That Darn DuMont Again

[bgadow]

This is the DuMont color set which has made the rounds of AK TV Heads & is now residing here. Just as I fixed a short vertical problem something else developed & I havn't figured it out yet. That should come as no surprise, I still have lots of learning to do!

I have a video problem (well, the sound is messed up, too) that acts sort of like its overloaded. Sometimes I can just about hold a picture though its not nearly correct. Its going negative, the sync isn't too good; I have been looking at the video amp & agc circuits. The agc control is basically just lightening/darkening the picture. Earlier it was working more normally, with an almost correct picture locking in at times with the control cranked all the way up. Now I pretty much have a blank white raster with occasional video getting in there. I get the same results tuning the local uhf station directly or through a vcr on ch 3. I have been searching for a bad solder joint or bad resistor but everything looks okay. I have subbed all the tubes that I suspect. Remember, this is basically a NOS tv set with just a matter of hours on the tubes, so I am not too quick to suspect them. I measured voltages on the 6KA8 agc/sync tube & the 6LF8 video amp tube. They are all over the place:

6KA8 pin 1 should be 130v, is 75; pin 2 should be 5, is 19; pin 8 calls for 130 but reads 68; 9 should read 30 but I show -11.

6LF8 lists 5v on pin 2, has -1; pin 8 should be 110, is 73; 9 is listed as 185 but reads 18v.

I thought about swapping the video detector diode. I don't know anything about them & what their failure would cause. I have a NOS ECG109 but can't tell which end is which. No markings, not banded like the old one, one end is grooved like the end of an electrolytic cap. I have an RCA 3088 that I think should work but haven't dug it out yet.

This is in Sams 1114-1. Another learning experience!