This circuit was found in a 73 magazine for radio amateurs of the 90s. The circuit uses two types of indicators, the diodes are for general use. The power supply is 5 V.
This General Electric circuit is from the 80's. The PUTs used in this meter are not common...
This circuit uses a transistor as noise source and a 741 IC as amplifier, sourcing a high...
In the figure we have a practical circuit for a 50 kHz bandwidth amplifier using a photo diode as...