Re: What's your best guess...
The best of luck to you.I started out repairing the old tube stuff as that was the current technology as I was studying electronics with CIE.
I still have lots of tube test equipment,scopes etc.
Ebay is the place for tubes these days,I have quite an inventory of odd voltage (TV) tubes that I will never use.

Don't fall for the brand name trap such as the Fender price for a 6L6 is $65.00 each the last that I knew,I bought a matched pair for $28.00 on ebay that tested and worked just fine.Their 12ax7 is $25.00 or so......waaaaaay over priced.
I would like to try to make a printed circuit board someday,you can buy the kits and there are places that will design the printed circuit silkscreen for you for free.I bet that there are computer programs for free that will do it for you.
Google "Spice Electronic Software free" and look at the hits,it is a great resource for experimentors.I used it back in the DOS days,what a blast to be able to predict how a circuit would work.
In any case,good luck and if I can help or confuse you let me know.Ron G