Hi.
Can anyone tell me how to set mp3 as the default output for ripping cd in k3b.
Thanks

You don't say what distro, what version, what version of k3b, or what you are seeing so it is impossible to truly say what the issue is.

You know, I hope, that mp3s are not from an open source codec and thus may require a 3rd party app be installed to create/read mp3s.

Can you select mp3 as the type file to create when ripping? or is that not possible and the cause of your question?

When I use k3b for ripping I select mp3 as the output file type and it automatically remains as the setting until I change that. I also have lame installed to support the mp3 codecs.

First, ensure that required packages are installed
Do you see an MP3 plugin in Tools ‣ Configure K3B ‣ Plugins?

Or you can try the K3b External Audio Encoder as described here. The article is about m4a, so you'll have to adjust the FFmpeg command line accordingly. I guess something like
should work. For details, see the FFmpeg MP3 Encoding Guide.

Thanks for your replies.
My apologies for not making the issues clear.
Distro is Ubuntu MATE 20.04. (I assumed this issue is distro agnostic.)
MP3 is installed and working correctly.
Each time I put in a CD and go to rip it K3B defaults to ogg. (This is no good as I am sending the CD to someone who will not know what that is.)
I have gone into settings but can find no place to set the default to MP3.
Maybe it is not possible.

It is certainly possible.
On mine (k3b version 20.12.2) I insert a CD, go to 'tools -> rip audio cd -> start ripping' then in the window that opens up the upper half has the track listing and the lower half has 3 tabs. There, under the 'settings' tab is a 'filetype' button that produces a drop list from which the file type is selected. When I select 'Mp3(Lame)' then click the button at the bottom left corner of the window it saves the current settings and it remains at that setting until I change it again.

I don't think that has changed over the many years I have used k3b. It is a users choice to save the settings or allow it to always open up a previous (possibly even default) setting. The second button on the lower left corner allows the user to revert to default or open up one of the previously saved settings as well.

I don't think that behavior is specific to version because it has stayed the same for the many years I have used k3b.

Many thanks. Solved!