Orange DIVO-OV4

All users amps all-tube "fixed bias" are subject to the same problem when changing power tubes: pass by a technician who did the "bias adjustment".
To make it simple, lamps amp generate a flow of electrons going from the cathode to the anode, and a grid placed between the two elements will regulate this flow, a bit like a tap. Adjusting the gate voltage allows to increase or decrease the flow of electrons (ie open or close the valve a little more): this is precisely what we call set the bias.
If the flow is too low, there is a loss of volume, the sound is dull and loses momentum.
If the flow is too high, the sound is very good but too hot lamps, which wears out prematurely.
Orange DIVO OV4 is a small box connected to 4 sockets that are placed between the power tubes and their location on the amp.
Self-powered, easy to install, this camera is mounted very easily in my head amp, and does all the work alone from the start.
But then what is it? Say it three main interests I class in order of importance (in my opinion):
1 / It continuously measures the electrical values ​​of each of the lamps, and isolates a pair immediately if a fault was found on one of the lamps (which avoids trashing output transformer for example).
2 / It constantly adjusts the bias of each of the lamps so that the optimal function. So, over the visiting tech '(savings), no need to purchase matched lamps (re-saving). Removing the old lamps are replaced by new and basta.
3 / More anecdotal for me, it allows you to mix lamp types, since it works for all types, or even via an optional footswitch to select a pair of EL34 and a pair of 6L6 for example from a his English a more American sound.

Difficult to assess as a tool that is relatively new and for which there is no competition, but I think it is a worthwhile purchase for those who want to be their own technician to the extent possible, and want secure operation of their amp.
The relatively high purchase cost will be amortized by the savings when changing lamps.