Tekton Double Impacts

Would you guys quit talking over my head? :) While I don't know the differences in the different types of caps you're talking about it sure makes for interesting reading and I'm learning more all the time. 

Aric, I keep forgetting that you're a speaker designer with all we've done together involving amps and preamps. Since I love the look of the giant Duelund caps so much I think I'll make some faux ones to put on my crossover board and use less expensive caps that are actually wired to the speakers....or better yet I'll make my external crossover box look like a huge Duelund cap!

Aric, would you make an amp based on the GM70 tube? I would love to try one.

@charles1dad  Those are good questions! For a cost no object, I would likely go the exclusive film cap route in the power supply- since even the best 'lytics will tend to drift with age (however good quality modern caps last MUCH longer than those of the 70's and 80's). What I like to do in most cases, is use electrolytics bypassed with small film in the first stages where massive filtering is required, and then have the last stage be pure film since it's the last part of the filter before the audio stages. 

As far as coupling? That's another tough one. Inter-stage trafos are technically superior in the phase region (where multiple stages are required), and also when you need a step up or impedance matching transformer. However iron has it's drawbacks in terms of frequency extreme rolloffs, so you trade "possible" phase issues for "possible" response issues. However in practice using good quality parts- these issues are small and splitting hairs so long as the design is done right. 

I for one think that high quality caps can get a design that sounds phenomenal so I typically don't look into the interstage transformers much. However, on a tube that requires a huge voltage swing and lots of low current to drive it (ex: 845, 805, GM70), it's almost necessary to use an interstage trafo as there's so much in the signal path otherwise. 

@333jeffery - Someday perhaps! I think my first 1kV triode will likely be the 805 or 845, as I've got the basics on a design down for those. The GM70 is very similar, but in all cases these designs are not cheap to do right. Using over 1,000 volts and requiring 2-3 stages to drive these huge tubes is a very deliberate complexity. The 300B, and 2A3 are next in line as far as needing low current, high voltage swings. The easiest tubes to drive are the Pentodes or Kinkless Triodes (KT88, KT120, KT150). The general rule is the less stages in the signal path- the easier it is to make an amp that sounds transparent in my opinion. 

Drat! Too late to edit. That should’ve been "as far as needing high current (low impedance), high voltage swings".