Some electron tubes suitable for space grid potential mic boosters

Even 10μA anode current can sound big, dynamic, detailed. See previous posts.


Variations of the Pleiades V6 circuit (normally giving more than 50-70μA) can be used:





Since the current can be even lower for a very interesting and big sound (see 1H4 operating as mic amplifier at space potential):


http://euroelectron.blogspot.com/2018/07/1h4-with-grid-at-space-potential-mic.html


and should we wish to proceed the space potential or free grid way:


Then no pull up resistor is needed.


But we might need more anode potemtial.


For example 9V to 18V or 48V if we need to exploit phantom potential. By the way the VF14 of the Neumann U47 has about 40V at the plate?


So we would need electron tubes of high heater voltage specs if the same battery is to be used for both heaters and plate. (Always use a fuse in series with a battery or other voltage source for safety).


Some suitable electron tubes may be:


Nuvistor 13CW4. Heater is 12.6V so it would be greatly underheated with 9V. The grid space potential will be less negative by less electron emission velocities in the vicinity of the grid.


UF89. Vari-μ pentode. It can be connected as triode. The screen grid would capture most of the electrons. Heater voltage is 12.6V and current is 100mA. So with a 9V battery current consumption will be less than 100mA.


UCC85. Heater 26V. So 2 9V batteries can be used making a plenty of 18V anode supply potential. If 2 UCC85 double triodes are used then heater voltage can be the 48V protocol phantom? Plenty of anode potential. See the Pleiadss V(-1) UCC85 mic preamplifier in short tailed pair configuration with open or free grids.


12SK7


And last but not least the VF14. It is underheated by Georg Neumann to 35V at the heaters instead of 60V in the Neumann U47 microphone. He had good reasons. See previous posts.



There is also a WE electron tube with heater voltage of 40V?, see previous posts.


See also that the grid potential can increase when anode potemtial is applied.


http://euroelectron.blogspot.com/2018/08/the-grid-space-potential-increases-when.html