HeathBuilt EU-80A Voltage Reference Source: History, Restoration, Demonstration, Theory

In this video, I describe the HeathBuilt EU-80A Voltage Reference Source, which is one of about 15 special 'factory built" pieces of laboratory and test equipment that the Heath company produced specifically for the college/university/technical school market, including the "Malmstadt-Enke Instrumentation Lab" set and the "Berkeley Physics Lab" set in the late 1960s and early 1970s. This EU-80A replaced the original EUW-16(A) Voltage Reference Source (see my video on that). This product is Zener-regulated voltage SOURCE (NOT a power supply....it cannot deliver any appreciable power to a load) with a set of precision voltage dividers that let the user control the output voltage from 0.01mV up to 10V. It can also be used in sum & difference mode, comparing or adding the internally generated voltage with an externally applied DC voltage. It came with a "Voltage-to-Current Accessory" (see my other video on that, coming soon) which allows converting this device's output to a current, as low as 0.01nA and as high as 10µA, useful for testing/calibrating certain ammeters, etc. Here, I talk about the product's history, its place in the overall HeathBuilt series, and I demonstrate it in operation. I also show the restoration steps I took and I show a small 'hack' that I made to make it easier to adjust the voltage regulator tube and Zener diode currents. Timeline Table of Contents: 00:00 History 05:44 Overview 14:37 Testing 19:25 Demonstration 29:08 Fixing the lowest voltage range circuit 32:01 Other restoration work 34:48 Beauty shot 35:09 Manual (overview) 55:18 Schematic diagram & circuit theory 1:24:15 Preview of the "Voltage-to-Current Accessory"