Tube Amp Doctor (TAD) is a German company specialising in electron tubes and related components for musical instruments and audio amplification.
TAD is closely cooperating with all of the few existing tube factories. Their techs, who are all active musicians, have been developing processes to test and secure the quality, consistency and reliability of TAD tubes.
Tube Amp Doctor STR tubes (Special Tube Requirement) are produced to exclusive TAD designs and strict specifications.
Real tube quality control is way more than just a simple test. Before a TAD Tube gets accepted at all they perform extensive sample evaluation testing for consistency, power test, shock resistance test, soak test (long term operation at full power) and of course a musical test in known amplifiers to learn about its sound character with different playing styles.
The main tests are made after a proper pre-aging to stabilise the cathode emission. While most available tube test equipment runs at 250V as a maximum TAD built their test rig to operate at voltages of 360 to 600V depending on the tubes being tested.
Every Tube is tested by qualified staff. Each pentode is inspected, tapped while operating and listened for noise floor, hum and odd noise and finally measured for a set of parameters and matched by Plate Current (PC) and Transconductance (TC).
TAD do test batches of 400 to 500 pieces per run to allow tightest tolerances of typically 0.5mA for PC. All Tubes and boxes get labelled with the PC and TC test results and a unique serial number to identify every tube ever tested. Tube Amp Doctor also verify and monitor selected and matched TAD Tubes by using them every day in their own amp service department.
This is the most complete quality control system you can imagine which is what allows EAV to give a genuine 6 months warranty on every TAD tube installed in EAV’s workshop.
Why don’t you use TAD tubes?