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Light Sixer transistor video amp mod?


Shawn
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  • 1 month later...

You could use a variable resistor. Connect center wiper to the transistor base and one leg as input in place of fixed value resistor. Turn it while the game's running until the picture looks good, then shut it off and remove the variable resistor without changing the value. Using ohm meter, check the resistance between the same 2 legs you used to get the value, and look for closest standard value.

 

Also I've seen some mod that has 75 ohms resistor on output and some with 100 ohms. Depending on TV, it may work with 100 instead of 75 or other way around.

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Here's some pics I took of the simple transistor mod I did on a 4-switch woody a little while ago.

 

WP_20151028_001.jpg

 

WP_20151028_003.jpg

And I drew up a quick schematic of the transistor mod for you ;) Tbh though, I have to agree unicycle. The simple transistor mod isn't the best way to go if you want good video quality. You'd be better off doing something like the CD4050 based mod.

But here's the schematic anyways.

Untitled.png

 

 

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  • 2 weeks later...

Pretty sure 75 ohms resistor needs to be in line with video out, not to ground.

 

 

Aye it does

 

 

You guys need to check again. Emitter needs a 75Ω pulldown. At least according to every I've ever read and on the 2600 I've composite modded, that's how I wired them.

Edited by SwampFox56
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all its doing is pulling down the video signal and keeping the transistor from sucking too much current though it, if your going to have one there I would think you would want one much stronger resistance, the TV is going to have a 75ohm impedance to ground as well

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all its doing is pulling down the video signal and keeping the transistor from sucking too much current though it, if your going to have one there I would think you would want one much stronger resistance, the TV is going to have a 75ohm impedance to ground as well

 

I actually thought that as well when I was first looking up the schematics people had drawn up for the simple transistor amplifier (I was breadboarding the circuit at the time), and anything over 100Ω's caused a drastic reduction in the black to white ratio (or Luma) and made the picture look awful.

 

In fact, you can actually go without adding any pulldown on the emitter, but that makes the picture A LOT brighter. You would think that would be a good thing - but honestly? I've found it depends on the console. From the eight 2600's I've worked on so far, about a 1/3 of them, I removed the 75Ω pulldown.

 

It would appear (in my opinion) that not all 2600's were created equally. Some need the extra increase in Luminance.

 

Something I haven't tried is adding an electrolytic cap (negative to negative, and positive to positive) to terminate voltage at the end of the emitter. But, I've never found it necessary on any of the 2600's I've worked on. Which leads me to believe that the composite signal itself needs the pulldown, and not a reduction in voltage.

Edited by SwampFox56
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I want to try 2 75ohm resistors in series from the emitter to ground and try tapping out from where the 2 resistors "join" to see what the results might be.

 

Won't be able to try this for awhile, anyone else what to give it a go?

 

You could just wire a 75Ω resistor, and a 150Ω resistor in parallel, and just disconnect one when you want to test the other. But as I said above, anymore than 100Ω's, I've found wrecks the contrast of the picture.

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  • 2 weeks later...

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