Hi Joe There's certainly more than one way to deal with this. External buffer chips are an inexpensive solution. I didn't want yet another piece of clutter in my already box and cable littered shack so I chose to mod the K3.
The K3 driver chips are not an issue at all. Any additional external pullup would add to their load but would also provide the desired additional pullup drive and make it possible to increase the value from 820ohms to perhaps 1K. The KAT500/KPA500 add a fraction of a milliamp in total so they are not an issue. They are the only devices other than the RCS12 on the band outputs in my case. The only other consideration is that the increased internal pullup drive (lowered resistance) puts more load on the 5v regulator sourcing current to those pullups. Again not an issue. 73 jim ab3cv On Sun, Dec 2, 2012 at 9:41 AM, Joe Subich, W4TV <li...@subich.com> wrote: > I would be careful when decreasing the value of the pull-up resistors > in the K3. The "Band Data" outputs are open drain - decreasing the > pull-ups increases the current the outputs must sink at logic low on > top of any current sourced by the external devices. It might be better > to buffer the RCS12 using something like the 74ACT244 (at less than > $0.25) to drive the 2N3904s. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
