I am surprised to read your impression of BG caps because they are so far removed from my own. To be clear, there were different BG models and they sound quite different. I find the BG 100uf WKZ (either single or dual 100+100) to be the very best sounding caps for a high-voltage tube-rectified power supply. Bar none. I use the 100uf WKZ caps exclusively in my phono stage, linestage and DAC. In the past, I used them in my SE amps but I prefer these days to run the BG caps more conservatively to give them the longest life possible. So far I have 20+ years on many of my BGs and they are still just fine. BTW, the 50uf WKZ is too thin and lean; it’s the 100uf that has the magic.
There are a number of other BG models that were less expensive such as the VK series, but they sound mediocre at best. The only other BG cap I like is the FK series which came in lower voltage ratings. I find the FK caps just right for cathode bypass duty.
I suspect that it may be circuit dependent as well as interaction with surrounding components.
My preamp is solid state with 30v rails and I have found the large N non-polars (35v and 50v) as well as the NH to sound great.
Funnily enough, the large FKs didn't work in my power amp
Someone mentioned Audio Note Kaisei caps which PQ claims are very close to BG. I wish that were true; unfortunately it’s not. They aren’t even close.
The Kaisei caps are definitely brighter sounding that BGs, but I still like them.
While I am on my soapbox, someone also mentioned Audio Note niobium resistors and all the research work that went into developing them. I have tried Peter’s niobium resistors, regular and silver, in a number of places, and to my ears they are too colored—much too lean in the bass and too bright as well. The best sounding resistor Audio Note makes is the 2 watt Silver Tantalum. (Not the 1/2 watt or 1 watt, and most certainly not the regular non-magnetic tantalums.). I use many of the 2w Silver Tantalum’s throughout my system.
Interesting that you found this. I have some 100KOhm in both the 2W silver tants and silver niobiiums to try in my stepped attenuator. I have always found tants to sound a little dark compared with carbon films. I have no idea about niobium.