This evening I stumbled across a really good deal on a Cobra 29 LTD Classic CB with a Astatic 636L mic. Everything worked, so I gambled and picked it up. It was made in 1992 and has the side mounted mic input consistent with that era. The strange thing that I can't find any info on is that it has an extra knob on the left side with 3 positions labeled L, M and H. Out of curiosity I opened the CB up. Someone has definitely been inside, as there is a stamp from Hitch'n Post Radio in Dodge City, a couple of dates written in marker and what appears to be an added dial wrapped up in electrical tape. Anyone have any ideas about what may have been done to this thing? I'm guessing it's been tuned at least once, but I've got no idea about the extra parts.

In my best English accent; "But you see, this one goes to eleven.'

Just a guess, there used to be a lot of internal modifications back in the early 90's Some of them were dont to protect a CB from being overpowered from too much signal. I remember some guys I was based with in a CB club telling me that sometimes a truckers CB would have an illegal program or (system) in their CB that could key the mic and fry anything within a specific distance away from the semi. They used this to have the ability to talk to each other over longer distances and that L,M,H could designate various frequency settings as well. Low Medium and High.

probably side bands.

Took the CB into Summit Radio. Looks like someone put a decent amount of money into this thing. The Channel 9 switch now makes the unit send out train sounds when the mic is keyed and reverb was also added. His best guess about the random side dial is that it is additional channels.