If you can, please post photos of your harmonica, of top side, bottom side, and mouthpiece sides.
There were 4 different models of the Trumpet Call series, made between 1906-1931(?).
Your 2-sided Hohner #426 Trumpet Call harmonica was made from circa 1912-1931, in Trossingen, Germany (at the Hohner factories).
Your Trumpet Call harp has 32 double holes on each mouthpiece,and measures 6.25 inches from left to right on the mouthpiece. It is a tremolo harmonica, probably in the keys of C (one side), and G (the other side).
Tremolo harmonicas have two horizontal rows of holes on each mouthpiece. Each vertically paired set of holes has the same pitched reeds, but one of the paired reeds in the vertical set is slightly de-tuned at the factory. When the two vertically stacked reeds are played together, a wavy tone (tremolo) is produced.
Your #426 Trumpet Call harp is known as the "Oriental Beauty," for it's single raised trumpet and the oriental man's face, on the brass covers of the harmonica.
There was also another #426 Trumpet Call, made at about the same time as the Oriental Beauty (1912-'31). It had brass covers with 2 nymphs playing trumpets, with the trumpets facing the left and right sides, and measured 7 inches left to right.It was double-sided, in keys of C and G.
Another Trumpet Call was seen only in a Sears Catalog of that era (1906-1913). It measured 7-1/2 inches left to right, and had 24 double holes, one side only.
The most famous Hohner #220 Trumpet Call harmonica was made for the 50th anniversary of the Hohner Harmonica company, in 1907-1931. It had 5 solid brass trumpets(horns)attached to the audience side of the harmonica. It was an octave harp, like today's Hohner Auto-Valve Harp. It had 10 double holes, and was a one-sided harp. It measured 4-5/8 inches from left to right on the mouthpiece.
The #220 Trumpet Call was re-issued in 2006(?),with gold-plated plastic horns. It's in the key of C.
Your Oriental Beauty has great sentimental value because it was your father's. It is also a rare harp, coveted by harmonica collectors and players. It's $ value is whatever the seller and buyer agree is a fair price. You could probably insure it for $500.
Please keep your Oriental Beauty (unless you need money), and learn to play it. We can help you with that, here at the Harmonica Club. There is a great method book for your study of the tremolo harmonica:Tremolo & Octave Harmonica Method
, by Phil Duncan, Mel Bay publisher. It includes a CD. I'm not an employee of any harmonica company or music publisher.http://www.melbay.com
You will be sustaining your father's memory for future generations.