Changing channel on RF modulator

A new crystal, a bunch of new capcitors and inductors to tune the output to the proper channel and bandwidth. You need a spectrum anaylyzer to do it right. Or you could just pick up a used CATV or MATV modulator that's already on Ch 6 or an Agile modulator.

Here is an agile modulator with a single $9.99 bid:

Agile means that it is programmable to work on any analog TV channel.

There are 88 on Ebay while I type this.

Interesting. Two answers, Two totally different opinions I looked at the Ebay units and it seems you can pay $100 for a known good one and $10 or less for a broken one. (if it says "untested" it was tested and it failed or it came out of a dumpster, probably both.)

I did look inside and there is just a sealed silver RF can with 2 adjustable inductors behind holes in the can. I am not sure if one is Ch 4 and the other Ch 3 or they are two stages of one modulator. (the former being easy, the latter being a perfect paper weight generator without some test equipment I don't have)

Sorry Prot, no "adjusting pot".

The only other parts in there are for a crude DC power supply.

I was just giving you the options. Also, by law the unit has to be certified to meet the FCC requirements if it's modified. I've worked with RF most of my life, starting with building a radio at eight, and being a broadcast engineer at four stations. I've worked in two way radio, Cable TV headend & distribution, MATV systems and manufacturing of high end telemetry equipment for multiple US government agencies. There are options, but if you want a decent picture, go with a real modulator. There is a working BT agile modulator for sale cheap on news:rec.antiques.radio+phono, but it's in Korea at the moment. There is a tread about Antique TVs, started in the last couple days.

Not really. A lot of this stuff is now obsolete after the forced switch to HD TV. It is being pulled out of CATV headends as more digital channels are added. Some people don't have the manuals or brains to program an agile modulator to test it. Blonder Tougne has always been helpful when I needed a manual. Sometimes the equipment was over 15 years old, but they always had it.

If it is like the units I've worked with, each coil goes to a single crystal to pull the crystal to the proper frequency.

Generally, pots are for setting video & audio modulation, but newer modulators are built to better specs, or the pots are somewhere else in the equipment

That really depends. I've taken a gamble on quite a bit of "untested" gear on ebay. Some of it was broken, some of it worked perfectly. Most of the broken stuff was simple to fix, usually power supply issues or cracked solder joints at connectors. Some of it was junk, but in the long run I've come out far ahead. I've also sold untested gear that was truly untested, I did not have either the knowledge or other required parts of the system to thoroughly test it. Personally I would buy a cheap untested/broken one in good cosmetic condition and fix it up, it's easier than trying to modify a consumer unit and you will have a piece of professional broadcast quality gear when you finish.