To emulate a regulator failure, I use a LM317/338 with a suitable diode between it and the load, I adjust the LM317 for 0.7V higher then the design goal, use a suitable resistor (or 2N3055 rigged to draw the right current as an active load), a SPST push button switch connected to a 24V 10A power supply.
The crowbar is after the diode.
Push the button and you place 24V on a 5V/6V/9V/12V (13.67V) 'rail'.
Oh I have a variety of DC magnetic circuit breakers that open faster then a fast blow fuse will blow.
If the OV crowbar works properly, the SCR turns on and the circuit breaker opens.
I've blown the epoxy top off some SCRs.
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This is after testing the OV crowbar with a series light bulb and an adjustable DC power supply.
Slowly increase the voltage and note where the OV crowbar fires. The power supply dips for a moment then returns to the set value.
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I rebuilt the power supply for the R390A/URR (24V nominal, 26.5 optimal) and included a OV crowbar.
Because the receiver is connected to a ~100 foot random wire antenna, even on calm afternoons, a stray breeze or insect landing on the wire can induce an extremely short transient that will trip the OV crowbar if you don't have a delay capacitor.
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The R390A/R392 are fine receivers but you need to be Arnold Schwarzenegger to tune them. There is one knob for kc another for mc, the receivers have gear/cams inside that can give you quite the workout. They are great for dedicated monitoring of a single frequency, not so friendly to a 73 year old who likes to tune the band, jumping from one frequency to another.
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I loaned it [gave it really as I have zero intention of taking it back] to a younger member of our shortwave club who loves it.
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For TTL/CMOS/ Perseus, etc, I try not to have transients on the Vout rail. Try really hard and generally succeed. My failures were with pre 3 terminal regulators. Trying to roll you own precision 24V power supply with limited knowledge was a learning experience. Fortunately my V+ in was 30V so the R392 tolerated short mistakes with no magic smoke escaping,.
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