Quote Originally Posted by Firebottle View Post
The one problem with the valve output stage is that the HT voltage is only 75V, it is regulated which is good but it really could do with being higher to get the best out of any valve. The actual voltage across the valve is only 62V which only exacerbates the problem.

As it is only a buffer and is at a high signal level the regulation isn't necessary, so I removed it and simplified the filtering to achieve 90V across the valve.

Strangely (?), all of the valve buffer type arrangements I have come across don't run the valves very hot. Usually they aren't even hot to the touch, merely warm.
Is there a reason for that?

Jolida DACs come to mind. A few others as well.