Connecting a Shure SM59 microphone to the Pleiades V6 1H4 battery powered front end electron tube amplifier

At your risk.
Take all,safety precautions.
A suitable fuse must always be connected in series with a battery to prevent a fire hazard.


Today's updates:


The Altec 4722 green input transformer is connected.


There is a narrow band hiss.
This possibly comes from the thermal noise of transformer secondary.
Narrow band as the very high (almost infinite?) input impedance of the grid at space potential creates a very high Q (quality factor) thereby a broadband resonance.


When an 0 ohm XLR (short circuit) is connected hiss almost disappears in an impressive way.


When a 200ohm (wire wound resistor) XLR is connected hiss increases a bit indicating the amplifier can read the thermal noise of a 200 Ohm resistance.
This simulates the perfect mic at complete silence.


Then connecting the Shure SM59.
Somewhat higher varying in time hiss indicating ambient acoustic noise higher than mic's equivalent noise.


Very nice smooth and clean sound.
Lower noise figure (higher S/N) than connecting mic directly to Sony TC-D5 PRO.


Signal path:


Bedroom - Shure SM59 - Pleiades V6 1H4 - Sony TC-D5 PRO - Sennheiser HD580



Schematic is as Pleiades V6 but with an anode supply 12V tiny battery in series with fuse.


An advantage of this front end amplifier is it's low power consumption. Just 50mA for heaters and 50μA for anode circuit.


Thank you God. The first time on my palm a portable battery powered low noise electron tube microphone front end amplifier.