It applies especially if the noisy area is near full counter-clockwise rotation (minimum gain) and it's an old K2 that was never modified.
In the original design, the K2's audio gain pot acted as a shunt across the audio line. As you rotated it counter-clockwise (CCW) it literally "shorted" out the audio, reducing the speaker/phones output. That worked fine, but it also resulted in many K2's being operated near full CCW. As it happens most pots tend to be noisier near minimum resistance so normal pot wear caused them to sound "scratchy" in a fairly short time. The mod alters the circuit to use the pot in a more normal way. It has two advantages: 1) The pot is seldom (if ever) used in the near-minimum area where it tends to be scratchy and 2) the action of the pot is more nearly logarithmic, producing the sort of change in gain as the pot is rotated we normally see in audio gain controls. Ron AC7AC -----Original Message----- Does this app note apply here? Application Note: Alternative Wiring for the K2's AF GAIN Control Wayne Burdick, N6KR, with illustrations by Tom Hammond, N0SS Oct. 25, 2001 This optional modification greatly reduces the level of noise or other artifacts that might be heard on a small number of K2s when rotating the AF GAIN potentiometer. Pots judged as "noisy" are, in fact, probably good; the original circuit is simply sensitive to the pots' inherent non-linearities. In addition to eliminating most pot noise, the new circuit provides nearly dead silence when the control is fully CCW, while the old circuit allowed a small amount of leak-through. You can find the whole note in K2/K1 applications. ---- Original message ---- > >I just noticed my K2 has a problem with the AF Gain control. It >is "scratchy" in the area where I use it most. I see that the RIT control >(rarely used) also has some linearity issues. The rig is about three years >old. I do not use it on a daily basis, but I do use it in contests , where >it gets stressed pretty well. > >I must either clean or replace the AF Gain control ASAP, and I see it will >be rather hard to get at. Can anyone tell me if these controls can be >accessed to clean them, or should I just order replacement parts? It would >help to know before I tear the rig apart. > >Thanks and 73, > >Tom, KG3V ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
