Thanks for asking.
Believe it or not, I actually designed the Percolator intentionally using these caps…the decision wasn’t all about cutting cost. I could have used a few types of cheaper film caps, but I chose the Panasonic because I like the way they sound in the amp. The cheap 470pF ceramic caps probably seem like an odd decision but I am intrigued by the way they distort…distortion in these types of caps is a function of the voltage across them, they tend to impart more odd order harmonic distortion as the signal through them is bigger. I didn’t have a particular reason (other than cost) for using these particular electrolytic caps.
I fully support and encourage tweaking your amp with different parts. But I wouldn’t change any components until you hear the what the amp sounds like with all the stock components. Then if you do want to change out parts, it will give you a baseline for how the sound has changed.
We get our transformers from a supplier overseas and from a company here in the US called Edcor.
Thanks for the questions. Let me know if I can answer anything else.
Good luck with your build.
-Brach