Glad that this subject was brought up.......
Since the 70's:
"Locked":
* To me, the clarifier has always been "locked" by/from the factory by FCC rule for all new 40 channel radios. There by being right on the TX ("locked") and RX (unlocked) with clarifier at 12 o'clock. BUT over time things change, and Golden-Screw-Drivers make changes ..........
If a SSB radio having a "locked" clarifier is tuned properly, it only needs a clarifier to clear up the RX. Due to drift on many radios with "locked" clarifiers ("Friends don't let friends talk on Galaxy radios."), many radios need to warm up, some going the other way as heat builds up.
Talking to someone off frequency with a "locked" clarifier you will always hear the same from others ...... "Get on frequency!" ... to which they couldn't and always say "Is that any better?" after turning their RX only clarifier .... to hear "NO!" from everyone. Then expected everyone to tune to them......... Some radios have access to the TX as a separate section on the clarifier and that's another mess in itself (best to be "unlocked" for both knobs to a Fine and Coarse).
"Unlocked":
* To get the clarifier "unlocked" by someone that knows how to "unlock" it,
there by properly being able to track RX and TX ....... both being on frequency.
* Then there is the option of "slide":
This was the start of the "slider", to be able to cover the frequencies between channels, by turning the clarifier counter-clock-wise, to include the "A" channels, which also all got "unlocked". This does not stop the warm up time for some radios, but the clarifier can be used in the mean time.
For those that understand I say no more ..... a clarifier does not always need to be at 12 o'clock position to be on frequency and we know why.
Best bet for any SSB radio ....... get it "unlocked"!
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New radios:
On my (the new) Washington Mobile 10 meter radio, as are, or should be many new programmable radios with a menu, and/or a hidden menu. I've never used the clarifier on CB channels, I have not used the "unlock" option due to its being on frequency from cold start to warmed up from day one (in VFO mode still no clarifier needed, but not to say it can't be used in "unlock" mode).
Due to my being a ham this changes on any of the ham bands, as there are no channels per-say just frequencies ...... a modified CB radio for 10 meters with a "locked" clarifier has no place on ham bands.
As usual .......... just my 2¢