Hi Herb, I'd have to open up my L75 to be sure, but I believe all I did was etch away some of the copper around the outside edge of the board (to prevent arcing around the edge of the board) and then sprayed it with Q-dope to prevent arcing to the air (corona discharge) from the edges of the copper.
It is also very important to use low-loss PC board material. When I tried it with standard FR4 PC board material, the capacitor started to smoke after a few seconds with a couple hundred watts of RF. We used glass-teflon PC board, but other low-loss material like Duroid might also work. http://www.rogerscorp.com Alan On Fri, 2010-11-12 at 15:39 -0400, Herb Schoenbohm wrote: > > > I was working on at the time. For example, the MN2700 kilowatt antenna > > tuner required some high-voltage, high-current fixed capacitors. We > > were quoted a ridiculously high price and a 6-month lead time by the > > vendor. So we figured out a way to make our own capacitors from Teflon > > printed circuit board (for low loss / high Q) spray-painted with Q dope > > to prevent corona discharge. > > > > > > Alan N1AL > > > > Alan, That component design of Milt was also was used in the Drake > > L-7 amp. I lost that cap several years ago in both the amp and the > > add on ones in the MN2700. For the amp a I found a door knob with > > enough current and voltage to work. But for the tuner there just is > > not enough space to mount the replacements fixed caps. Do you know of > > anyone who makes these flat board PC caps? Or could someone make a > > sandwitch out of some doble side copper PC board. I think, however > > the edges would be a voltage breakdown problem and Milt's unique > > design had an island of insulation around the edges plus the Q dope. > > Thanks, > > Herb Schoenbohm, KV4FZ ______________________________________________________________ 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
