Built this circuit up, and caught the need to use a 560 ohm resistor to feed the transistor that drives the LED.? Using a orange LED and a LDR with 20k dark resistance.? Only on very high signals do I get illumination, and even then no perceived AGC action.? Strangely then when I increase gain control, the LED gets brighter which implies awful poor isolation.? To install this thing I disconnected the wire from the hot (or upper) end of the audio gain control - attached this wire to the AGC circuit input and the output onto this pot.? I connected circuit ground to the ground end of the pot, and biased it from the DC connector.?

Circuit seems to work in the videos but not in my build.? Thought about tweaking parts on the input amplifier stage, but as light doesn't lead to attenuation wondering if my build has 2 flaws.? Anyone around who had success with this?? I am not seeking a robust AGC, but somethng to squash the loudest signals, so I need to use it less.? If this thing worked I would implement an AGC on/off switch.?

73 Curt

Curt this is if it is the circuit VK3zzz has been hawking about is? intended for? VOICE COMPRESSION. nothing to do with agc on line to speaker (though it could be used for same at a pinch)? . It is about a 50 year old circuit ,? just after valves stopped being used.? ?THere are specific voice compression types of cct about .. from PRC .. on a PCB.? They work? Others in the group have used them. I will try to send a PM on details.? They are even mentioned? on the ZL Bitx site ..

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Curt this is if it is the circuit VK3zzz has been hawking about is? intended for? VOICE COMPRESSION. nothing to do with agc on line to speaker (though it could be used for same at a pinch)? . It is about a 50 year old circuit ,? just after valves stopped being used.? ?THere are specific voice compression types of cct about .. from PRC .. on a PCB.? They work? Others in the group have used them. I will try to send a PM on details.? They are even mentioned? on the ZL Bitx site ..

QSL OM Maior

can you provide tips on photo-resistor parameters, type of LED, or anything else I should ask ?? is your AGC installed into a uBITX between the board and the volume control??

I get illumination of the LED - but no useful AGC.?

73 Curt

http://ubitx.net/mod-tx-compression/