My CT-100 lost HV (from losing one B+ line).

[Penthode]

Was the fuse replaced with a slow blow fuse? The slow blow will much better handle the surge and is recommended for most sets. Also reducing the rating below 0.25A especially if non-slow blow is asking for it to blow on switch on.

To better troubleshoot, I would suggest temporarily putting in a 0.5A, let is run and quickly investigate what is wrong. My guess is likely the slow blow 0.25A will fix it.