www.hotrodaudiomods.com/
Bombaywalla...I have the 502A and bought it with the Hot Rod mods. VeraStarr here in Atlanta handled the mods , but I dont know if they still do them, but the link above was obtained via their web site. Mine has the HRAM Street( I think) I know it has the Audio Theta Caps and an ALPS Blue Velvet Volume Pot. Sound is glorious for a minimalist tube amp. I am uncertain of the prices..You may have to call for info. Hope this was a help. I love all your cool systems!
Regards,
Ken