|
Made some major progress tonight. First, I got the alignment looking pretty good, so I decided to try it out. I set the tv to ch3 hooked it to a pair of rabbit ears, and fired up one of my B-T modulators transmitting on ch3. ... But the picture was worse!
Before, I could only get decent video with a modulator hooked directly into the set, with the output cranked. But I had put that down to the alignment, and that weak 3rd IF tube I found. And even so it still had poor contrast. ... Now, the video was not only poor contrast, but negative, white was black, black was white...
After a few hours of searching I found the problem, when I recapped the set, I hooked the .1mfd cap coupling the two triodes of the 12AU7 video amp, one side to the resistor after the cathode of the 1st half of the tube, rather than coil after the plate. Fixed that and now it works good.
I still want to mess with the alignment a little more. And I need to solder back in all the resistors I pulled up to test when I was looking for my video trouble.
Probably all that was wrong with this was the weak 3rd IF tube, the cap shorting that coil at the 21MC trap where the sound comes off, and that other cap I soldered in the wrong place. I probably really didn't need to do the complete alignment, but I'm happy I did, because I've wanted to learn how to do it for years, and I think the overall performance of the set is much improved over what it would have been had I didn't. I can go all the way from one end of the fine tuning range to the other and still get picture and sound and not loose sync, I've never had a round-tube era b/w set performing this well.
|