No. The KT88's are AB1 so a phaze inverter does the job. A long time ago I gave the driver transformer away, as I had a bunch of 32V's.
The mike is a D104, it goes into a 6SL7, the filaments run off DC, the 2nd stage of the 6SL7 is a voltage amp, then into the 6SN7 phase splitter circuit. I have the phase splitter circuit unbalanced a bit to give more positive modulation. The feedback circuit acts a bit like a tone control, less feedback gives a brighter sound. It sounds ok for a D104, and I get plenty of audio on the carrier. I had to re-do the screen supply for the 4D32, and take some modulated and unmodulated voltage to feed it. Brett > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of John > Coleman ARS WA5BXO > Sent: Sunday, March 26, 2006 10:02 PM > To: 'Discussion of AM Radio' > Subject: RE: [AMRadio] Modulator design needed > > Are you using the stock driver circuit with the driver XFMR > on the 32V3? > > John, > WA5BXO > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Brett gazdzinski > Sent: Sunday, March 26, 2006 8:42 PM > To: 'Discussion of AM Radio' > Subject: RE: [AMRadio] Modulator design needed > > I have KT88's as modulators in my 32V3, regulated screens > (VR tubes), and don't have any problems. > I have feedback from the sec of the mod transformer to a stage > before the phase splitter, and had to chop off the high frequencies > because of the phase shift in the mod iron. > > I don't have any fancy bypass stuff, and no instability up to > 800 volts on them. > > I always thought if you were going to amplify audio, you should > try to use low distortion tubes made for audio if you could. > > I like triodes, or AB1 using low distortion tubes. > > Brett > N2DTS > > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of John > > Coleman ARS WA5BXO > > Sent: Sunday, March 26, 2006 9:03 PM > > To: 'Discussion of AM Radio' > > Subject: RE: [AMRadio] Modulator design needed > > > > I haven't actually built much in the way of audio with 6146 however > > OTIS, K5SWK, has done a lot with the tube I am sure it was > > all standard > > tetrode connections. He contends that the screen supply needs to be > > well regulated and the control grid leak resistor, if AB1, > needs to be > > kept low, in the 100K or less region. He says that the circuits are > > prone to RF oscillation and need carbon resistors in series with the > > control grid and plates. I've seen him attach a wire to a plate and > > play with low capacitance gimmick feed back to and opposite > > grid. It's > > sort of neutralizing, although sometimes, depending on the circuit > > layout, the gimmick needs to come back to its on grid. It's > > a trial and > > error thing. I think keeping the grid resistors low helps > in this as > > well. At any rate he has built some awesome sounding > amplifiers with > > 6146s at 600V and up where stability is really important. > > > > I am currently assembling a 50 watt per channel KT88 amp. Two per > > channel with a 5000 ohm plate load XFMR. Plate supply is > 450V and the > > regulated screen supply at 320 volts. Standard tetrode > > connection. Also > > am using a little inverse feed back from the 16 ohm out back to the > > cathode resistor of the triode before the phase splitter. > I'm having > > some stability trouble with or with out the feedback. At high input > > levels I was getting a HF parasitic burp and I am currently > > trying some > > of Otis's tricks. I think I've about got it settled down. I think > > bypassing the screens and filaments with .01 ceramics has > > made the most > > deference. I'd found in the past that the filament lines can be the > > transport path for RF parasitic oscillations and that electrolytic > > capacitors don't bypass HF very good. > > > > John, WA5BXO > > > > > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of Brett > gazdzinski > > Sent: Sunday, March 26, 2006 7:09 PM > > To: 'Mike Dorworth, K4XM'; 'Discussion of AM Radio' > > Subject: RE: [AMRadio] Modulator design needed > > > > I never had much luck getting 6146's sounding good as modulators, > > I think it takes a fair amount of effort. > > > > > > The KT88 or KT90 on the other hand works great in AB1. > > > > The KT90 is reasonable in price, and can run up to 800 > volts or more, > > 170 watts out I think in AB1 at low distortion. > > > > Brett > > N2DTS > > > > > > > > > > > -----Original Message----- > > > From: [EMAIL PROTECTED] > > > [mailto:[EMAIL PROTECTED] On Behalf Of Mike > > > Dorworth, K4XM > > > Sent: Sunday, March 26, 2006 5:05 PM > > > To: Discussion of AM Radio > > > Subject: Re: [AMRadio] Modulator design needed > > > > > > 6146.... AB-1, 500 volts, 75 watts, 600 Volts, 95 watts, 750 > > > Volts, 120 > > > watts.. > > > > > > I thought the original question was to modulate a Johnson 6N2 > > > which uses a > > > 5894. Usually one uses the same Plate supply for the final as > > > the modulator. > > > The 6146 gives way too much power for the voltage rating the > > > 6N2 would use, > > > 450-600 Volts. The AB-1 807 or some of the hotter 6L6 > > > versions such as 6L6GC > > > seem more in the same voltage line to give the power needed. > > > > > > The Viking II could do the whole job with a Ceramic 4 pole, > > 2 position > > > switch as shown in Bill Orr's 14 Edition Handbook (his First) > > > It was mounted > > > on the rear apron along with a 3 lug terminal strip. > > > > > > In the older 12th Edition (Editors and Engineers) there is > > > shown a phase > > > inverter driving 6V6's and also one driving pair 813. A 6C4 > > > in the former > > > and a pair of 6SJ7's in the later case. On the AM Forum > > > Archives there is a > > > pair of 4-400's driven in AB-1 by a pair of 2E26. Google > > > N9FOY and click on > > > modulator. Circuits from 6AQ5, 6V6, 807, 6146, 813, 4-400 all > > > published and > > > none using driver transformers shows this is an OK way to go > > > for most any > > > power level. > > > > > > Mike > > > > > > ______________________________________________________________ > > > AMRadio mailing list > > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > > Help: http://mailman.qth.net/mmfaq.html > > > Post: mailto:[email protected] > > > AMfone Website: http://www.amfone.net > > > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > > > > > > > ______________________________________________________________ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:[email protected] > > AMfone Website: http://www.amfone.net > > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > > > > > > > > ______________________________________________________________ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:[email protected] > > AMfone Website: http://www.amfone.net > > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb >
