All the AB763 amps (Deluxe, Vibrolux, Pro, Super, Twin ) have signal oscillating tremolo while the Princeton and Princeton Reverb have power tube bias shifting.
The tremolo effect is huge in the Vibro Champ and allows you to go deeper and slower than on the AB763 amps.
Below is the original Oxford 8ev speaker of our 65 blackface Vibro Champ.
As with all vintage Oxford speakers you cannot expect lots of volume, punch and power.
The video below demonstrates a 1965 Vibro Champ The difference between the Champ and the Vibro Champ is the tremolo and not the vibrato.
The Blackface Champ and Vibro Champ (with tremolo) was introduced in 1964 after its presuccessor, the narrow panel tweed Champ, had been produced nine long years at Fender since 1955.
It adds and subtracts very little from your guitar tone and, unlike the bigger blackface amps with reverb, they do not distort much when they are cranked.
They remain pretty clean all the way up to 10 but with farty bass notes and some waspy speaker distortion, not very different from the Fender tweed amps.
This means that you’ll get good bang for the buck with a silverface amp.
Also, smaller and lighter amps like Champs and Princetons have stood the test of time much better than bigger amps.