Quote:
Originally Posted by Notimetolooz
I thought you built old_coot88's version and I guess you built vts1134's.
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Yes, I built what vts1134 posted, with a couple of changes. I used a 5K pot rather than 3.3K, because that's what I had on hand. I also changed the output capacitor from .002 mfd to .2 mfd, and changed R23 on the TV chassis from 5.6K to 56K. Here's a sketch of what I built, with some labels
The preamp/inverter seems to work well using either a 9V or 12V battery.
As for powering it from the TV chassis rather than a battery, old_coot88 suggested:
Quote:
Originally Posted by old_coot88
You could rectify it right offa the 6.3V heater supply using a single diode and a filter cap. That's assuming one side of the supply is grounded. It would give you real close to 9V DC.
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I tacked this together using parts on hand:
Using only one filter cap produced a faint moving hum bar, so I added a second. The preamp/inverter seems to work at this lower supply voltage (around 7.5V DC), although so far I haven't looked at anything except test patterns.
This is an interesting experiment, but I don't know whether I'll install this preamp/inverter. Yes, injecting the video produces a somewhat better picture, but the improvement is incremental, not night-and-day. In its current condition, the TV makes a watchable (although not perfect) picture without injection, as seen in this photo and video clip that I took a while back.
http://antiqueradio.org/art/DuMontRA...inaryInput.mp4
(The horizontal bands in the video are camera artifacts.)
I've been slogging along with this project for a VERY long time. It would be nice to get this whale off my workbench and putter with something else for a change. Maybe I'll put the TV in its cabinet and try watching for a while. If I can't live with it, I can always install the A/V patch later.
Thanks,
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html