I'm the proud owner of a reviled Burton 8x4 (heh-heh, just kidding) and I'm having a blast with it.  Assuming there are no failed glue joints and the instrument is solid, the biggest issue for a Burton would be the jacks because, as you know, the replaceable tongue/plectra units are no longer available. I think it was Glenn Giuttari (harpsichord.com) who discovered you can replace the Burton tongues with Hubbard tongues and Delrin plectra. When I got my Burton, I immediately ordered tongues, plectra and damper felt from Hubbard Harpsichords. When I was placing the order with Hubbard on the phone I got the impression they would be willing to do the jack conversions for you, but you would still have to do the voicing yourself.

To prepare the jack you remove the Burton tongue and then enlarge the tongue "axle" holes with a small drill.  I think it's a No. 52 drill.  I used a pin vise to hold and turn the drill. It's like an Exacto knife handle with three or four jaws instead of two. I tried a cordless drill but it was too unwieldy.

The drill was actually a little too small so I had to spend some extra time using a 7/64 allen wrench/hex driver to burnish the holes a little larger so the tongues could move freely. Perhaps the next larger size drill would work better.

You also have to slightly shorten the angled end of the tongue.  I made a cutting guide from a 2x3 with a 45 degree angle cut on one end to guide a sharp chisel. The tongue fit into small slots in the bottom of the guide such that about 1/8" projected out to be sliced off. Popping the Hubbard tongues into the newly enlarged holes is tricky.  I had to clamp a screwdriver vertically into a vise and insert the tip of the screwdriver into the tongue recess in order to consistently "spring" the jack open far enough to pop the new tongues in.

Voicing took a long time because I had never done it before. Those plectra are so tiny that I had to buy a head magnifier. I worked a little each day and finally got all the 8' jacks done with close to a 70 gram touch throughout. I had better luck with the Exacto titanium blades than with the standard blades. And I spent a lot of time scouring the internet for instructions and hints on voicing plectra. 

You have to be careful when adjusting the bottom jack adjustment screws because it's easy to crack the jack base.  I don't think those bottom screw holes are factory threaded and while the screw is cutting its own thread it stresses the plastic. I bought an appropriate tap to improve the threads. But you have to be careful there, too, because it's easy to make the hole too loose.

I think I'm the fourth owner of this Burton. The instrument it was never completely finished and the last owner didn't do much more than painting.  It was very hard to play because of the worn tongues/plectra which the previous owner had adjusted for touch using the tongue screws (a no-no).  The Hubbard tongues and plectra took care of that problem. It took a long time to do the conversion but I wasn't in a hurry.  I also had to level the keys and rebush a few loose or noisy keys, as well.  It was a great learning experience and an experience I wouldn't have had if I had bought a $10000 instrument that I was afraid to touch. 

Now for the disclaimer: my Burton is currently working only with the 8' jacks. Although I have all of them, as far as I know the 4' jacks have never been installed to work properly. Somewhere along the line it seems the parts for the slide/stop levers were lost and some builder installed a cobbled up homemade arrangement. The 4' lever is attached to the 4' slide off center so that the slide is slightly twisted at the treble end causing the jacks to jam in the slots. This is fixable but I haven't had time to mess with it. However, it's great fun playing with only the 8' strings and everything sounds fine to me.  After all, no two harpsichords sound the same anyway. I just pretend it's a spinet :-) And, by the way, except for touching up a few high treble strings occasionally, it holds its tuning very well through most of the year.

I scanned the entire assembly manual (with the permission of the manual author, Charles Burton) for the 840 Hubbard and the pdf is available here :

https://dl.dropboxusercontent.com/u/55530059/Burton_840_Harpsichord_Assembly_Manual.pdf

I have also been given a Burton 848 assembly manual but I haven't scanned it yet.

If you decide to purchase the Burton I will be happy to help you get it working. Just contact me offline.

Bill

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