How far have ss amps really come in the last twenty years?

Seems that some of the classic designs have stood up relatively well...I have not been motivated to explore potential alternatives to my Threshold SA/1 monos 

After a lifetime of success in modifying components with spectacular results, I’m going to share with you my latest endeavor, which is still in progress, but so far has been a series of errors.

To begin with, I didn’t make proper evaluation of the job. In the past, I used expensive parts to improve not so expensive amps or preamps; the "mono blocks" I’m upgrading now are not inexpensive, they’re PrimaLuna. Next I didn’t make a proper evaluation of space needed for the new parts; I simply projected this grand vision in my head as to how much better these mono blocks would sound after these improvements.

"Mono blocks" require twice as many parts as a single amp; "no crap"?. Acquiring these expensive parts was a problem because no one had the number of parts needed, which meant I had to go to more than one vendor, that took awhile. After I acquired them, I realized they’re larger than parts presently in the amps.

I’ve had this pile of expensive parts for a year now, and I have yet to pick up a screwdriver or a soldering iron. Let me explain: These parts are "much larger" than the present parts in the unit; that means I’ll have to modify the case.

These units have 8 tubes per side; the tubes have to be removed, and the unit turned upside down before taking the bottom off and investigating.

A prizefighter doesn’t just get in the ring and say bring it on, he must be mentally prepared; I have to be mentally ready for this fight, and so far that hasn’t occurred.

My quandary: while I’m certain these parts will bring about that glorious sound which I seek, these Primaluna mono blocks that I’m enjoying, are not exactly mediocre in they’re present state.

Since I’ve shared all of my past successes in modification of amps, pre-amps, and other components, I thought I would share one that is still in progress.

"But is a modern resistor or capacitor really better sounding than what they used 50 years ago? Are modern amplifier circuits significantly different from the classic ones? To a basic amplifier circuit, all you can add is complexity, and that, in my opinion, is not necessarily a good thing."

Without a doubt; resistors, diodes and capacitors have improved in the last 50 years. Utilizing new parts will make a night and day difference with the same design.

@jdl57  If your Sound Labs have the original toroid backpanel, there's a tweak you can do that makes the speakers a lot easier (and better sounding) to drive! Alternatively you could get the new "Toroidal 2" backpanel that pretty much does the same thing.  If you really want to hear what ESLs do, traditionally since the Quads first appeared, ESLs and OTLs have been the way to do it. If your Sound Labs are so old that they have the original EI transformers for the high frequencies then they are already easy to drive, unless the bias controls are damaged which is very common with the older Sound Labs.

Hi,
sure ss amps have evolved mainly in efficiency, transparency, having better parts and construction (new materials). Design philosophy basically the same, music presentation different.
A 20 year old top amp then will still sound top today.