Great care and effort goes into the vacuum tube compliment selected for each Tenor amplifier. Tubes are chosen for a specific amplifier design based on a number of proprietary elements primarily related to frequency response, harmonic content and microphonics. Many of the tubes are New Old Stock (NOS) … but not always. There are some beautiful modern made tubes which fulfill all of our objectives for greatness so we try to select the best of what is commercially available regardless of age. Of course, the importance of reliability and availability is paramount otherwise that brand of tube will be rejected. Once a tube brand has been selected for a particular amplifier model, we buy in sufficient volume so we can undergo a rigorous tube selection process whereby large quantities of tubes are “ burned in” under the exact conditions they would experience in their amplifier circuit. A good representation of our tube farm is shown where Gilles is testing tubes which have undergone a “burn in” for anywhere from 200 to over 700 hours depending on the particular tube’s idiosyncrasies. We go to great lengths which many companies would find unimaginable. We do it because it is necessary to make a great product … and you can hear the difference!
Following the prescribed “burn in” all tubes are then tested for the usual normal specifications such as continuity, emissions, mutual conductance following which they are sorted in groups that match the circuit specification requirement of a Tenor perfectly. In the context of Tenor tube matching, we are not always concerned with identical tubes but rather tubes that compliment the role they play in each circuit. Preamplifier and Phono Stage tubes are tested for even more stringent specifications. Noise is the main culprit - generally referred to as microphonics - so Tenor developed a proprietary noise tester where we bombard quartets of tubes with white, pink and brown noise and measure the impact on an oscilloscope while listening for noise in headphones. The reject rate varies on the tube type and the application but on average we reject up to 50% of tubes tested at this stage!
In the more general practice of typical manufacturers, microphony, if tested at all, is often determined by the simple flick of a tube once it powered up in the amplifier attached to a speaker. Not very scientific and certainly not sufficient for a Tenor amplifier. Tenor has taken the precision of “tube testing” to an order of magnitude beyond everyone else! All of these elements contribute to the performance of a Tenor amplifier and how we can warrant tubes for 5 years or 10,000 hours. Most definitely this is the best tube warranty in the business! Tenor has also advanced the reliability factor of tubes so far that retubing an amplifier with a Tenor tube replacement kit may never be necessary in an owner’s lifetime! After all, 10,000 hours at 3 hours per day is almost 10 years of continuous music - which on a Tenor is worth its weight in gold!
Each Tenor amplifier has a compliment of tubes selected for a number of proprietary elements. The table below summarizes the tube types used for each Tenor amplifier.