11-02-2017, 10:56 AM
The anode feed does actually come from somewhere else, so the screen probably is lower than the anode in this case. I have often been told that the screen V is always less than the anode V, and agree that it should be, but it seldom is! Most of the circuits I have seen in Radio & TV servicing books, the screen goes straight to the HT+ line, the same as the top of the output transformer.
That black thing, top left is the 100pF aerial series capacitor.
In the image, it is me that "got at it!"
I took the bolts out of the double tag strip and bent it back so I could get at the components. When I put replacements in, I did not bother about doing it neatly, my first priority being to make it work again, which I have done. When it is working properly, I can set about tidying it up!
Regarding the V3 cathode bypass capacitor. This is an area where I got it completely wrong through not investigating fully what was happening. The circuit showed that it was 25uF, and I only got a few pF. At that time, I was unaware that one of the leads to my capacitance meter had become open circuit inside the insulation, and the reading was, of course, between the broken ends in series with the 25uF in the set. Once I fixed the lead, and tested the capacitor again, it showed 63uF. I removed it, and found that 50uF was written on the casing, so someone had replaced it in the past. I put a 22uF in place of it, and no real change in the performance.
But here is something for those more knowledgeable that myself, and I have not investigated it further, because we are going out shortly. I had an EF39 in the V2 position that had no metalised coating at all. I happened to touch the top cap, and immediately, the volume increased, the tone improved and the set became 100% stable! No whistles or screeches. I tuned across the whole band with finger on top cap, and the performance was absolutely perfect. Remove finger, and whistling and shrieking again!
Bob
That black thing, top left is the 100pF aerial series capacitor.
In the image, it is me that "got at it!"
I took the bolts out of the double tag strip and bent it back so I could get at the components. When I put replacements in, I did not bother about doing it neatly, my first priority being to make it work again, which I have done. When it is working properly, I can set about tidying it up!Regarding the V3 cathode bypass capacitor. This is an area where I got it completely wrong through not investigating fully what was happening. The circuit showed that it was 25uF, and I only got a few pF. At that time, I was unaware that one of the leads to my capacitance meter had become open circuit inside the insulation, and the reading was, of course, between the broken ends in series with the 25uF in the set. Once I fixed the lead, and tested the capacitor again, it showed 63uF. I removed it, and found that 50uF was written on the casing, so someone had replaced it in the past. I put a 22uF in place of it, and no real change in the performance.
But here is something for those more knowledgeable that myself, and I have not investigated it further, because we are going out shortly. I had an EF39 in the V2 position that had no metalised coating at all. I happened to touch the top cap, and immediately, the volume increased, the tone improved and the set became 100% stable! No whistles or screeches. I tuned across the whole band with finger on top cap, and the performance was absolutely perfect. Remove finger, and whistling and shrieking again!
Bob
