Thanks for the info Jim. I will add this to the Boatanchors Directory... There are several other AM "Cathode Mod" links there too http://www.af4k.com/Boatanchors_Directory/
On 1 Oct 2004 at 21:43, Jim candela wrote: > > Guys, > > I have accumulated a couple of circuits for series cathode modulation. > One is for a 6146 final, and the other for a 807 final, and both use a sweep > tube or two for the cathode modulator. > > Using this technique for QRO AM at 375 watts carrier output will be > pretty > inefficient since the modulator tube will likely be class A. It could be > class D or E switch mode with a good Low pass filter. I believe that some > early KA1SI PDM rigs used some big tubes this way. As for the filament > transformer, a high standoff is really no big deal so long as you wind it > yourself and insulate accordingly. Heck I once made a 208 VAC to 60 VCT at > 200 amps where I needed 120 KV insulation primary to secondary. Layers of > Mylar sheet (like shingles) and transformer oil did the trick. Could also > maybe use a ferrite horizontal fly back transformer (custom wound) for the > filament. Why use 60 hertz? Could be 50 Khz so long as the filament is at > the right temperature. > > Here is a link to two different cathode modulated AM rigs: > > http://pages.prodigy.net/jcandela/Modulator/ > > > Regards, > Jim > WD5JKO > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Brett gazdzinski > Sent: Friday, October 01, 2004 7:42 AM > To: 'Discussion of AM Radio' > Subject: RE: [AMRadio] Home brew AM > > > Clay, > Sounds like a cool idea, and I always thought it should work well > since there is no mod iron. > > I would go for a lower output using lower voltage though, with different > tubes. > 4500 volts is a lot to expect a filament transformer to handle, and if it > arcs over, it could be into the 110 ac side! > > The 450th is a big triode, so I dont think you can run it single ended > pie net output, you would need to do 2 250th tubes in push pull or > something, > but the 450th would do the cathode modulator quite well. > > It would be interesting to look at what available tubes would work > with this type of circuit. > There are some nice modern tubes to play with, 3cx800's and other > big triodes, or, if it could work, tetrodes. > Not sure how cathode modulating a tetrode would work out. > > If you could cathode modulate a pie net output tetrode, that would open > up a lot of possibilities. > Maybe find one that runs a lower voltage but is good for some power... > > Brett > N2DTS > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Clay W7CE > Sent: Thursday, September 30, 2004 12:52 PM > To: Discussion of AM Radio > Subject: Re: [AMRadio] Home brew AM > > > One option that isn't discussed often because it is considered inefficient > at high power is series cathode modulation. This is accomplished by putting > the modulator tube between the RF amplifier tube's cathode and ground. The > only apparent inefficiency is that you run the RF amp at one fourth of it's > Class C CW power rating. I'm currently considering building such a rig > using a 450TH for the RF amp and another 450TH for the modulator. At 4500V, > the 450TH is good for about 1500W out on CW, and with the modulator tube > added will drop to about 375W of carrier. On modulation peaks it will hit > the tubes CW power level of 1500W. The tube will be doing fairly light duty > at this power level since it can handle 1500W CCS output at 4500V, and > should last a very long time as a result. Based on the price and weight of > 450TH's vs. large mod transformers, I think it's a good trade off. In > addition, the fidelity and audio response will be limited primarily by the > audio driver, not the mod transformer. On the negative side, I have to run > the plates at 4500V vs. about 2500V for plate modulation. The filament > transformer for the RF amp will also need to be hi-pot tested to 4500-5000V > (anyone willing to part with a pair of 7.5V, 12A filament transformers that > will work for this?). > > Any thoughts and advice on this approach will be appreciated. > > Clay W7CE > > > ----- Original Message ----- > From: "Brett gazdzinski" <[EMAIL PROTECTED]> > To: "'Discussion of AM Radio'" <[email protected]> > Sent: Thursday, September 30, 2004 9:03 AM > Subject: RE: [AMRadio] Home brew AM > > > That would be hard, but not impossible. > You would need to read up on mod transformer construction, > find something to use as a core, and wind loads of wire on it, > keeping in mind the very high voltages that it would have to withstand. > > You can buy mod transformers, peter dahl makes new ones, ebay, etc. > Old surplus is best, old military rigs, broadcast rigs, old ham > rigs... > > I am using mod transformers that were built by RCA in the 1940's > for some sort of ship board radio for the Dutch navy I have been told. > > Without any mod iron, you would have to go to some sort of > screen modulation with large tubes. > > Brett > N2DTS > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of GGLL > Sent: Wednesday, September 29, 2004 7:55 PM > To: Discussion of AM Radio > Subject: Re: [AMRadio] Home brew AM > > > Hello people, I agree with the nice look and smell of "glass" AM. Few years > ago, I made my CW/AM transmitter, with an 807 plate/screen modulated, 50 > watts > CW, 40 watts AM output. Started with a triode/pentode oscillator/doubler > VFO, > then converted to solid state oscillator/buffer, followed by a tube driver > (6BQ5) and finally the 807 to a pi tank output. > Making my own plate modulated transmitter (200..300 watts out) is a buzzing > idea in my mind since a couple of months. But here the most difficult item > to > get is the modulation transformer, does someone know a method to build it by > > myself?. > > Many thanks in advance > Best regards > Guillermo - LU8EYW. > > Brett gazdzinski escribió: > > Steve, > > What do you need, everything? > > > > Here's a partial list of what you need: > > > > 3 Chassis 17x3x14, > > 3 panels 19x10.25?, > > 3 sets of side supports, > > Power transformer to give 1500 volts at 500 plus ma, > > Choke at 500 plus ma, two is better, swinging for the modulator, > > Rectifiers (I like the k2aw? bricks), > > Modulation transformer, > > Bleeder resistors, > > Big relay and time delay relay for step start if you go that route, > > 4 Tube sockets, > > Filament transformers, > > Killowatt plug in tank coils and its socket and swinging link, > > Push pull grid coils for the bands wanted, > > Push pull grid tuning cap (150 to 200 pf per section, low voltage) > > Modulator grid drive transformer 8 to 10,000 ohms roughly at 20 or more > > watts, > > 2 Neutralizing caps, > > 4 811a tubes, > > Grid leak resistor (big wire wound pot works well), > > Insulated shaft couplings, > > Plate tuning cap, dual 100 pf 5000 volts or better, > > Meters for grid current, mod current, plate voltage, plate current, > > > > A large pile of wire, high voltage wire, screws, nuts, knobs, connector > > strips, line cord, switches, lights, panel bushings,fuse and holder or > > breaker, > > spacers, ceramic standoffs, rf connectors, etc. > > > > I could give you some stuff, and sell you some stuff most likely, and > > MIGHT be able to get you a mod transformer. > > > > Brett > > N2DTS > > > > > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of > [EMAIL PROTECTED] > > Sent: Wednesday, September 29, 2004 9:52 AM > > To: [email protected] > > Subject: [AMRadio] Home brew AM > > > > > > Thanks for the replies. > > > > The 812/811 combo was sorta what I had in mind. > > > > Getting the components shouldn't be too hard if I keep searching. > > > > Let me start here...anyone have any suitable parts? > > > > About the E class...read a few things about it...sounds most > > interesting...but MOSFETS don't have the fragrance of warm vacuum tubes on > a > > chilly winters evening nor the soft orange glow cast through the rig > > perforations onto the shack walls to keep one company...nor the humming > > vibrations of pumped RF being piped to the outside antenna. > > > > 73 > > Steve WA2TAK > ______________________________________________________________ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:[email protected] > > > > ______________________________________________________________ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:[email protected] > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > --- > Incoming mail is certified Virus Free. > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.770 / Virus Database: 517 - Release Date: 9/27/2004 > > --- > Outgoing mail is certified Virus Free. > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.770 / Virus Database: 517 - Release Date: 9/27/2004 > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected]
