Possible Fix for Contrast Buzz?

[Electronic M]

Originally Posted by cluelessgame

I've been reading about contrast buzz lately. It plagues two of my sets, my Motorola 21BT130BE-1 and my Majestic 70, and I predict my Bendix C172U will suffer from it too once restored. Has anybody developed a fix for this? According to an older Antique Radio Forums post: (http://www.antiqueradios.com/forums/...ic.php?t=64442)
Modern televisions (relatively speaking) use SAW filters in their IF stages to eliminate this issue. I haven't really found any information of what exactly they do/how they work (or any schematics other than block diagrams). Would it be possible to build and/or add one to a vintage set?


the post also mentions in that this issue mainly stems from modern RF modulators not exactly conforming to the 12.5% minimum rule. would there be any way to possibly add some sort of regulator to the modulator output to fix it there?

Check/adjust AGC settings n your sets first (too high can cause or worsen contrast buzz) if that fails...

Just pop for a better modulator. Get a Blonder Tongue AM40, AM60(ideal for transmitting wirelessly to your sets), or a BAVMz family modulator, and adjust it properly....With a video signal containing high contrast text(most prone to causing buzz) turn up the video level pot on the modulator till it buzzes then back it down till just slightly past the point where it stops. Last I checked BT modulators could be had on ebay in the $20-40 range working...Much cheaper, easier and safer than trying to re-engineer 2+ TVs IF systems.
Granted some BT mods need the Power Supply lytics changed, but it is still much harder to fubar a lytic swap job than to fubar the IF alignment on a TV...Don't fubar your alignment...Fixing alignment will cost enough in specialized test equipment to make a bunch of BT modulators seem cheap.

I run all three BT modulator families I've mentioned and can adjust all of them to work excellent with no contrast buzz.