Mullard Pupil's Oscilloscope




This instructable describes the construction of a extremely simple 12v oscillosope.

The diagram below is a schematic of the Mullard pupil's oscilloscope.  This is a single valve (+CRT) oscilloscope that is about as simple as an oscilloscope can get.  The Mullard scope is described in the Radio Basics column of Practical Wireless March 2005.


Step 1: Transformer Winding

The transformer was home wound on a ferrite core that I had handy and an aluminium clamp fabricated to enable it to be fixed to the chassis.

Transformer Winding Details:
L1,L4 12 turns 26 swg
L2,L3 3 turns 26 swg
L5 450 turns 36 swg

Step 2: Construction

Below are pictures of the oscilloscope during construction and completed.  The scope shown above did not include the X attenuator potentiometer shown in the circuit diagram.  I also added a 68pF capacitor between the Y amplifier anode and the supressor grid of the timebase pentode to provide a sync. signal.



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    8 Discussions


    3 years ago

    A great example of how a minimalist circuit can work well. I have not built this CRO as I prefer symmetrical drive to the deflection plates to prevent trapezium distortion. Another advantage of such a simple circuit is that it will drive several different types of CRT's eg 902, 2AP1 etc. You may need to add a focus pot for the 2AP1. The OTK 13lO1i is a 1 inch tube but will also require a focus pot CRTGIRL100

    1 reply

    Reply 3 years ago

    You are correct about the trapezium distortion, however some tubes are designed to minimize this including the DG7-31 and DH3-91. The scope is not really that usable due to the small cathode ray tube and low bandwidth. The circuit will drive a DG7-91 with the addition of a focus supply, this was suggested in the original Mullard publication.


    3 years ago

    Nice build. Makes my Heathkit OS-2 look positively futuristic!

    Hi Josehf,
    I purchased the cathode ray tube from ebay for about £15 in the UK an alternative to dh3-91 is the 1cp1. Thanks for the link to your page I have seen this kits advertised and may buy one in the future.