[TYPO3] How do I disable the RTE for the HTML content type?

[Pieter]

Hello,

on my Typo3 3.8.1 site the HTML content element is opened with the RTE 
for some reason (htmlArea).  Not so good because of the transformations 
in the RTE.  How can I disable this?

I have been looking at the typoscript and the page/user TSConfig but it 
is a mystery up to now...

Pieter