Hi forrest, Stephen, and all,
OK, here's my little Tombo Student 13 key box in D#/E. Stephen has usefully described layouts like these as "1.3 row" boxes. It was evidently played a lot, and is unrestored.
At first glance the box seems to have some similarities to both German and Italian boxes. Open button levers, plastic buttons, and "one row plus a few smaller helper keys" are all reminiscent of some little Italian organettos. The trim pieces, stamped metal grille, and the brass reeds on long plates are reminiscent of some cheap German boxes. But there are some interesting quirks to the design.
First, the button rows are a full 10 plus 3. The little Italian organettos I've seen with one and 1/2 rows are much more likely to have just nine buttons in the outside row. Then, the outside row in D# has what's called a "button 4 start" here on melnet.
The layout is a transposition of the one most often seen at the lower end of the rows on 23-key Irish boxes. On the Tombo that layout (shown as press/draw for each button) is:
D#/G# G/C A#/D D#/F G/G# A#/C D#/D G/F A#/G# D#/C
In my experience this layout is pretty unusual for the main row of a small box but actually is very useful for melodies that drop below the tonic note of that row.
For example, the layout of the main D# row on the Tombo is a transposition of exactly the most useful notes I would want for a 10 key box pitched in (high) G (as in the G row of a D/G box), to play the Irish tunes and songs:
G/C B/E D/F# G/A B/C D/E G/F# B/A D/C G/E
The inside helper notes of the Tombo are laid out in the key of E:
E/F# G#/A B/C#
Like the Irish American D/C# boxes with 1.3 row layouts, the layout of the Tombo provides one octave that is fully chromatic.
Basically, someone used to playing a C/C# or a D/D# box based on the outside row would find the fingering for this Tombo very familar. As all the reedplates (4 treble, 2 bass) and the keyboard edge are stamped "D#" we know that that's the intended key reference. The pitch is around A 444.
PG