with fabric with more fancy patterning behind it. Cleaning that fabric or finding authentic replacement could be one of the trickier parts of the whole thing.

Then simply go through the electrics and clean, test or simply replace tubes. Might redo solder but I wouldn't re-wire, at least not unless you can source original looking wire. Half the cool factor is the old school look!

Then I would put it all back together with one modification, either new quick-release fasteners or and open back. You want to be able to see and show off all your great work.

On the same page re:the cabinet.  Some are very nice pieces of furniture and with the proper restoration can look great.

Before (phono/FM tuner) and after (speakers) the amp - no comparison to modern tech with you hitting on one of the big ones which is the material used in the cones.

My thoughts on the amp - outside of class D, amplification hasn't changed much over the decades. Heavy transformers, big capacitors, no thoughts whatsoever about efficiency ... are all hallmarks of a simple linear, expensive and hopefully good sounding amplifier.  Assuming it was a quaility console to begin with, the parts used were in wide ciculation and of notable performance given that over time, component tolerances would vary significantly but the units kept on working.

Everyone needs a project - I guess this will be mine for a couple of months! :-)

I love the old tube console stereos. I have repaired some of them and left them as-is, and some of them were too bad so I removed the amps and junked the console. One comment I would have based on my experience with the Zenith, Magnavox etc. is the amplifiers in them are low power and noisy (poor signal-to-noise ratio with lots of hum and static). The low power limits them to be used in high sensitivity speakers, which unfortunately just reveal how noisy they are. Also I have been told that the output transformers are limited in their bandwidth purposely to cut out the low-end frequencies so the console doesn't thump. I found it was better to just enjoy the consoles as-is because installing the amplification on modern speakers just exposed their faults and deficiencies. As someone else stated, you are better off with High-Fi tube amps from back in the day (Dynaco, Harmon Kardon, etc.). Just my opinion thanks and good luck.