This circuit with current up to 100 mA according to the transformer was found in the Radio Electronics magazine of October 1991. The regulation is done directly by the zeners.
This protection circuit for standing waves was found in a manual of high frequency circuits and...
This high input impedance amplifier stage was found in a 1963 documentation. The transistor...
This setting appears multiple times on the site from different sources. This is from a 2000 manual...