Injecting video in DuMont RA-102?

[Phil Nelson]

Out of curiosity, I built that preamp/inverter on a piece of perfboard, using a 12V battery supply and a 2N3903 transistor:



It works, after a fashion, but it isn't great. The first pic shows the video signal (color bars) direct from the pattern generator:



And below is the signal coming out of the preamp. The pattern is inverted, but kinda "slenderized," and there seems to be some noise or instability:



The screen image is disappointing. It has decent contrast and detail, and the pot on the collector acts as a contrast control, but the vertical is quite unstable and retrace lines are visible nearly all of the time (not much in this pic, though):



I wonder if the 2N3903 transistor wasn't the best choice? The local supplier didn't have much to pick from. Here's the 2N3903 data sheet:

http://www.brown.edu/Departments/Eng...s/2N3903-D.pdf

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[miniman82]

Looks like lack of bandwidth if you ask me, did you sweep it to make sure it's passing all frequencies up to about 4.2mhz? Probably could use some peaking.