Introduction: 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.
7 Comments
7 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
Reply 7 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.
10 years ago on Introduction
how much volts on the high voltage?
Reply 9 years ago on Introduction
Sorry for the late reply, I think it is about 275 to 300V.
10 years ago on Step 2
I like this.
Where did you get the cathode tube?
All of mine are over a foot long and six inches wide.
Have you seen my Instructable, Building a Digital Oscilloscope from a DIY Kit?
https://www.instructables.com/id/Building-a-Digital-Oscilloscope-from-a-DIY-Kit/
Reply 10 years ago on Introduction
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.
Reply 10 years ago on Introduction
Cool I was looking at another Instructable they got there tube from an old video camera.