ADF can only be tuned in ANT. mode

[some1]

It should be possible to tune the ADF in every available mode (COMP, ANT, RAMKA). There is no mechanical lock that would prevent the tuning knob from turning. The real MiG-19 manual explicitly instructs to tune the radio in COMP. mode during system checks:  

 

 

The manual also does not contain any additional instructions that would advise pilot to change modes every time he needs to change frequency, like we currently have to do in Razbam's model. In real life, tuning ADF in ANT. mode may still be a preferred method, because it amplifies the audio signal, so it's easier for the pilot to find the station frequency and verify it's the correct one. Even more modern digital radios like the one below have such mode. But that does not prevent it from tuning directly in compass mode. 

Edited February 23 by some1