• There are very few tube factories in the world, GT sources only from the best

• GT only purchases raw tubes meet specs for low hum, noise and microphonics• Tubes are shipped to GT global facilities for further selection and grading• The first step is a burn-in period which lasts approximately 2 hours• This “settles the tubes”, burns off impurities and stabilizes components• All processes and computer programs are proprietary to Groove Tubes• House of Pain – The Human Element – Groove Tubes must make the first cut• Tubes placed in amplifiers hooked to hum / volt meters and speakers• Amps run at very high levels of Gain, EQ and “ping” tested for microphonics

• The Brain of the Black Box – Scientific evaluation of overall tube performance• Tone Generator runs a frequency sweep through an amplifier into the Black Box• Output from Black Box signal is connected to GT software and monitor

Fail - non-GT tube

Pass - GT tube

• The Brain and the Black Box – Scientific evaluation of overall tube performance• GT proprietary program tests for smooth frequency response, gain and output• Tubes are tested for hum and noise level, results are displayed in graphic form• The Kennedy Amplitrex AT-1000– Internal tube function revealed• GT proprietary program further dissects and measures tube performance• Evaluates plate resistance, current, voltage, bias draw, transconductance• The Kennedy Amplitrex AT-1000– Internal tube function revealed• Provides numeric values for gain and voltage for each triode• Based on results, tubes could be part of Special Applications Group kits• The Hagerman Vacu-Trace and 465-B Oscilloscope - The final refinement• Tubes are matched for Special Application Group kits during this phase• Matched Phase Inverter (MPI) tubes must pass this testUn-matched triodes

Matched triodes• The Hagerman Vacu-Trace and 465-B Oscillisocope - The final refinement• Provides visual reference matching for two sides of triode• The two curves must visually lay on top of each other to be a perfect match• Groove Tubes features proprietary matching and grading of power tubes• Tubes must meet the same rigorous manufacturing specs as preamp tubes• Tubes are placed in a fixture and “Dynamically Energized”

• Only Groove Tubes does “Dynamic Energized” testing of power tubes• Measures cathode filament voltage, plate voltage, wide variety of other specs• The GT “Mothership” contains all coding information on unique GT testing• Tubes are graded according to distortion levels on a scale from 1 to 10• Tubes with similar distortion levels are matched in pairs, quartets and sextets• This creates opportunity to properly bias amp to maximize tube performanceDate Code / Power Ratingon the silver base label
Month / Date / Year• High graded tubes have more headroom and less distortion - fine scale is 8 - 10
• Medium graded tubes most commonly used in stock amps – fine scale is 4 - 7• Low graded tubes are softest and quickest into soft clipping – fine scale is 1 - 3

• Overall display size is 6” deep x 12” tall x 16” wide - front is solid, back opens• Clear front and back, internal shelving holds power amp and preamp tubes• Works on a counter top or with standard 6” shelf brackets on a wall