Vintage German Pyrometer
The optical Pyrometer was first developed by Siemens & Halske in the early 1900's. It was designed to measure the tube-component temperature via an optical comparison of the "red" temperature of a small heated tungsten wire as small as 3 to 5 uM thick. At TAB, we use vintage Pyrometer's to determine the temperature of tubes in working microphones to determine if the unit is working with specifications. They also can be used to measure the temperature of a tube in a microphone with unknown specifications, like the Western Electric 47a that Oliver reconditioned.
The Pyrometer pictured on the left is the exact type used at the Telefunken Tube Plants in Ulm and Berlin made by H&B. The Pyrometer on the right is an East German version that was used at the various RFT tube plants. The one shown in this picture came out of the tube plant in Muehlhausen and was made by Pruefgeraetewerk Medingen Dresden.
Technical Drawing of the H&B Pyrometer.