I've had a number of people ask me to make the DC filament supply boards I made for an earlier project available. I've finally gotten around to it...
You can use these to provide DC power to a tube filament or heater, or you can use them for any general purpose DC supply. You can use two to get a bipolar +/- supply as well.
I made the PCB the same size/shape/mounting as the Tentlabs supply, so you can try this one (constant voltage) and replace it with the Tentlabs voltage-controlled-constant-current supply without any modifications to your amp.