10-11-2019, 11:38 AM
(09-11-2019, 02:14 PM)Craig Wrote: Not sure what you mean by "Inferior Tektronix Curve Tracers". But whatever, I was just attempting to be helpful.
Earlier ones that don't do -Ve gate with +Ve drain, ie BJT only, no depletion mode FETs up to -19V in and +1400V out! I did have to read the manual twice to realise that there was a magical combination of settings suitable for valves.
No, I appreciate the info and I've saved it. Interesting review of valve testers and curve tracers. The circuit he has shows a 0 to +5V input (or even 0 to 0.5V) for +1V to -50V out which means it suits ANY transistor curve tracer.
Obviously with almost all valve testers the most useful bit is the heater supply, though a bench PSU is possible. The 2nd most important thing for tetrodes, pentodes, hexodes etc is a +HT screen voltage. Few people have a HV bench supply. I keep meaning to make a variable one for up to 1000V. Or at least 250V using and old radio transformer HT winding. Though a shaver transformer will do 250V @ 15W, or about 500V using a doubler.
I do have a fixed 85V HT (smoothed but unregulated, that's at 10mA load) test unit.
I have Dekker's uTester which does valve curve tracing and can do Depletion mode FETs. It's not good for heater supplies below 6.3V generally and mine is worse because the large number of sockets are AVO style wired. I should have had a single connector and plug-in adaptors. I will probably change it so that I can also have a plug-in for LC feedback to create oscillators and measure mixer/osc conversion gain and LO leakage at RF grid. It's because the uTester uses PWM of a laptop 19V to 20V PSU for the heater. It's also unsuitable for direct filaments, so I use a bench PSU or a separate 0.7 to 2.2V supply. It only provides pulse voltage for screen and anode via 2x SMPSUs from the Laptop PSU, however continuous current is enough for a Magic Eye. There is a mod for the uTester to do +Ve grid, needed for valves used at 13V HT in car radios and to test enhancement FETS or BJTs.
The Tektronix uses continuous voltages so a 10 amp 1200V FET or BJT needs as much heatsink as the application! The uTester can test transistors at hundreds of volts without a heatsink as it's using pulses, if they are depletion mode, or any N type if the positive grid modification is added. Unlike the Tektronix, the uTester is inherently unable to provide -ve voltages other than on the grid socket.
I've had it a little over 6 years. It's rarely used.
The supplies from the uTester and separate low voltage filament supply are the 2mm sockets on two rows, bottom right.
Small stackable patch cords are used to the circular array of sockets and two sockets for top caps that are wired in parallel to all the valve bases and TC sockets. All the connecting wires are in a complete loop like an AVO panel with ferrite beads on the wires. That's AVO's theory to avoid oscillating valves.
