Cooltron Pedals
Introducing the Cooltron series of effects pedals, three very special stompboxes that use a 12AU7 preamp-type tube at low voltage to deliver the kind of tone that, until now, would have been impossible to achieve in a battery -powered pedal.
Normally, tubes are used at high voltages and this restricts their use in battery-powered devices such as guitar effects pedals. Historically, attempts have been made to use tubes at low voltages in what has been dubbed " starvation" mode, but these circuits don't allow the tube to function in an acceptable manner. The tube simply cannot be biased to a satisfactory operating condition. Plus, the necessary heater (filament) current is too high to deliver acceptable battery life. Imagine how annoying it would be to have to change batteries every ten minutes during a gig !
Here's what makes the Cooltron system tick. The Cooltron circuit basically operates by using two very special signal paths. The first is the "servo circuit," which provides the right conditions between the plate of the tube and the grid. This achieves controllable, stable parameters for the tube and provides the correct operating conditions for the tube to function as it would run at a higher voltage. The second circuit is a patented power supply that provides a low voltage, low current supply to the heater elements in the tube. Since the tube is now running at such a reduced supply level, the anode current is much smaller than normal. This means that the amount of heat required at the cathode to achieve sufficient cathode current emission is much smaller - hence the ability to run the heaters at a lower level and for Cooltron pedals to run for 20 hours on 4 x AA Batteries.