Till Eulenspiegel wrote:From the Radiomuseum, details of the Osram U329: http://www.radiomuseum.org/tubes/tube_u329.html
The Mazda U251 is similar. If you looking for reliable replacement consider the PY88, 30volt heater.
Till Eulenspiegel wrote:In the early 1960s as a replacement for the often unreliable 305 barretter the GEC service department supplied a resistor fitted into the ES cap. The barretter itself was a clever device, it had an iron filament and the bulb was filled with hydrogen. The heater chain current of 0.3amp was maintained over a wide range of voltages.
Many pre-war radios employed barretters, for 0.2amp heater chains Mullard supplied the types C1 and C1C.
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