The goal is to have an as simple as possible while as performant as possible instrument able to measure vacuum tubes like diodes, triodes and pentodes.
The system is constitued by two parts:
1-A specific Power Unit to supply the tube in test and pick up values.
2-A dedicated Software to visualize, store and process data.
The PC Sound Board is used as analog to digital and digital to analog converter.
A taped transformer delivers 1.5, 2.5, 4, 5 and 6.3 Volts according to the patching.
A current source with .1, .15 and .3 Amps outputs feeds serial heated tubes, the voltage adjusting itself.
Control Grid Supply
An few watts integrated audio amplifier receives a near square 1Khz signal from the sound board, its amplitude being proportional to the expected control grid voltage.
This signal is amplified, steped up and rectified, then applied to the grid of the TUT.
Non linearities mainly introduced by the rectifier threshold are precorrected by software.
Screen Grid Supply
The same way is used, the voltage is switched off during each half mains alternance to reduce screen dissipation and to create a zero reference for screen current measurements.
A tapped transformator supplies a voltage selectable by a rotary switch.
It is full wave rectified but not filtered and feeds the plate of the TUT which thus swings from zero to the choosen value at twice the mains frequency.
After being scaled down, this voltage is sent to one input of the Sound Board while another voltage sensed in the return of the recifier and thus proportional to the current thru the tube is sent to the other Sound Board input.
So the software receives continuously the values of the anode voltage and of the resulting anode current.
Resistors inserted in the transformator primary limit the power dissipated by the TUT.
More to come