Audio Research Corporation writes: “Got tubes? When our owner said that we have tubes, he meant it. A large shipment of Tung Sol KT150s, 6H30s and KT120s arrived late last week and we are burning them in now. (The boxes below the fixtures are full of KT150s that will also need to be burned-in.)
“Earlier last week we received a large shipment of tubes from JJ in Slovakia.
When new output tubes arrive we put them in our custom fixtures and burn them in for 48 hours. We do this to stabilize the tubes, burn off excess gas, and weed out bad tubes. Trasconductance and cathode current can change, and they measure differently. We pull the tubes from the fixtures when they are hot, measure them immediately, and the measurements are written on the base of each tube.
Different products require different grades; we do not know what the grade yield will be until we measure them. We are getting caught up on tube set backorders now as the appropriate tubes and grades are entered into inventory.
We need a pool of about 300 KT150 tubes to create a complete tube set for a pair of Reference 750SE mono amps because the 16 output tubes in each amp need to be tightly matched. The same is true for Reference 600 or 610T amps, which need a pool of about 300 6550s. After that, putting together a tube set for a Classic 60 or a Reference 75 is a breeze.”