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Title: Neutralizing Cap Post by: K9ACT on October 21, 2007, 02:06:58 PM Going to two tubes on my 8000 means that the neut cap has to be twice the value.
According to the handbook, I need a spacing of .250" for 1600 VDC AM. Using the cap that I made for the single tube requires a spacing of about .1" to get to the needed value (about 17 pF). This can be seen in the pic attached and to get there with this design, I have to make another one about 5" in diameter. This would be a rather big klunky beast and it seems like there should be a better way. The bias supply has been moved under the chasis and the new tube is where that was in the pic. What do people use for N/C's for this application? js p.s. I don't have much luck attaching pics to these messages so if it's not here, go to http://schmidling.com/rfd4.jpg js Title: Re: Neutralizing Cap Post by: KB2WIG on October 21, 2007, 02:44:07 PM some use a treaded rod placed near the tube(s) to be nutered; use a ceramic feed through insulator and raise the rod up/down to change the capacitance.... or so i'm told... Thats what i'm gunna do with my 813/810 maul... klc
Title: Re: Neutralizing Cap Post by: K9ACT on October 22, 2007, 12:16:44 AM some use a treaded rod placed near the tube(s) to be nutered; use a ceramic feed through insulator and raise the rod up/down to change the capacitance.... or so i'm told... Thats what i'm gunna do with my 813/810 maul... klc Not sure I can picture that but it sounds more like a "gimmick" cap for a tetrode. You need a serious cap for big triodes, especially in parallel. In my case, about 16 puff. js Title: Re: Neutralizing Cap Post by: KB2WIG on October 22, 2007, 12:29:54 AM yes, ur right........... I'M doing a PP 813 driven by PP 810 mudulators ... the brain (if its still in there) got it backwards. Anyway good luck, gud night ............ klc
Title: Re: Neutralizing Cap Post by: WD8BIL on October 22, 2007, 09:32:26 AM Hi Jack....... are these tubes in PP or parallel ?
Tom's parallel 813 rig uses a nifty neuter setup. Check it out here. 813s X 813s (http://www.amwindow.org/tech/htm/813/813print.htm) Title: Re: Neutralizing Cap Post by: K9ACT on October 22, 2007, 12:29:41 PM Hi Jack....... are these tubes in PP or parallel ? Tom's parallel 813 rig uses a nifty neuter setup. Check it out here. 813s X 813s (http://www.amwindow.org/tech/htm/813/813print.htm) Again, that is for tetrodes that are not supposed to need neutralizing in the first place. I do not understand quite how it works anyway. I solved the problem in a way that I do understand. By coincidence, (Mack) I picked up two small NC's at the last hamfest, only because of all the work it took to make mine. They are two small to do anything with but I was able to disassemble them and put it back together on one mount in parallel. They are now about 6 pF with .25" spacing. This in parallel with the original at .25" gives me just what I need. A bit Rube'ish but it works. Pic attached.... Gonna fire it up after my coffee. js Title: Re: Neutralizing Cap Post by: WA1HZK on October 27, 2007, 05:04:10 PM Big Triodes, Big cap. I ended up with around 10 pf. on a trimmer that had the same spacing as the final plate tuning cap in my 833 rig. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Keith WA1HZK |