How can you extend the life of your battery tubes
J. Pastor, Radioamator i Krótkofalowiec, Rok XI, march 1961

  Having often difficulties with the purchase of electron tubes for a "Pionier" type battery receiver, I was wondering how to extend the "life" of these tubes. It occurred to me that if the filament voltage of those already worn-out tubes working under normal conditions was increased by about 0.4V, their work should improve. So, losing nothing, due to the used tubes, I used 1.8V instead of 1.4 filament voltage, and I kept the anode voltage unchanged. These tubes started to work like almost new again in all wavelength ranges.
  After 360 hours, I increased the filament voltage again to about 2.4V and the work improved again for about 320 hours, so the total work of the tubes was extended by about 680 hours, which is one sixth of the warranty standard. I used dry cells to power the tubes, connecting two in series with each other - one new cell with a voltage of 1.4V and the other - used cell, with a voltage of 0.8V. I connected a 5Ω wire resistor to these cells in series.