UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Interesting Armstrong AM detector circuit.

G8HQP Dave · 31st Oct 2017, 2:35 pm

The negative peak problem can be reduced (possibly eliminated) by adding some extra current to drag the capacitor down, as you say. This current can also serve to pull a semiconductor diode onto its knee at around 0.6V, yet some designs achieve this by sending the current into the 'input' side of the diode - thus making the negative peak problem worse instead of better! A thermionic diode has the opposite problem: it starts conducting just below forward voltage so this trick does not work.

31st Oct 2017, 2:35 pm	#23
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Interesting Armstrong AM detector circuit. The negative peak problem can be reduced (possibly eliminated) by adding some extra current to drag the capacitor down, as you say. This current can also serve to pull a semiconductor diode onto its knee at around 0.6V, yet some designs achieve this by sending the current into the 'input' side of the diode - thus making the negative peak problem worse instead of better! A thermionic diode has the opposite problem: it starts conducting just below forward voltage so this trick does not work.