Electronic Devices with open signal control electrode

For example the Pleiades Siemens AC151 IV front end LNA (low noise amplifier) is so low noise when bias resistor is disconnected from base that it can descriminate between short circuit and 200 Ohms capacitively coupled to base. Ie it can read the thermal noise of a 200 Ohm resistance. Not so impresively as the Pleiades V6 1H4 open grid but it can do it even without an input transformer. It is very impressive how quiet both amps are at short circtuited input. And how loud they then sound when a dynamic mic is connected. Ambient acoustic noise is so much magnified.