al4 we38 tube Telefunken Germany DRP mesh plate double cup getter test strong power tubes 1930's 

one tube al4 Telefunken Germany DRP old production

mesh plate 

double cup getter bottom 

tested strong on tube tester Funke W19S = 26mA (reference good at 18mA) 

very rare version of this power tube, old production 

type Power penthone for last stage audio output  

AL4 = OSW3103 = A4FF4 = TAL4 = 4E1 = WE38 = NLP61 = RAL4 = 4L4 = N41_Topf-P8A = UAL4 = 4A26_Ultron = TL44

Other class quality (otherwise equal):   E2dIII ; GRDVI

Different maximum ratings:   4684 ; AL4/375

Heater different:   AL3 ; EL3N

Other base and other heater:   APP4B ; EL11

First serieJan.1936 Telefunken-Zeitung Proberöhren für Versuchsaufbauten 1935

Socket type Europe side contact P8A (Au P, 8SC) (Codex=Seo)

Filament Heater Vf 4 Volt / If 1.75 Ampere / Indirect / Specified voltage AC/DC

After high-gm output penthodes were launched in the UK as early as 1933, this new genre of tubes came to continental Europe in 1935, as the AL3 appeared by Philips, with a round (cylindrical) cathode and a gm of 9 compared to 2,5 mA/V of earlier types as a new standard in Europe which remained until the end.

In 1936, Telefunken launched the almost identical AL4 with an improved profiled cathode, first as a normal output penthode, then as beam power tetrode with beam confining electrode just like the 6V6, later as tetrode with open plate wings on each side and only two rods as suppressor “grid”.

Philips and Tungsram then renamed their existing AL3 also into AL4 and continued producing it unchanged.

In 1938 the new output tubes Telefunken EL11 and Philips EL3N appeared, equipped with an improved cathode and grid arrangement, which led to reduced heater consumption.

After this the AL4 was produced by Philips and others in the same electrode design as the output penthode EL3N or by Telefunken as their then output tetrode EL11 without any mention or change in the name, e.g. to AL4N or otherwise

box 177