Regarding the bleed control screws in the Licensee mentioned by John
McClelland [001201 MMD]:

Jim Miller, one of the world's great scholars on the subject of
the Welte and other reproducing pianos (if also one of the least
appreciated), explained to me the importance of correct bleed
regulation in the Welte-Mignon, some years ago.  I believe that he
deduced this from the detailed attention given to the subject in the
T-100 (German Red-Roll) manuals, and his tests and superb results
confirmed it.

It is obvious that the disappearance of this attention from the manuals
of the American descendants of the Bockisch/Welte creation did not
derive from any engineering advances.  Careful measurements of the
Licensee expression valve bleed sizes reveal that the manufacturers
were well aware of their importance.  They are not always the same, but
more importantly, they are bored in microscopic sizes, almost unknown
in any other player instrument -- far smaller than tap drill size
#70!  I have had to pound standard bleeds nearly closed, and rebore
them, to achieve the needed sizes.

I'm not sure why an adjustable bleed would be more likely to clog up
with dust than would a disc or cup type (another reason the PowerRoll
is a better way to play automatic instruments: rolls are a source of
dirt for bleeds!).  However, it is not an easy task to regulate a bleed
size to perfection, when using fixed bleeds.  German Welte used blank
paper discs, then pierced them with a needle!  The hand bearing the
needle must have been a sensitive and steady one.

Why would bleeds need to be re-regulated, for example, in old Welte
instruments whose pouches had not been changed (they should be)?

Pouches do not remain the same with regard to porosity.  It is almost
certain that the factories sealed them with various chemicals, and I
have observed that these sealants decay over time, even when the pouch
seems good.  For those not up on these things, a change in a pouch's
porosity equals a change in its effective bleed size.

To achieve accuracy, anyone who owns a Licensee or Poughkeepsie
"Original" must regulate the timing of all of its functions with the
German test rolls and German manuals.  The tests for bleed-related
timing functions do not exist on the American test rolls, because the
factories assumed that the pouches were not old enough that their
porosity could have changed since manufacture.  That was many, many
decades ago.

How do you time a Licensee with the German test roll?

Use a recut of a German roll, translated to the American scale,
or ... use a PowerRoll.

Larry Broadmoore, Broadmoore Research Corporation
1709 First Street, Unit "C", San Fernando, CA 91340
tel: (800)497-4266 ; (818) 365-6231 ; fax: (818) 361-0911
http://www.powerroll.com for PowerRoll information.

PS: Also please see Michael Waters' excellent site about the PowerRoll
at  http://www.waterex.com.au/player/poweroll.html

 [ A needle valve has far greater surface area "wetted" by airflow
 [ than does a hole bored into a thin plate, like a bleed cup.
 [ That's probably why a needle valve is more likely to clog with dust.
 [
 [ The Ampico B, and probably some other systems, employs a fine-mesh
 [ screen to help prevent dirt from clogging the tiny #70 bleeds in the
 [ valves.  I wonder if the adjustable expression control bleeds in
 [ Ken Caswell's Welte player were similarly protected.  -- Robbie