Mullard, a British manufacturer once called Mullard Limited, once specialized in components for myriad electronic equipment, from TVs to observatories. But what they're known for in the world of music is, of course, tubes. Both NOS tubes, produced half a century ago or more, and newer tubes, like the reissue of the EL34 produced by new owners Sovtek, working under the New Sensor Corporation, can be found on Reverb to give you a tone boost.