View single post by Dr. Heinz Doofenshmirtz
 Posted: Dec 8th, 2014 05:29 AM
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Dr. Heinz Doofenshmirtz



Joined: Nov 17th, 2013
Location: Liberty, Missouri USA
Posts: 300
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 Cheap no name TV was basically brand new in its box at a local thrift store. TVs were 50% off that day. I paid $2.50 for this thing.....figured I would eventually do something with it....has a big tuning dial on the side...so i figured it was air cap tuned.......It has been in my car trunk for six months....brought it in......cracked it open......first thing i saw was an air cap tuner.....bout put the thing back together because I've never swapped the air tuner for varactors before...to much to get into on a Saturday.

I decided to look around in there anyways.....I noticed the air cap was for the built in AM/FM tuner.....if that was the case....wheres the dude for the TV tuner circuit.....The gear assembly went down a few gears and on the bottom one, it was a potentiometer....followed the trace to an RF shielded box.

Frank was right.  Alot of these puppies are VT, at least this one was.  As for the 30V sweep.....nope.....I used my standard textbook dual opamp triangle wave circuit modified for 9v single supply, and sub 1Hz output....not exactly sure how slow....1Mpot/100uf slow..... slow enough I can catch the Weather emergency boadcast on the UHF....Which seems to be about middle of the sweep....last time i fooled with a radio that could tune those freqs in, it seemed to be in the middle of the band somewhere......so... close enough. Im thinking of putting the Brightness Contrast and V-hold controls on strobes via separate oscillators driving LEDs/LRDs to complete the circuit .......