Bob Humes' articles posted in the "tech" section of the MMD archives
forms a comprehensive treatise on making Wurlitzer valve blocks (unit
blocks) and really can't be improved on.  But here are a couple of
additional observations.

The examples recently offered for sale on eBay seem to have stirred
up a controversy over a few issues.  The most important one is the
direction the metal valve cover should face.  Bob Humes' illustrations
show the only correct way: the sharp inner edge of the opening should
face "up," so that it is away from the leather poppet facing.  To
seat tightly in both open and closed position, a poppet needs a certain
amount of wiggle room, and having that sharp edge facing down defeats
this purpose.

Second in importance is to construct the poppet as Bob shows, not as
Player Piano Company (PPCo) unit blocks are made.  The throw of the
poppet needs to be adjustable, meaning that it must consist of two
separate leather-faced discs on a threaded stem.  This complicates
the poppet construction a bit, and Don Teach's contribution cited by
Robbie shows how to use a Pem fastener to make the threaded stem.
Bob mentions the .035" throw of the poppet, and shows a device for
accurately setting the throw.  PPCo recommends using a fabric disc of
appropriate thickness for setting throw and fishing it out afterwards;
but that might not work well with the threaded stem in the way.

Actually, with a little experience and the use of the mouth to provide
vacuum to operate a valve block, you can tell by the feel and sound of
the block, as you open and close the nipple with your finger, whether
you have the right degree of poppet travel.  There should be a nice
clean snap to its operation, with no sound of wasted vacuum.  According
to expert Durward Center, an organ with a dual-tracker system is more
demanding in its requirements with regard to poppet travel than a
single-tracker organ is.

Other variations shown on the eBay postings are the material used to
seal the valve cap and the direction in which the nipple points.
Wurlitzer used burnt shellac for sealing metal to wood, and that is
what should be used here.  PPCo washes its valve blocks in a gummy
sealer (Phenoseal?) and uses that same stuff to seal the valve caps.
It is rather nasty and unattractive stuff compared to the shellac Bob
Humes recommends.  Certain eBay blocks show the nipple elbow pointing
down; I don't know the reason for that, since as used in the organs
I have seen the nipples need to point upwards.

Incidentally, original Wurlitzer valve caps were made of a soft
metal, and are not worth trying to save and reuse, when rebuilding
valve blocks.  You are likely to distort the seating ring of the cap.
So it is safer to pop them out and use the stainless steel caps sold
by PPCo (cat. no. 706; $1.32 ea.) to replace them.  Those PPCo caps
can be reused, if you are around for a second rebuild.

Either zephyr skin or tan pouch leather can be used to make the
pouches.  Both have advantages and disadvantages, and the size of the
bleed hole in the bleed cup you use may depend on which you select or
on whether and how you seal the pouches.  For organ work applications
requiring tan pouch leather, I'd prefer using thin kangaroo skin, if
you can find it.  Kangaroo is much stronger and more durable, although
it does require sealing to make it airtight when you use it in place of
thin pneumatic cloth.

For gaskets, I would not use the cork-rubber ones sold by PPCo, even
though they come pre-cut and ready to use.  Much nicer gaskets can be
made out of gasketing leather, which is a delight to see and touch.

There has been occasional discussion and debate about the kind of wood
used by Wurlitzer to make its valve blocks.  A common architectural
wood used in this part of the country -- and Wurlitzer was located
in this part of the country -- is gumwood.  I bought some gumwood from
a local salvage company and made some valve blocks of it.  When
shellacked and finished, those blocks had the same soft, warm, brown
color that Wurlitzer blocks do.

On the subject of wood, it is a fact that North Tonawanda once rivaled
Chicago, even passing it one year, as the leading port in the U.S. for
lumber importation.

Matthew Caulfield,
Irondequoit, New York