Revisiting DL33 one electron tube power music signal amplifier

At your risk. All safety precautions should be followed. Any voltage or current can be dangerous. Also a suitable fuse must be connected in series with a battery to minimize fire hazard.


Setup:


Power of Goodbuy - Madonna from Ray of Light CD - Sony CD Walkman line out bridged to mono - Pleiades DL33 power amp with Sowter 1:7 input transformer and Sowter or Pleiades output trasformer - Pleiades linoleum Auratone 5C type cube monitoring speaker with 5in Tesla drive unit or Zeiss Ikon baffle speaker with Dew 7in drive unit


More information on previous posts.


Coupling of music signal to grid is with a capacitor.


Cathode is connected to ground. This is done by connecting the centre tap of the direct heater filament cathode to ground.


Grid is at space potential floating or returned to ground trough a 10MΩ resistor. Connection of 10MΩ to anode was also tried with no improvement in sound. Improvement happens when plate potential is very low, see Pleiades bias on Pleiades V6 microphone microphone booster amplifier.


The Pleiades output transformer is made of 2 ferrite Es separated by the thickness of a A4 paper on one side (one of the 3 areas of contract of the 2 Es) to create an air gap for avoiding magnetic satuation by quiescent DC of single ended class A operation. Size of magnetic circuit is about 5cm by 5.5cm.


The Sowter transformer is the much bigger SK05.


Filament voltage is about 2.5V.


Plate potential was increased to about 75V. The input octal base Sowter input transformer 1:3 was then needed to be increased to a 1:7 ratio one which naturally drove the grid to a higher music voltage.


Quiescent plate current of the triode connected electron tube is about 8.5mA.


So plate dissipation must be of the order of 600mW. Power out of the order of 200mW.


Sound is nice, smooth, natural, extended in frequency range including bass with both transformers and speakers. The Sowter transformer must be sounding a bit louder and of somewhat wider bandwidth. The Zeiss Ikon speaker sounds about double in loudness with more bass and treble. The Pleiades linoleum Auratone 5C type speaker sounds somewhat more smooth including frequency response perception.


It is certainly possible to have a world class one electron tube amplifier of low power consumption operated with batteries for critical listening at not loud levels, for dinning conversation etc.


Cathode bias must be tried too.





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