Ken's Multiple Tube Tester 2026

8 Nov 2026 

This project is currently under development. This site will be updated as the design evolves.

Requirements of the device.

1/ Test 12AX7, 12AU7 and 12AT7 twin triodes four at a time to allow easy comparison and matching. Simple results on a two line LCD; detailed results via USB to any common terminal program.  Tube types can be mixed, the device handles it automatically and names the tube type.

2/ Identify the if the tube is a 12AX7, 12AT7 or 12AU7 at a glance if the writing is worn off and unreadable.

3/  Make tube comparison easy for non technical people. It will be easy to see the gain difference and  mA between tube brands operating under the same conditions.

5/ Key operating conditions from the GE tube manual can be replicated.

6/ Test the tubes as they are run in typical amplifiers.

7/ Use cheap easily available affordable components including a 3 D printed enclosure.

8/ Power the device from a 12AC 1A plug pack (wall wart). I intend to to fit 7 pin sockets for 6J6’s as I have quite a few and will the power it from a 72VA 12VAC garden lighting transformer I have.

9/ Include an audio amplifier and speaker so the tube noise can be heard,  tapping the tube can test for microphonics. BTW this feature is not on the first PCB design.

Many hours of spice simulations were conducted before the PCB's were designed. 

The testing is going well.  

The power supply has insufficient head room and drops out of regulation, a different transformer is required. To keep the tester cheap and repairable an Arduino Uno was chosen as many millions have been made and a clone costs less then $10.00 . A simple 2 line by 16 display shield with buttons costs about $12.00. BTW I will normally view the results on a laptop. The other boards have been designed by myself and so far seem to work fine. As the Arduino Uno only has a 10 bit ADC B+ the plate voltages measurements only have a 0.5 volt resolution, the cathode voltage has a 10mV resolution. The gain is measured using a 250 microsecond pulse to the grid. The 10 bit ADC reads the anode pulse.  The grid drive is variable and calibrated to enable a good reading from the ADC. The grid pulse has 3 preset levels, it starts on the middle level and changes after the first read if required.

I googled how many Uno's have been made including clones and it has surpassed 10 million units. The code is written on the Arduino IDE in C++. 

When finished I may well place the entire design and code in the public domain.