This is a follow-up to the discussion in MMD last June and July about
a replacement motor for a Welte Vorsetzer.  It also applies to any Red
Welte piano, where two pump motor speeds are required.

For $119.95 + shipping, a surplus house is selling a Minarik XL3025
adjustable speed drive for DC brush motors, either shunt wound or with
permanent magnet field.  (A compound wound motor can be made shunt
wound if the connections to the brushes are removed and DC voltage is
applied directly to the brushes.)  If a suitable motor can be found,
this would seem to be the way to go.

The unit works from 50 or 60 Hz lines, 115 or 230 volts.  On 115 volt
lines it delivers armature voltages from 60 to 150 volts DC, and on 230
volt lines 60 to 240 volts DC.

Since excessive voltages could damage the motor if something went
wrong, it might be advisable to provide overvoltage protection.  The
same surplus house sells for $1.50 a magnetic latch relay, item
T351X-41 the release coil of which could be connected in series with
a series string of 1 watt Zener diodes (these are very inexpensive) to
open the circuit (through another relay, the latch relay does not have
sufficient current rating) if an overvoltage condition occurred.

The Minarik unit is for motors up to 1/4 HP (1/3 HP on 230 volt
supply), and the maximum armature current is 3 A.  The acceleration
time is adjustable from 1 to 12 seconds, and the only problem I can
foresee is that the fastest acceleration time might not be enough to
have the motor up to speed when the roll calls for fortissimo.
However, this time is for acceleration from stop, and the acceleration
from the slower speed should be considerably less.  The punching of
Red Welte rolls obviously allowed for whatever acceleration Welte
motors had, with a margin for error.  And the reservoir will provide
some energy while the motor speeds up.

A very complete user's manual is supplied, with connections shown
for switching between two preset speeds.

The unit can supply field voltage to the motor.  Unfortunately, the
only voltages available are 50 or 100 volts when working from a 115
volt line, or 100 or 200 volts when working from a 230 volt line.
Probably none of these will be what you need, but it would be quite
easy to build a suitable field supply.  Even easier would be to build
a booster unit.  For example, if your field requires 115 volts, you
could build a small 15 volt supply, and connect it in series with the
available 100 volts.

The unit uses pules width modulation technology.  This makes it very
small and light, but unfortunately it means that the outputs and
control circuits are not isolated from the power line.  Also, when
considering the risk of electrocution, DC is more dangerous than AC
of equal voltage.  Therefore, the work should be done by, or under the
supervision of, someone used to high voltage work.

I have only just received my unit, and have not yet done anything with
it.  I wanted to get this information in MMD as soon as possible,
because they may run out of stock.  I have no idea how many units they
have.

The surplus house is Brigar Electronics.  Their address is 7-9 Alice
St., Binghamton NY 10934, their phone (607) 723-3111, their fax (607)
723-5202, their e-mail BRIGAR2@aol.com.  They publish a catalog.

Cecil Grace