Military or post tubes are generally designed for long life service, independent from country of origin or dedication of use. So the early direct heated triodes for different professional applications, mainly for wireless systems were designed for long term flawless operation, compared with their standard consumer replacement types. Today I want to present a quite rare tube type manufactured for the early french military amplifiers (Télégraphie Militaire), the TM2. Made by Mazda this tube is technically almost identical to several civil types, like Phillips A409, A410N or the German RE 084 from Telefunken. Different to these equivalents the TM2 has a solid fixed metal shielding and a isolation made from foam underneath. The typical sensitivity for shock or electromagnetic stray fields of the direct heated tubes is minimized a lot. Together with its low heater consumption heating system of 0.08 ampere at 4.0 volts heater power, these special parameters make this tubes a wonderful device for preamplifier concepts. Comparing this tube with other DHT-Tubes like the 26 or 801, the low heater consumption makes the TM2 a very good alternative, because the heater power supply can be designed a lot simpler with several improvements in the daily use. The tubes are equipped with the typical european 4-pin socket B4 and their quite low Plate resistance make the tubes a very good alternative to other DHT's, because they can be implemented very well with output transformers available from the standard catalogue of the most brands like Lundahl, Tango, Tamura.
For people who are interested to see the inner construction of the TM2 here at Jogis Röhrenbude you can see it stripped down.
Keep on reading, Volker