Electron tube power amplifier with grid at space potential

At your own risk. Use all safety precautions. Including hearing protection.


After reading patent US3729588, Inventor Berland O, Applicant: American Danish Oticon and the beautiful simple single ended class A schematic that has the speaker as the collector load itself...


https://worldwide.espacenet.com/publicationDetails/biblio?DB=EPODOC&II=2&ND=3&adjacent=true&locale=en_EP&FT=D&date=19730424&CC=US&NR=3729588A&KC=A


And then drawing on the sand 2 schematics:


The Pleiades 2N3053 one transistor power amplifier and


The Pleiades V6 mic booster with grid open or at space potential...


The following question follows logically:


If open or floating grid gives a big and unstressed sound as a mic booster....


Then how would an electron tube power amplifier sound with open grid or gird at space potential?


A grid is more negative to cathode as the cathode is positive by missing emmited electrons.


So we may connect a high Z headphone (attention to hearing), a high Z speaker, or an output transformer to anode and then increase anode potential until the anode current required is obtained.


Even with 21V at plate the EF183 gives about 0.5mA anode current, see previous post.


High anode voltages make ionization or secondary emmision and the grid may be affected.


Relative low anode potential may create a field that penetrates the grid area. This reduces the negative space potential of the grid.


So perhaps 12-24V should be great for a headphone power amp and 50V for example great for driving a loudspeaker at top quality.


If more sensitivity is needed an input trasformer could be used coupled by capacitor. Or if an external potential can be created equal to grid space potemtial then the capacitor could be omitted?


A top quality speaker can be the Philips high Z AD5046N, see Pleiades 2N3053.



Interesting tubes: 12AU7, EF183 triode connected, 12SK7 triode connected, 6A3 or 2A3, UL84, ECL82, PCL86, 6L6, JAN CRC 1619

Obviously the very small electron tubes and at very low plate potemtial for headphone direct driving and taking as safety hearing protection measures.


Further reading:


Open grid tubes in low level amplifiers - Robert J. Meyer - Electronics


Pleiades V6 schematic but with anode to grid pull up or Pleiades bias resistor removed. the open grid potential would be more negative due to positive cathode missing electrons to the cloud.