Interesting discussion. I was in Vienna recently. While I was there. I visited the museum of music that exhibits pianos of Mozart, Beethoven, Schubert, and others. Here are some photos I took. It looks that Beethoven’s piano does have more keys than Mozart’s. 
My traveling practice keyboard setup!
Like @thepianoplayer416, I have a Piano de Voyage. Besides the semi-weighted and spring-loaded nature of the keys that feels pretty weird when playing fast or light passages, the short key levers also mean that when you play up between the black keys, it takes noticeably more force to press the key down.
The pieces of the keyboard are actually just slightly large enough to be inconvenient to pack into a carry-on, so I still need to figure out the best way to carry all 4 pieces. A couple weeks ago, I brought along 3 of the sections totaling 63 keys on a short trip. That was mostly sufficient to practice notes for the Haydn Sonata I've been learning (minus a couple low Gs) but couldn't really do any more delicate work due to the nature of the action. And it definitely wasn't enough range to practice most of my rep.
"You're a smart kid. But your playing is terribly dull."
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WieWaldi Everything going from C to C is a keyboard: 25, 49, 61, 73 (octaves*12 +1)
Everything going from A to C is a piano: 76 and 88 keys (octaves*12 +4)
Oh, my mother's upright german Feurich isn't a piano or even a keyboard then. 
It's from the 1920's and has 85 keys (A0-A7). I don't think 88 keys became the more or less single standard in Europe until one or two decades later. Looking in this old catalogue from circa 1927 Feurich sold pianos with "7 octaves" (85 keys) as well as with "7 1/3 octaves" (88 keys) then. I also think many Asian piano factories (Yamaha among them) produced 85 keyed pianos much later.
WieWaldi I think 88 keys is maybe too much for a traveling keyboard.
Maybe. But I really think a person has to ask the honest question; "Do you play the notes that would be missing on a 61 or 73 or 76 note keyboard?" If you never play them, the answer is obvious. If you do play those notes quite a lot, a shorter keyboard may not be ideal.
There are a lot of players out there who really may not play all 88, ever. I ain't one of 'em. I'd play 108 if they were available. There have been a whole lotta times I've gotten carried away with a run, in either direction, up or down, where a finger hit the wooden cheek block of the piano where a certain key would be if it existed.
Used to torque me off when I was tuning pianos. One of the "45 minute wonder" tuners would completely skip the top octave to octave and a half on a tuning and remark, "nobody ever plays those notes anyway". Um, yeah, some of us do. He had his list of faithful customers. There was another list of customers that said, "never send him to tune my piano again".
I am using the Roland Go-Piano for airline travel. It weights around 8 lbs and can run on batteries. It has 61 keys. What I like about it is that it has a width of only 34.6 inch (87.8 cm), thus it fits perfectly into a duffle bag within airline luggage dimensions. And there are no buttons to break off.
Not sure if it has been mentioned already, but some of those keyboards including the Roland Go-Piano can shift octaves. I have used that feature occasionally and it works as long as the overall range of the song fits within those 61 keys. It took me a while to adjust to the shifted middle C, but it works alright.
Cheers,
MandM Both your Go-Piano and my Casio CT-S1 were on my shopping list on top-left position. I almost geared to the Roland because it has 4 cm less of width. Then I realized that all the cheap available transport bags are eating up that advantage. 
I totally understand what you like about it. The octave shift is of course a no-brainer feature for 61 keyboard. I use it quite often on mine. I just realized, Casio released my keyboard as 76 key version, too. Would I change if I could? Probably not, for practicing purposes 61 is still good enough, and I like the size. The 76-key version with 115 cm width would not fit that easily into the trunk of my car. I would need to transport it diagonal, eating too much space when I go for holidays with a lot of other luggage.
cheeeeee Thank you very much for posting this pictures.
Mozart's has 68 keys, ranging from F to C and
Beethoven's has 72 keys, ranging from F to E. (Can't see if the top note is E or F)
It is also interesting, that Mozart's has the modern white/black key scheme, while the picture above shows the colors inverted. (In the Mozart movie, he also played the black keyboard.) I did a short search on the internet, when this color scheme has changed but found nothing about it. Looks like in early Mozart days there was the black scheme, but in his later days it swapped. As Mozart didn't get that old, I can now narrow this down to about 1775 to 1790.
WieWaldi It is also interesting, that Mozart's has the modern white/black key scheme, while the picture above shows the colors inverted.
The instrument in the painting looks like a harpsichord to me. Even today a reversed color scheme seems very common for harpsichords, from my personal unscientific experience.
WieWaldi think 88 keys is maybe too much for a traveling keyboard. I have a 61 key Casio that weights about 5 to 6 kg including bag and all accessories
May I ask how you like about the action of this Casio keyboard? I’m considering the Casio S160 for traveling purposes but the Casio CT-S1 seems a more practical choice. Is the action as good as the regular models with 88 keys? Thanks.
I should've mentioned, that I brought my keyboard on a road trip in my car, and not a plane. Thus, easy to take with me. Otherwise, I would've brought nothing 
cheeeeee Is the action as good as the regular models with 88 keys?
No way. The CT-S1 and all other CasioTone models have a spring loaded action. The CDP-S160 uses a hammer action and plays in a different league.
Just think about it:
- CT-S1: 61-keys = 4.5 kg
- CT-S1: 76-keys = 5.3 kg
- CT-S1 (88-keys theoretical) = ~6.0 kg (or 13 pounds)
- CDP-S160 (88-keys) 10.5 kg
I think this gives a good description about all spring loaded key actions in this price range:
HeartKeys M-Audio Keystation 88. Terrible action but weights only 13 pounds, and powered by USB. And hey it’s 88 keys.
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MandM The GO: Piano is a very nice cheap and portable instrument. For people who like more variety in sounds there's also the GO: KEYS. Very comparable to the GO: Piano, but with less piano sounds and many more other sounds, such as e-piano, organ, strings, synths, marimba etc. Plus it has a fun built-in accompaniment mode and recording options. I think the keys of the GO: Piano are better weighted than those of the GO: KEYS though.
Sorry for the thread drift, but I have a question about this:
Bellyman Bosendorfer did extend that lower octave on down to the C below, which is kinda cool. Mostly, I see that covered up so that you can't play those notes.
Do you mean the keys that are all black? They're aren't covered up, right? As seen here:
Unless you're talking about a different piano?
Yeah, I don’t think they’re covered, but I don’t know why those keys are all black. I will make a thread in the acoustic piano sub forum (so I don’t derail this thread anymore!)
Oops, sorry, a little more thread jacking …
@Bellyman you were right, those extra keys used to be covered!
The extra keys, which are all at the bass end of the keyboard (that is, to the left), are colored black so that the pianist can tell them apart from the normal keys of an 88-key piano. They were originally covered with a removable panel to prevent a pianist from accidentally playing the extra notes.
Interesting! I guess the black color makes sense, but it doesn’t make sense to cover them! Like, are you going to flip that cover off in the middle of playing?
