EXOTIC COMPONENTRY IN THE MULLARD HIGH SPEED VALVE TESTER

At the time of introduction, two 'hollow state' devices the MHSVT contained were considered exotic.   The first, the 85A1 voltage regulator is a neon filled reference two electrode device which serves to provide the MHSVT with it's reference voltage stable in normal useage to 0.17% variance and over it's entire life. stable to within 0.5% of nominal value.     The second is the DG7/5 cathode ray tube which is an electrostatic medium persistance tube .    What is interesting is that this CRT is used in this application purely as a voltage indicator, measuring various currents by means of voltage drops across resistances brought into circuit by the punched card valve selectors.  No need for a timebase here you see.    

With the passage of 60 years or so, opinions change and now we consider a CRT and a neon regulator rather passe and instead become animated if not rather excited by the EL37 beam tetrode that a MHSVT also contains - more on this desirable audio valve in a future blog entry.