Huh? The ST-70 was originally sold as a kit, to be assembled at home, by beginners.. I've owned one before and seriously there's nothing complex or special about it in terms of making it work, especially for a tech with any experience working on tube amps.
A basic rebuild in my opinion consists of changing the electrolytic and paper capacitors, changing the selenium rectifier to a 1N4007, measuring the resistors for tolerance, test the tubes and replace if required... test amp for power output and distortion, then let it play for a day or two to be sure nothing else is wrong. Simple as that...
All the parts can be easily bought, and the net is overflowing with info on this amplifier. I think the issue here is how someone runs a small business though, not how to rebuild a dynaco.
When this thread started I thought this was about an Eico ST-70..........now after reading the rest of it, it's a Dynaco ST-70? Well....both were designed as kits, and as a few others have said previously, they were simple amps made in a simple time and their really is nothing to restoring one of these yourself if you know how to solder. Parts availability is not a problem, probably one of the best vintage amps to own in that respect.
If it were me I would call them and express the fact that even though they had "extenuating circumstances" that that was their problem and should not have been made yours without any kind of notice. I agree with others......don't let them do anything more to it, if they've even done a thing to it, and have them send it back to you at THEIR expense. Simplicity or not, a rush job is a rush job. Things can be overlooked by just trying to push it out the door, even if you are the greatest tech in the entire universe.
I agree that the issue is how the small business is run. Anybody in this day & age can have a slick looking website with a fancy looking email address attached to it. They may do quality work too, but it doesn't help the customers or the business owner if that's how they run their business. These people obviously knew that they would be moving soon, and trying to operate a small business while doing that move is near impossible for anyone, especially when the home & business are located at one in the same. Clearly, ALL of this guy's customers that had equipment in should have been notified this from the get go, that way they wold know that there would be a big delay. It's easy to gather all those email addresses and send a mass email.....clearly they couldn't be bothered.
If I were the OP, I would get the amp back as-is ASAP. Then I would do the work myself.
This is why I don't trust anybody but myself to work on my equipment, and I'm not a tech! If I make a mistake, then so be it. I can always admit defeat and get some knowledgeable help later and get it working again. Six months for a non-repair from a supposed professional is not acceptable in my book, especially since it has been way out of the original promised time frame. You could have purchased a dozen of these amp and fixed them yourself in that time frame! The Californian's ethic of "Dude, I flaked!" is not an acceptable response in my book, yet people let them continue to get away with it.