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Title: SX-111 AVC RESPONSE Post by: k7mdo on August 25, 2016, 11:57:20 PM I'm working through a rebuild of a Hallicrafters SX-111 which is now operational but exhibits a very fast AVC response.
I would like to damp it a little and looking at the circuit it seems like just adding a capacitor to ground might be all that is needed. Anyone have experience with such a modification? The circuit takes some voltage from a detector and routes it back to the grids of the first two tubes. I'm going to try some capacitor values but thought there might be some other more sophisticated approach!? 73, Tom Title: Re: SX-111 AVC RESPONSE Post by: w4bfs on August 29, 2016, 01:59:02 PM took a fast look at skizmatic .... 6bj7 diode to grn, series 1 meg resistor, C26 - .047 uFd cap to gnd gives as I see a 47 millisec time constant ....a bit fast maybe try adding a .1 ufd in parallel .... watch for attack distortion increase
Title: Re: SX-111 AVC RESPONSE Post by: k7mdo on August 30, 2016, 01:28:04 AM That confirms my thinking too and I will "creep up" on increased capacitance and let you know how it turns out. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Just by chance I have both an early -111 without a product detector as well as a -111 Mark 1 with product detector. They both seem a little fast in general listening response... Interestingly the early -111 is the most pleasant to listen to AM stations. They are sideband receivers but with a relatively wide bandwidth. 73, Tom |