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ms660 · 14th Nov 2017, 9:15 pm

Yes, no cathode resistor, the AGC delay operating voltage is taken from the HT via a 20Meg resistor to the anode of one of the diodes in the EBF80, the diode conducts due to that feed and reduces the AGC voltage to a minimum on weaker signals, stronger signals cause the diode to cut off, thus increasing the AGC voltage.

With the HT feed resistor to the AGC delay diode having such a high resistance it probably wouldn't need much leakage from any +ve voltage source to the diodes anode to send the AGC voltage to zero or +ve on weak signals, due to the circuit impedances that might be difficult to measure unless the pot. divider and battery trick is used.

Just dreamin'

Lawrence.

14th Nov 2017, 9:15 pm	#70
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Oh No! Not another howler. Yes, no cathode resistor, the AGC delay operating voltage is taken from the HT via a 20Meg resistor to the anode of one of the diodes in the EBF80, the diode conducts due to that feed and reduces the AGC voltage to a minimum on weaker signals, stronger signals cause the diode to cut off, thus increasing the AGC voltage. With the HT feed resistor to the AGC delay diode having such a high resistance it probably wouldn't need much leakage from any +ve voltage source to the diodes anode to send the AGC voltage to zero or +ve on weak signals, due to the circuit impedances that might be difficult to measure unless the pot. divider and battery trick is used. Just dreamin' Lawrence.