KM1 met gloeiende hspbuizen, weer een stapje verder (Algemeen)

door Maurice , Dordrecht, 27.08.2008, 18:55 (5933 dagen geleden) @ Gert Wouters

Ik had wat opgeslagen in mijn TV reparatie documenten hoek,

Misschien wordt het wat duidelijker de werking;

COLOUR COMPLICATIONS!!

The EHT requirements for the early colour sets were much higher than for monochrome, typically 25kV rather than 15kV. Line Output and Efficiency diodes became larger (i.e PL509 and PY500) and the DY86 was replaced with the larger GY500. An addition was the Shunt Stabiliser Triode valve. PD500, which regulated the EHT. In the Bush Dual Standard Colour sets such as the CTV25 series, focus voltage was also derived from the Line Ouptut Transformer and rectified with a DY86. Focus voltages themselves were in the region of 5kV.

This is a valved Colour TV Line Output Stage. The basic principles of operation here are the same as for monochrome albeit on a much bigger scale! Note also that this stage also provides the supply voltage for the frame stages and the A1 Voltages on the CRT.

For correct colour representation on bright and dark picture scenes, the EHT currentneeds to remain constant. Note how the Boosh HT, as well as providing the A1 voltages via D1 and the unrectified frame supply via R7, also biases the shunt stablilser triode valve V4. EHT current is adjusted (if necessary) with preset R9.

With all such stages, it is important to follow the setting up procedures descibed in the Manual and to avoid the temptation to judiciously twiddle the pots. Weak spots are the Valves themselves (a cautionary note: do avoid cheapo chinese replacement valves here if at all possible, there are still plenty decent types knocking around and be wary of second hand valves here apart from to prove a fault), the LOPT (I’m afraid) and capacitors. Another thing to look out for is a clean and sound connection on the Top Cap (Anode) of the EHT Rectifier valve V3 (GY500). A bad connection here can result in reduced EHT, poor regulation and can even be a fire risk. Check this carefully!! The Bush Dual Standard Colour Sets were known in the trade as the ‘Burning’ Bushes and with good reason so beware!

Many such stages are shielded and in the case of the G6, the stage is disabled when the covers are removed. The PD500 is also shielded. Not only does this valve dissipate 30 Watts but it also emits X-Rays. So do please treat these circuits with respect!!