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Terminology confusion

Kelly Marie Angel
Hi all the term medium voltage has as far as I know been out of favour for a good few years i think I'm right that any thing up to 999 volts is LV and anything above that is HV is this still the situation? I ask because I've seen a few videos and Web pages recently describing  medium voltage switch gear and equipment these are mostly pages that keep coming up now following my searches on power factor correction. Which in turn were a result of my post on large cotton reels in substation you now how it is a few mouse clicks and your into something else
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    Right at the end of the valve era, in a desperate bid to keep pace with semiconductors and the miniaturisation they offered, very small high gain  frame grid valves ('large' frame grid valves ) were made, exploiting all the photo-resist and etch techniques of the PCB lab to get really small clearances, so the anode voltage (HT) could be made low enough to compete with transistors of the day.

    Even before that the 1957 issue of the Mullard Technical Communications magazine shows a reference design for a car radio using  the specially made low voltage heptodes ECH83 for the RF front end and an OC16 transistor for the audio output.  (link  - here the HT is 12-15V depending on the car dynamo.)

    Actually if you do not mind micro ampre anode currents and high impedances then even the traditional large valves can be made to work, albeit with really low gain, at  much reduced HT - it is also quite possible to demonstrate thermionic diode operation at 12V with a headlamp bulb with one blown filament, or the dual brake stop lights. (use the connection to the blown part as the anode, and the bit that works as a cathode. Do not expect more than a few tens of microamps though.)

    Mike.



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    Right at the end of the valve era, in a desperate bid to keep pace with semiconductors and the miniaturisation they offered, very small high gain  frame grid valves ('large' frame grid valves ) were made, exploiting all the photo-resist and etch techniques of the PCB lab to get really small clearances, so the anode voltage (HT) could be made low enough to compete with transistors of the day.

    Even before that the 1957 issue of the Mullard Technical Communications magazine shows a reference design for a car radio using  the specially made low voltage heptodes ECH83 for the RF front end and an OC16 transistor for the audio output.  (link  - here the HT is 12-15V depending on the car dynamo.)

    Actually if you do not mind micro ampre anode currents and high impedances then even the traditional large valves can be made to work, albeit with really low gain, at  much reduced HT - it is also quite possible to demonstrate thermionic diode operation at 12V with a headlamp bulb with one blown filament, or the dual brake stop lights. (use the connection to the blown part as the anode, and the bit that works as a cathode. Do not expect more than a few tens of microamps though.)

    Mike.



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