Bob Taylor gives a wonderfully concise description of the typical
variations seen in Steinway Duo-Arts over the years [120211 MMDigest].
However, I would emphasize his point that "one cannot say the word
'always'" when speaking of the Duo-Art."  In my limited experience,
it seems that most individual instruments deviate from the standard
timeline of changes in some details, most commonly with "earlier"
components retained in later models, but also somewhat perplexingly
with occasional "later" design details looking at home and apparently
original in earlier pianos.  Two recent Steinways I've restored may
illustrate this.

I'm just completing a full restoration of a 1927 model OR walnut
art case for a customer that mostly looks typical of the "post 1925"
design described by Bob.  It has the 80-note short stack, with poppet
rods aft and the forward-mounted stack located between the legs, simple
control levers without the Temponamic knob, round valve seats in the
stack, and the Una Corda action shift pneumatic.  So Bob's observation
that the art case pianos often retained the older features with the
full 88-note stack doesn't hold here.

Oddly, the una-corda valve box (supposedly a newer feature) was
equipped with a single old-style cross-seat valve rather than the two
round-seat valves I have usually seen.  However, the newer round valves
were found in both the sustain pedal and reroll/motor cutout valve box.

As expected for the later design, the spoolbox was mounted to the
cornice of the piano and not to the keyframe, and there is a connector
block pass-through mounted to the left of the keyframe allowing a quick
disconnect of 17 tubes for expression and control.

The roll transmission is the later style, simpler and more compact
with shorter chains, and lacking the idler rollers for adjusting chain
tension.  And the tracker finger valves are the later style also,
mounted inside the tracker bar with only short projections through the
bar, and with flush recessed adjusting screws in the face of the
tracker bar.

Last year I completed a model XR mahogany plain case with a 1920
serial number, that as expected had the earlier-style 88 note stack
with forward poppet rods and cross valves.  However, it lacks the
Temponamic knob typical of earlier designs and has the identical style
lever controls as the 1927 OR.  It also has the una corda pneumatic
(supposedly a later element), with dual valves, just as pictured in
the 1927 service manual.  It also had the spoolbox mounted to the piano
rather than to the keyframe as expected for early designs.

There were no extra screw holes or other "ghosts" suggesting that these
"later" details are in any way a retrofit.  Otherwise, it is typical
for 1920, with the larger transmission, externally mounted tracker
fingers, and all of the expression and control tubing passing through
the keybed with the regular notes.

It makes me wonder if Aeolian and Steinway may have started
introducing many of the "later" design variations long before 1925,
but were comfortable producing a mix of designs and components at any
given time, with the fitting each instrument by hand using the mix of
components that happened to be available at the moment in the factory.
And while they clearly drifted overall toward "newer" designs for many
components, it may not have been uncommon for an older-style component
to still be used as long as supply lasted.

Certainly, I haven't seen much evidence that they switched abruptly
from "older" to "newer" models.  So while the "LR" may have had a
definite date of first issue, it wouldn't surprise me if they continued
to produce "OR" models well after that.

Ralph Nielsen
http://www.historicpianos.com/