I am curious about doing this sidetone mod on a K2 rev B. Elecraft changed the sidetone circuit from serial number 3000 on, and wonder how effective the sidetone mod is on a rev B K2. My K2 is serial # 5093.
The mod is described at http://www.raunvis.hi.is/%7Ematti/TF3MA/sidetone_tf3ma.html >From the schematic diagram it looks like L1 82mH is removed and inserted between U10 pin 7 and C33. A new capacitor is then installed at the old L1 position. From the charts on the mod page it looks like about 1 uF would be about right. My L1 82 mH inductor has a DC resistance of 62 ohms. This is quite different from the 180 ohm version used in the mod. Would a series resistor be desired as Fred indicates in the message below? I have 100 ohm, 120 ohm, and 150 ohm resistors on hand. Where is this resistor installed between U10 pin 7 and the inductor or between the inductor and C33? What type of capacitor would be best suited for this mod? My junk box only has 1 uF 100 V 5% metallized polyester or 2.2 uF 16 V 10% dipped tantalum capacitors. The polyester caps are rather large. A couple of the 2.2s in series would be 1.1 uF. Comments and recommendations? Darrell VA7TO K2#5093 On November 15, 2006 06:04 am, [EMAIL PROTECTED] wrote: > The sidetone mod by TF3MA was installed in my K2 right after Marti posted > it. I obtained a 47 mh inductor for this mod from Elecraft. The mod > resulted in an improved sidetone, but left room for further improvement, > especially at lower tones. Additionally there was an objectionable > pin-prick sound at the make of the muting that was annoying to hear. > > Recently I decided to revisit this situation. > > I noticed in Marti's write-up that HIS 47 mh inductor had an internal > resistance of 180 ohms. With the K2 apart, I measured the inductor I had > received from Elecraft and sure enough, it had an internal resistance of > only 40 ohms. This would entirely change the frequency response Marti's > peaking high-pass filter. Elecraft is apparently using an 82 mh inductor > in its mod, I obtained that, and found it has an internal resistance of 60 > ohms which would seem to offer less than an ideal result. > > I put a 150 ohm resistor in series with the 47 mh / 40 ohm inductor > originally used when I modified the radio some years ago. Folks, the > difference is DRAMATIC !!! The sidetone is louder, clear, and is that way > across its entire range from 400 to 800 cycles. Not only that, the tone is > so much stronger that the slight pin-prick click from the make of the > muting line is all but completely inaudible in the strength of the sidetone > and no longer objectionable. > > A big thank you to Marti and to W3FPR who both stayed with me through my > frustration trying to make this thing right. For a while they must have > thought my hearing was the main problem because the radio seemed to have > the right modifications in it to sound well. > > Maybe this will be helpful information for others. > > 73, Fred KT5X -- Darrell Bellerive Amateur Radio Stations VA7TO and VE7CLA Grand Forks, British Columbia, Canada _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
