Passive EHT indicator (Overview)

Overview (Passive EHT Indicator)

Principal Design goals:

-To accurately measure 'floating' (i.e. non-ground referenced) DC EMFs to 100kV. (Zin=800MΩ).
-To accurately measure positive or negative ground referenced DC EMFs to 75kV. (Zin =400MΩ).

-To achieve stable readings via: Grounding of cabinet and contents (including the d'Arsonval movement) --in all operating modes-- and full electrostatic shielding of the d'Arsonval movement.

-To assure meaningful readings via presentation of the 'circuit-under-test' with a (Ca. 250%) 'heavier' load than provided by commonly available 'high voltage probes'.

-To provide greater EMF range and power handling than available from test equipment intended for servicing of CRT display systems.

-To enhance electrical 'ruggedness' in EHT environments via eschewal of semiconductor components (with the sole exception of the movement protection 'clipper').


Please note: that this 'installment' is an overview only! -- The primary functions of which being familiarization of the reader with the instrument's 'general anatomy' and sub-assembly designations! Please rest assured that minute details will be given in the (forthcoming) construction articles!


Schematic based upon the desirable dropping resistances / Typical d'Arsonval impedance.




Mode detail



Frontal view of assembled unit: (Note that improved d'Arsonval mounting will be presented in the construction articles).





Rotated view of assembled unit: Illustrative of the 'pole septum' assembly.



Front panel detail:
(Faraday shield dismounted).



'Mini-Fed' well and plug detail.



Interior view of 'Mini-Fed' Well.



Mini-Fed plug detail (Note the tape-wound PTFE 'alignment ribs').



Full view of test leads -- Test clips exposed.




Full view of test leads -- Test clips retracted.



Towers partially removed -- Note that same are attached to the cabinet assembly via threaded steel bolts.



Appearance of Cabinet assembly following removal of towers.



Tower port detail: Note top of PCV 'mast step' (to be shown presently) visible beneath grommet...




Appearance of uninstalled towers ('well-ends' bottom of image)




Appearance of uninstalled towers ('fastener-ends' bottom of image).




Interior cabinet view (perspective 1).




Interior cabinet view (perspective 2)



Interior cabinet view (perspective 3)




Mode selection/calibration subchassis detail.



Inasmuch as there seems to be some considerable confusion as regards the nature of the 'mast steps' - I have included the following draft by way of exposition...

Note that the 'receiving fasteners' are each fabricated of a steel hex nut soldered to the center of a 'fender washer' having an OD slightly less than the ID of the associated PVC end-cap (such that said washer is effectively 'pinched' between the end of the PVC tube segment and the 'breach' of said end-cap...

Installed positions of Tower components and chassis... Please note that ---for the purposes of this illustration--- cabinet and cabinet-cover are drawn as a single piece denoted 'chassis' below...


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