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Tube Tester design: High Voltage analog switch / mux, and other aspects
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amyk:
Tubes are high voltage low current devices (except for the filament) --- I would use relays, because then there's a far lower chance of a bad tube destroying the tester.
BrianHG:

--- Quote from: amyk on January 07, 2019, 11:23:03 pm ---Tubes are high voltage low current devices (except for the filament) --- I would use relays, because then there's a far lower chance of a bad tube destroying the tester.

--- End quote ---
Miniature latched telecom relays would do the trick (optional latching type allows a single power shot, then no power needed from your digital logic supply making super low power draw overall).  Today, from China, these are dirt cheap as well.  Though, a proper design with the opto-mosfets I mentioned above with current limited supply or series resistors to prevent maximum current of the mosfet switch devices.
T3sl4co1l:
PhotoMOS relays may be of interest.  Guessing the capacitance and leakage won't be a problem (compared to a mechanical relay).

Doing it with discrete MOSFETs, you'll need two in series, source to source, with an isolated gate driver.

You may want to handle heater connections separately, maybe with mechanical relays.  The combination of on resistance and voltage standoff is not so semiconductor friendly.

Tim
Ian.M:
Switching 400V isn't so easy, even if you can do so at zero load current, as you need a reliable >>400V isolation rating between contacts.

It may be worth looking at rotary switches driven by RC servos.  You could do the switches 'multimeter style' on your PCB, with gold plated contact pads direct on the PCB and a common arc or circle, the servo mounted direct to the PCB on the other side, with ts shhaft through a hole and a multi-finger phosphor bronze moving contact on a 3D printed arm on the servo shaft. Silver plate the moving contacts or solder on pure silver sheet on the tips before slitting them.  That would make it easy to do N way switching with enough clearance and creepage distance for 400V.   Shut down the HT and heater supplies before moving the servos to minimise contact erosion and inter-contact tracking across the insulation.
TimNJ:
I don't know anything about this project, but Steven on the Macrofab podcast just finished building a tube tracer.

http://analogeng.com/2018/09/11/utracer-3-upgrade-part-2-design-overview/

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