I cannot offer gratis technical support at this time. For other inquiries you can reach me at Chris at PreservationSound dot com.
If you have some old audio item and want to know ‘what is it worth?,’ your best bet is to examine the ‘sold listings’ on eBay for similar items. That’s where I start,,,
If you want advice about how to do develop the skills necessary to scratch-build and repair tube-type audio equipment, I can’t offer any to you. There are a great many people for whom this is just not-for. It’s a frustrating, difficult, dangerous, and fairly expensive endeavor to train one’s self in. On the other hand, you might take two years to get-to where I’ve gotten in over a decade. I just don’t know, so I am not going to offer any advice on this subject.
That being said, I can share with you how I developed the skills that I have. I was in a rock band that toured a lot. We used big vintage Fender tube amps. They would sometimes need servicing, and at the time (circa 2003) the tube amp repairmen we could find in NYC were expensive and/or unpleasant and/or incompetent. We had a few bad experiences, so one day in Nashville I picked up an on-sale copy of Aspen Pittman’s “The Tube Amp Book” at Valley Arts for $15. I figured it was worth a shot seeing if I could fix my own gear. I read the book over and over again that tour. When we got back, I bought a basket-case Tweed Gibson 50 watt amp on eBay for $120. I had basic soldering skills (I had built a few science fair things and a PAIA theremin kit as a kid) but that was it. I read a few blogs and it seemed like the Fender 5F2A Princeton was a useful amp that was a good ‘beginners’ project. So I decided to use the chassis and as many other parts as I could salvage from the Gibson and make a 5F2A clone. It took about a month, and it worked but it sounded fkkn awful. So I did it again, this time with a fresh Hammond aluminum box. This one took about A YEAR. It had a parasitic oscillation problem that literally took a year to figure out. But once I squared it, it sounded pretty good! So I built another one. And another. Now it was getting easier.
I moved on mic preamps. I started with the RCA BA2C because it seemed simple. I think I got lucky and I figured that out pretty quickly. So then I started trying anything I could – Tremoluxes, phono pres, power amps, more mic pres, compressors, ETC, ETC, basically whatever I could make that did not require fancy custom-would transformers or inductors. There were many successes and some very frustrating failures. And all along, as I was making all this stuff (probably around 200 scratch-built pieces at this point), I was buying any and every cheap (under $30) old tube amp I could find and either fixing it up or parting it out if it was too effed. Once I fought my way through a few hundred old chassis of every stripe, I had been exposed to pretty much every layout, wiring, mechanical, and related non-schematic quirk that actual trained designers used in the original tube audio era.
I bought decent tools, I use a temp-controlled Weller soldering iron, I have basic multimeters and a $300 scope and some decent basic audio test gear. I use a solder-fume extractor and safety glasses whenever I work. I buy most parts from Mouser, Antique Electronic Supply, EDCOR, and Jensen, and most tools from MCM electronics. I try not to read too much commentary online because the internet is simply not a reliable source of information; instead I bought hundreds, maybe thousands of old issues of Television and Radio Repair, AUDIO magazine, the AES Journal, etc., etc. Primary-source documents, essentially. The internet is, however, useful as a source of schematics, and I have downloaded and/or screen-captured just about every single tube-amp schematic I have ever seen – many thousands – I and I keep them all indexed on my macbook and always take the time to study every one of them looking for new (old) ways to do things. I don’t fully understand all of them yet, but maybe I’ll get there someday.
Thanks and have a great day.