Every country has some brilliant designers in varies areas .
Each designer may just have a different design layout
all depending on what characteristics you are looking for .
many old Western electric ,and RCA Williamson tube layouts
were just improved upon as technologies evolved such as capacitors especially polycaps, and better tighter transformer windings ,and mosfets, bipolors, transistors and power supplies.Even today many. $5-10k amplifiers use average parts ,for only 20% of the build on average actually goes into the parts ,the rest casework overhead
and markup. Meaning you can get a Lot more potential out of
most equipment if you have the $$ to upgrade or mod it .
i have been doing this with especially Loudspeakers ,
and electronics for years .modern technology if high quality
over $10k has much better quality parts such as Gryphon ,BurmeisterMBL I sold Audio in the UK , Smaller highend companies in Europe on average use better quality parts on average per $$ dollar spent then in the US , especially the Danish companies.
upper Pass Labs, Boulder , EsotericAccuphase,Goldman Shindo
just to name a few allexcellent products , depending on budget.
rebuilding a solid classic - dependable piece of equipment does make a lot of sence look at Modwright as a excellent example
take a solid piece of equipment and stuff it with top quality parts
a Huge payout in sound . I sold upgraded equipment for years .
if you plan on keeping it it makes sense on upgrades. If you like to change equipment every few years don’t bother . When selling used most people don’t know ,and can’t appreciate the better quality parts on paper ,and will not pay the extra freight.