[Hybrid tellies]

Some dual standard black and white televisions use to give good 405 line pictures with good contrast and sharpness whilst on 625 the pictures tended to look grey, washed out and some suffered weak sync on certain picture scenes. They also suffered vision on sound effects on 625. Our GEC rental set was a good example of this and was why we continued to watch BBC1 and ITV on 405 rather than on 625.
A lot of this was I think down to the use of mean level AGC for both systems and AC video coupling to the CRT with no DC or black level.

The two best dual standard black and white TV's that produced good pictures on both 405 and 625 were the Philips 210 and the RBM A640 which used DC coupling from the Video output to the CRT with the RBM A640 using a kind of black level correction circuit.

Its interesting to note that the RBM A640 also had an interlace control in their frame timebase circuit. Some engineers told me that this was because RBM could not produce a TV with good interlace!