VTA ST-120 amp with tubes glowing blue ... Certain types of output tubes will emit a violet/blue glow while the amp is playing. This is perfectly normal and does not mean that the tube has a problem or is gassy inside. The blue glow is actually a type of FLUORESCENCE in which the interior of the glass is hit by stray electrons when the tube is on. The glow is easier to see if your listening room is dimly lit. The photo showing the "blue glow" on a matched quad of Sovtek 6550's was taken by VTA amp customer Jeff Francis from California. He used a Pentax 645Z digital camera at F11 with a 6 second exposure @ ASA 1600 with a 60 mm lens. Nice work Jeff ! Beautiful photo !
