A full rake wouldn't require one since they were vacuum fitted and so the entire rake was sufficiently braked.
For example here:
https://www.flickr.com/photos/lickeybanker/11529707055/in/photolist-iyQLdF-dV2Zn6-299rETf-otd91u-WWUaQn-2ac2Wpj-boY9EH-6EvqkE-4F9BS3-79dnqr-dQQgf9-S4LGox-b14c4p-81TE5C-6Uhabc-2az6mhb-5JiiyW-dj3FsU-WvEpKu-dNUQXy-8c4Abp-r1kAac-pRuJZK-o6V9ch-qvULCF-ow6Da2-o1dJDK-vE5Fx-bZAeFJ-onF7EQ-PdtjtM-aXYUDr-VEFHEs-dJa4ag-p7sfso-iV7fQb-2aLDPvb-9Fb15F-nZUzy-Hq3WX5-8dGLGD-oGvWT1-8BTXab-28SCKDX-pUnguB-dyxbxu-68GYJG-DqHGcZ-4DQLjY-o5ou2B
That's also true for a mixed rake of different wagon types if they are all vacuum braked like Turbots.
For example, Turbots and Grampus:
https://www.flickr.com/photos/lickeybanker/33049110260/in/photolist-Smrk4S-depPba-8Ky9bB-7Wd7jG-9EWrPN-34oaHx-pPPdoj-9FeFjm-depQrc-9FaC4H-5XU9Y5-TygM1K-pPKytF-XgkWVV-7b7YYk-XdyAK7-otnGD6-4fGxvN-7W3MU3-7Wa5dV-pPQvMW-21Qatrs-fSXnP2-7ZQEA9-YvKibw-XgkWj4-fdZnAs-SsvmZp-9Fdhzo-9MAVd3-pxizC5-8DSYaM-9EU3Ee-jmiz4G-9FcWuj-7WcLwQ-7c3rQB-fkH5Qn-drmwJ2-9FbkoA-pxg6rR-k85myY-depuJE-ebfHxb-oSU5D3-nZpZjg-dEFEkd-bTUaNR-csdu5A-9FctcE
However, it they were marshalled in a rake with unfitted wagons then, yes, a brake van would be required in all cases. A quick search didn't yield a suitable photograph as an example I'm afraid.