So confused on electrical issues

I first saw colour TV in 1960 at the Radio Show at Olympia, where the BBC installed a studio equipped with Never-Twice-The-Same-Colour cameras and equipment, linked to monitors in a viewing area. They ran chat shows, panel games and telecine for several hours a day. One side of this area was glass beyond which was the studio, so you could  see Judith Chalmers in the flesh and on screen at the same time. When i was there the place was packed out. It was to be 7 years before I saw colour TV again. I saw 819 line TV when I first went to France in 1965, and I was struck by how much better it looked than the UK 405 line system. The set I saw in a café in Rouen showed really excellent black level and coupled with the high resolution, the effect was not unlike a well exposed and printed black and white photographic print.

Incidentally, speaking of French standards, Britain's 25 kV AC railway electrification system is very heavily modelled on the French system developed in the early 1950s, and HS1, formerly known as the Channel Tunnel Rail Link, is a French ligne à grande vitesse in every way. And let's not forget where the metric system came from.

I saw 819 line TV when I first went to France in 1965, and I was struck by how much better it looked than the UK 405 line system. The set I saw in a café in Rouen showed really excellent black level and coupled with the high resolution, the effect was not unlike a well exposed and printed black and white photographic print.

Poor black-level clamping really used to let down some cheap sets which otherwise produced a quite reasonable picture, along with poor EHT regulation so that the picture would expand and shrink slightly with the overall brightness of the scene. 

One of the things which really used to show up the 405-line structure was if the interlace was out a little so that lines from one field didn't sit dead central between the lines of the other field, resulting in line pairing.  It could happen with any line standard, but obviously was more noticeable the fewer lines you had to start with.   

The one drawback with the French 819-line system was the huge (relatively speaking) bandwidth it used, 14MHz per channel.  I have to admit that the overlapping, reversed relative positions of sound/vision carriers, and careful use of vertical vs. horizontal polarization at sites was an ingenious way to minimize such problems.   Some other places which adopted the 819-line system (Monaco, some overseas French colonies etc.) just took the 819 video and restricted the bandwidth, which rather seems to defeat the purpose of using the system if the horizontal resolution isn't up to the same standard as the vertical.

When it comes to power, I have to concede that at least France did the right thing by continuing its nuclear power program instead of half abandoning it as happened here.  Last time I saw the statistics a couple of years ago something like 75% of total French generation capacity is now nuclear.

poor EHT regulation so that the picture would expand and shrink slightly with the overall brightness of the scene.

Blooming. Tell me about it! When the emissive surface on the cathode of the DY96 eht rectifier valve was on the way out, it used to get much worse.

Did you mean DY86?  That was one of the most common types, along with the EY86 with its slightly different filament characteristics. 

I still have a box full of DY86s somewhere. 

Well, it had a 1.5 volt heater, so that's the D, a diode rectifier, so that's the Y, but I guess over 40 years I have become confused about the base. I was probably thinking of the DF96 battery pentode. What about the wire ended ones, e.g. the EY51? Ever see one of those?

Yes, it was a B9A base, not B7G.       



I've certainly worked on old sets with wire-ended EHT rectifiers, possibly the EY51 although I can't recall for sure.   Have you ever seen some of the old Murphy TVs of that era?  They were noted for having "unusual" circuit arrangements, especially in the power supplies, and right through to the late 1950s some of their models were still using a winding on the mains transformer for the EHT instead of deriving it from the line-output transformer.

Funny you should mention the old battery radios; I have an Ekco mains/battery portable that I'm in the process of fixing up at the moment:  DK92, DF91, DAF91, DL94.   As you may have gathered, I have a particular interest in older equipment.   

Oh, and here's another blast from the TV past: