excellent stuff, CL, fascinating to watch the project progressing.
Chas 'n' Dave ............. how could you?
Cas and Dave live on, they just might be a touch more 'conductive' than before
Cant be a bad thing IMO
Anyway back to the project
Finally got the panel to work propery
. I have a slight hum, but the coating is too fresh and I may have to remove a few bolts to check for shorts, but basically I sorted it. I am however not going to cover that panel till I have done a couple of others just in case I decided I am not happy.
Since i last posted I have learned more than I ever wanted to know about ESL 57s. There are lots of how to tutorials on the net but none I found tell you how the panels are made up, and what can go wrong with them (the actual stator)and what to do if you have issues.. Typical, well I hope I can fill a few gaps. If you go back to the pic of the seperated stator so you are looking at the inside of it probably the best pic for this is the one were I have just fitted the new diaphram. The two centeral tracks going up the middle of the stator are carbon coated and they are connected to the foil track round the edge of the panel. When you clean the panel it is very easy to smere some of this carbon onto the inside of the plastic stator giving a connection or short to the grid part of the circuit. The three grids are coated on the OUTSIDE of the stator with conductive coating and then later sprayed with an insulating paint. The three grids parts of the stator are connected together at the bottom of the panel by a thin external strip (under the paint), but this strip does not connect the two central tracks or the foil edges as they are on the other circuit.
Now my problem was a few things, first I was not getting enough coating on. It is possible I have too much now but that is not a problem as I can always redo the panel, but I should be OK as you can have a stator resistance a low as 30meg but it will start to distort but will be VERY sensitive. Normally my coating will be over 400meg so even if it is half this it really wont matter a bit so I am not going to stress right now.
The conductive strip that links the grids at the bottom of the panel is too wide, this panel is the replacement panel from the 80s which has always fizzed and has always been of low output (why I started doing it first). This too wide strip goes low enough to touch were the holes are drilled and those holes were also drilled too close to the internal foil strip so the high voltage found itself a path through fizzing away shorting the panel. My fix was to slightly slot the holes down a bit and to with a craft knife cut moon shapes from the conductive strip near the bolt holes (not cutting the whole strip through of course) to increase the distance of the two parts of the circuit. There was yet another problem
The central connector at the bottom were the stator is charged (external circuit) was riveted at least an inch lower than any of my other panels. The area around the rivet has no paint so you have uninsulated external circuit right next to the internal lower foil track. I painted the exposed metal and also painted into the holes to ensure there could be no leakage. Another error Quad made is on the older original panels they stuck insulating tape behind this point inside the panel a patch around an inch and a half square. On this panel the patch was maybe a one cm by two.
I hope that is all clear and I hope it prevents anyone else going through the headache I did over this. First make sure you panels inside are spotlessly clean with no smeres and second look for possible shorts, I had 3 that were cracking that turned out to be bits of rivet left in the holes, check check and check again.