Why have capacitors improved so much over the years?

Engineers who designed professional gear 40 and 50 years ago cared. Back then I knew some then 'old timers' who were aware. Can't comment on earlier, but no doubt some were aware.

I had a tube 'guru' tweak my Citation II with better resistors, caps & wire. Same cct & old tubes, but OMG.

jfd11, hmmm, you have to tell us the name or it's like it never happened. 

Redwood, I bought most of mine from Surplus Sales of Nebraska, when I didn't make my own.

At the Surplus Sales website, click on 'capacitors' in the left column, then on 'air gap variable', then go to the 'quad' section. There are some with 4 sections, each of which maxes at 460pf, for about 1.9nF or 0.0019 uF when paralleled. With judicious design, one can create an RIAA network with values in that range.

Warning: they're big and expensive. But it's the best sound available.

@ieales - thanks for the link, cool history.

@terry9 thats a wild website… I have no idea what I’m even looking at with those air caps!

My visitor was Ken Stevens of  Convergent Audio Technology. His wife, I believe was from the WNY area.