Why have capacitors improved so much over the years?

Roger designed circuits requiring perfectly matched output tubes

This may be more marketing than fact. Matching to 5% is really hard and does not last much after the tube is put in service. 10% is considered pretty darned good. Industry standard used to be 20-25%.

@ieales Roger Modjeski moved the standard..see RAM tubes, early computerized curve tracing, many variables tested, etc..

Miss him

you might also be interested in talk he gave at last Burning Amp festival…illuminating

I'm well familiar with Modjeski's brilliance. I'm pretty sure he never claimed perfect matching.

@ieales  My friend has the PSAudio BHK 250 amp and said it sounds best with matched Mullard 6922 tubes.  Perfect matching is rare and maybe Kevin Deal goes for 5% and 10% for his premium and gold matched sets on Upscale Audio.   Maybe I've just chosen 5% and 10% matched 12AX7s, 6922s and other small gain tubes.   Output tubes are the most likely to alter gain and other characteristics during long term use.  That is why manual and/or self biasing is required for output tubes.