Hi Jim,
In selecting a jack, the first consideration is fitting them to the guiderails, upper and lower. Most shapes and sizes are pretty close to one another with respect to the top guides, but it doesn't take much variance for a jack to be too sloppy in the guides, or to be tight enough to bind. Bottom guides might be rectangular, or they might be round. Placement of the round ones might be centered on the jack or set in line with its edge (Hubbard). So that is generally the top consideration in selecting a replacement jack, as replacement of the guides (especially the lower) is fairly involved, time consuming, and expensive.
I definitely prefer a simple jack that is somewhat like the Hubbard model: rectangular in cross section, a slot for damper felt, a tongue that pivots on an axle, a slot for delrin plectra with a cross slot for easy removal of broken plectra.
Tongues that pivot on axles come in three main designs. The most common historically would use a metal pivot pin somewhat like a center pin in a piano action. Those are often hard to remove when a tongue needs to be replaced, because often the hole is drilled through only one side, with the point of the pin burying in material on the other side. That design is common with wooden jacks, and works very well (and tongues in wooden jacks will rarely need to be replaced). Wooden jacks typically use boar bristle springs, which are nice in that you can easily control how strong they are, but a little tricky to install and replace. I've seen plastic jacks with metal axles, but don't know of any that are commercially available (possible Hugh Craig?)
You are more likely to be looking for plastic jacks. One of the other two main designs with axled tongues is the Hubbard, with slots in the jack body into which the plastic axles of the tongue slide, and they are held there by the pressure of the spring, working against the top adjustment screw. It is a good, workable design that is pretty convenient to service. The adjustment screw is screwed out, allowing the tongue to pivot forward and the axles to slide easily out of the slots.
And the other is the snap in, where the plastic axle pins of the tongue snap into holes in the jack body. This is common to a number of jacks, including Kingston's, the old Burtons. The snapping process is a little tricky, but you get used to it. One drawback there is that if you use too thick a damper felt in the slots of those jacks, it will tend to cause the body of the jack to bend inwards, binding the tongue. That is, the slot is pressed outward, and as a result, the plastic that extends below the slot is caused to press inward. This can lead to sluggishness. However, as long as you are careful to use damper felt that is not over thick, it won't be a problem.
Lutz' from Instrument Workshop are an interesting variant, with the "axles" being nubs in the body of the jack, onto which the tongue snaps.
Top and bottom adjustment screws are somewhat a matter of taste. I like to have them, especially the bottom screw, as it allows for refinement of staggering. Every time you re-quill, you might change slightly the amount of key dip needed to take a jack all through pluck, and this will affect the stagger. Also, humidity change will affect string height, which will affect how far the plectra are beneath the strings. Having screws to raise or lower all the jacks a bit is a big improvement over having to file the bottoms or add material. The top adjustment screw can be very helpful from time to time, but it is less necessary.
The Zuckermann jack does not have a tongue pivoting on an axle. Instead, it bends back and forth on a spring (which is part of the body of the tongue). I don't like them, nor does my wife who is an accomplished harpsichordist. Lots of people seem to think they are fine, though.
Top two: Hubbard and Instrument Workshop (hubharp.com and fortepiano.com). But fitting the rails may make those two unusable for the given instrument. Next on my list would be pearwood jacks, available from a few sources. More expensive, and they take a bit longer to get set up, but they function beautifully if well done.
There may well be other jacks available of which I am unaware, probably from outside the US. I'll attach a photo I took of a variety of jacks: Hubbard, Zuckermann, Instrument Workshop, Burton, Bolton (no longer available I think), OLD Zuckermann (60s) and wooden.
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Fred Sturm
University of New Mexico
fssturm@unm.edu http://fredsturm.net "The true sign of intelligence is not knowledge, but imagination." - Einstein
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Original Message:
Sent: 07-09-2012 13:06
From: James Busby
Subject: Top jack choices
All,
I need to replace all the jacks in a harpsichord for a friend. (Long story) Ed talked about a generic jack from England, and there was talk of other jacks, but would some of you mind listing your "Top Two" jacks and where to get them? I guess the question really is this; Which jack do you think is the "ideal" jack, and why??
Currently I have 8 (!!!!) harpsichords I work on, and each one has different jacks. I prefer the screw on top and the capstan on the bottom for ease of regulation, but I'm open to education. While the Willard Martin lacks the top screw and another lacks any adjustment on the bottom. Most have both. Fred mentioned the "sponginess" in some jacks of this kind. Any help would be appreciated.
Thanks!
Jim
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James Busby
Mt Pleasant UT
801-422-3400
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