[78-L] Deutsche Grammophon and Tempo questions

[Harold Aherne]

A couple of queries in my quest for knowledge about the German record industry:
 
Does anyone know the approximate month that Grammophon began electrical recording? Here's a Paul Godwin medley on DG 19536 that certainly sounds electric to me:
http://www.youtube.com/watch?v=7FJvGmm4QPU
 
--but this Dave Caplan side from ca. November 1926 (DG 20789, and about 320 matrix numbers later than the above sides) sounds a bit more acoustic:
http://www.youtube.com/watch?v=SsLIN37lZu4
 
Also, at about what number and month did they retire the full-colour Nipper and «Schallplatte „Grammophon“» in favour of the simpler drawing and just «Grammophon» ?
 
Tempo has been used as a label name in several countries for labels focusing on varied material, but it was also the name of a German label operating from at least 1932. Can anyone tell me its starting and end dates, and what label(s), if any, it was affiliated with? (or was ultimately purchased by ;^)
 
-HA