Our customers have spoken, and we've listened. Get premium performance at an economical price with these new and improved spectrum tubes featuring improved spectral clarity. Please see the alternate product photos for a spectral comparison between our new premium spectrum tubes and our old line of tubes. These tubes are designed to fit most standard spectrum tube power supplies, but will also allow the user to wire them to any high voltage supply in the 4-5 KV range thanks to the included end cap clips. These premium spectrum tubes feature a large 4" / 10cm capillary viewing area in the center.