The early tv sets here in Germany did not use a D.C. amplifier due to problems with varying video drive currents. They instead had D.C. restoration, coupled with the brightness control.
This technique was also applied in early color television in 1967, see for example:
http://bs.cyty.com/menschen/e-etzold...T2000color.TIF
Saba used color-difference concept with D.C. restoration.
On the other hand, the Einheitschassis, made by Telefunken, Blaupunkt, Siemens, Nordmende, used D.C. amplifying circuits in the video unit with RGB concept, see
http://bs.cyty.com/menschen/e-etzold...hassis1967.tif
For keeping the D.C. drive or bias constant, some additional circuits were neccessary.
The early Metz color tv sets used color difference concept with D.C. amplifying:
http://bs.cyty.com/menschen/e-etzold...metz6285-1.TIF
The best picture quality I get with the Saba (color-difference concept with D.C. restoration).
Color difference concept with D.C. amplifying and D.C. amplifying with RGB concept are the best, but does only operate best with an absolutely strong crt. Saba with color-difference concept with D.C. restoration does work well even with a weaker crt.
- Eckhard