Fender Bassman 135 head has great tone and v clean for guitar or bass, even with everything above 7 on the gain and master.
You can jump the channels to get extra grit and bight too.
The old 70s MusicMan 150 head is great too; though pre-amp is solid state, which is NOT a bad thing; sweet tones mostly come from the power stages of valve amps anyway.
Another one to check out would be a Burman head, also from 70s - that has both more clean, more tone and more dirt (if so desired) than anything on the planet and often incredibly good value for the money; although people are starting to get wise to these overlooked classics.
Any of the above would come in at under £1k and only increase in value and probably be more reliable than any modern gear too.