Recently acquired a really cool c.1960 Gibson GA-40 "Les Paul" amp. It uses 5879 preamp tubes, and has a ton of zing. My tech had a converter to run an EF86, and that sounded much sweeter and fuller than the 5879 in that application. I can't find a similar converter online to save my life. I've found one for putting a 5879 into an EF86 socket, but not the other way around. My tech got his a long time ago from a Chinese supplier on eBay, so he wasn't able to point me to a direct source. Any ideas? thx!