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#1
Posted to rec.audio.tubes
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'Twin Triode' AM Transmiter
In article ,
flipper wrote: On Sun, 28 Aug 2011 20:09:47 -0500, John Byrns wrote: In article , John Byrns wrote: I will try to post a schematic of my proposed 12SN7 transmitter circuit later tomorrow. It also occurs to me that the "plate" winding of the oscillator transformer can probably be translated to the cathode circuit without changing the AC equivalent circuit. This would allow the use of a single winding coil with my partial "fix" idea. I will try to post a schematic of this too. I have posted a schematic of my "Twin Triode" AM Transmitter proposal he http://fmamradios.com/TTAMXmtr.gif This version incorporates my "fix" for the grid bias modulation problem and also illustrates the use of a coil with a single tapped winding, the two winding AES (P-C70-OSC) coil is not required for this version. Oh, ok. Well, that's what I called the typical AA5 'cathode-grid' Hartley. Except, of course, there's not a modulator under it in the AA5. Well, we know circuitmaker isn't modeling the other one right so for what it is or not worth circuitmaker says the AM envelope is not symmetrical. The 'upper' envelope is a smaller amplitude than the lower. However, I think that's again due to the strange osc cathode voltage it comes up with and, so, 'not right'. That is a disappointing result, I wonder if the problem is somehow inherent in the morphed circuit, or if I morphed it incorrectly as I didn't draw out the steps as I had planned to and instead morphed it in my head, or is it a problem with the simulator? Did you use the same component values & 12AU7 as in your original "sim", to eliminate double diddling? That circuit wasn't the one I originally planed on posting first, I had intended on posting my preferred "two winding" design first, as it has fewer changes from your circuit. It would be interesting to see what your simulator does with my preferred proposal. There are two steps to my preferred circuit. The first step is to move the lead of C2 that is connected to L1 pin 3 to L1 pin 4 instead, and then scale the inductance of L1, adjust the core in the physical implementation, to maintain the same carrier frequency so that the reactance of C2 at the carrier frequency will remain the unchanged, before running a "sim". The second step, which yields my target design, is to split the tapped coil into two separate windings by disconnecting the grid part of the coil from the center tap at pin 4, along with the end of C2 that had been moved to pin 4 in the first step, and then reconnecting them both to the oscillator cathode, yielding my proposed two winding circuit. -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#2
Posted to rec.audio.tubes
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'Twin Triode' AM Transmiter
In article ,
flipper wrote: On Mon, 29 Aug 2011 20:38:28 -0500, John Byrns wrote: In article , flipper wrote: On Sun, 28 Aug 2011 20:09:47 -0500, John Byrns wrote: In article , John Byrns wrote: I will try to post a schematic of my proposed 12SN7 transmitter circuit later tomorrow. It also occurs to me that the "plate" winding of the oscillator transformer can probably be translated to the cathode circuit without changing the AC equivalent circuit. This would allow the use of a single winding coil with my partial "fix" idea. I will try to post a schematic of this too. I have posted a schematic of my "Twin Triode" AM Transmitter proposal he http://fmamradios.com/TTAMXmtr.gif This version incorporates my "fix" for the grid bias modulation problem and also illustrates the use of a coil with a single tapped winding, the two winding AES (P-C70-OSC) coil is not required for this version. Oh, ok. Well, that's what I called the typical AA5 'cathode-grid' Hartley. Except, of course, there's not a modulator under it in the AA5. Well, we know circuitmaker isn't modeling the other one right so for what it is or not worth circuitmaker says the AM envelope is not symmetrical. The 'upper' envelope is a smaller amplitude than the lower. However, I think that's again due to the strange osc cathode voltage it comes up with and, so, 'not right'. That is a disappointing result, I wonder if the problem is somehow inherent in the morphed circuit, or if I morphed it incorrectly as I didn't draw out the steps as I had planned to and instead morphed it in my head, or is it a problem with the simulator? Did you use the same component values & 12AU7 as in your original "sim", to eliminate double diddling? That circuit wasn't the one I originally planed on posting first, I had intended on posting my preferred "two winding" design first, as it has fewer changes from your circuit. It would be interesting to see what your simulator does with my preferred proposal. There are two steps to my preferred circuit. The first step is to move the lead of C2 that is connected to L1 pin 3 to L1 pin 4 instead, and then scale the inductance of L1, adjust the core in the physical implementation, to maintain the same carrier frequency so that the reactance of C2 at the carrier frequency will remain the unchanged, before running a "sim". The second step, which yields my target design, is to split the tapped coil into two separate windings by disconnecting the grid part of the coil from the center tap at pin 4, along with the end of C2 that had been moved to pin 4 in the first step, and then reconnecting them both to the oscillator cathode, yielding my proposed two winding circuit. Took me a few minutes to decipher those instructions but I figured it out. Good news is it 'works' and the plate signal looks right. Bad news is the plate signal is only 6.8Vrms so there's little RF power from there. More bad news, the 'big endian' coil we get 'mo power' from looks asymmetrical like the other one. Worse actually. It's not only asymmetrical but on deep mod the 'top side' is heavily distorted from what 'looks like' severe slew limiting. Which seems odd since that's what we're supposedly trying to fix. No, the slew rate problem isn't the one I am trying to fix, your scheme of reducing the time constant is the only way anyone has suggested to fix the slew rate problem. The problem I am trying to fix is a slightly different but related problem, which is also "fixed" by reducing the time constant as you have done. The same 'tweaks' work with this one so, by using a 47k series grid limiter, I could get osc cathode to ride down around 122V, which eliminates the 'cathode crunch' up against the plate signal, so I have a sub fraction more semi confidence it might mean something. I left all values the same as mine except for increasing C2 to 180pF to get a similar frequency. OK, that would reduce the capacitive reactance at the carrier frequency, that may or may not be a big deal, it will probably increase the operating Q of the coil considerably, resulting in greater high frequency rolloff. On mine I went back to 47k for R3 and it seems to have brightened things up a smidgen and it dawned on me, Yes, that is part of the effect I noticed working with the "Zenith" circuit. when I was measuring frequency response and getting 'lower amplitude' at 10kHz I was using full mod. So maybe the small signal response does improve and it's slew limiting I was seeing limit the amplitude. Maybe just wishful thinking and I should take it back up to the scope but, for now, I'm listening to it. Could be, I will have to take a few minutes to think about what you are saying here. -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#3
Posted to rec.audio.tubes
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'Twin Triode' AM Transmiter
In article ,
flipper wrote: On Tue, 30 Aug 2011 21:30:00 -0500, John Byrns wrote: In article , flipper wrote: snip when I was measuring frequency response and getting 'lower amplitude' at 10kHz I was using full mod. So maybe the small signal response does improve and it's slew limiting I was seeing limit the amplitude. Maybe just wishful thinking and I should take it back up to the scope but, for now, I'm listening to it. Could be, I will have to take a few minutes to think about what you are saying here. I took 6 days off from thinking about exactly how I will rebuild my AES phono oscillator with a high level series modulation circuit. In addition to my wife's project to reduce what I call domestic entropy, which will probably extend well into 2012, when you are "94", Patrick's number not mine, health issues crop up which demand attention. The most time consuming though was purchasing a new car for my wife, which involved scouring the country for one that was built before, or shortly after, the tsunami in Japan ended the availability of the optional $395.00 paint job she wanted. The tsunami seems to have ended the production of a particular type of metallic flakes that were used in the desired paint. Well, I did some more testing. I started with the intent to put my air variable in and see how it works over the whole AM band and, as suspected, I had to increase C1 to 20pF for it to oscillate on the lower end. My cap is a typical AA5 dual gang with grounded frame so that meant I had to put it on the coil big end only, which meant I had to screw the slug full in. Still, I was able to get around 540 to 1700 and figured the top end would drop when I tacked the antenna back on but, to my surprise, not only did the top end come down but the lower end of the range came up to, say, 650 minimum. That's interesting, do you have any tentative explanation for the low end increasing from 540 kHz to 560 kHz when you connected the antenna, at first glance it doesn't seem to compute? The BIG surprise though was the 10kHz amplitude response I talked about previously. With everything else remaining the same it changes with carrier frequency from rather lousy on the low end to looking pretty decent at the very top, and deep mod slew distortion follows hand in hand. That shouldn't have been a big surprise, when the tuning is done with a variable capacitor the circuit Q increases when tuned to lower frequencies, remember that the grid resistance forms the main load on the oscillator, so the band width becomes narrower at the low end, plus there is a double whammy because not only does the Q increase, but the carrier frequency is lower further narrowing the bandwidth. I don't understand why but it settles the tuning range question. Pick C2 so the range is pushed up to the top end. The "top end" seems to be a better choice anyway because frequency availability is better up there, and if you are going for a fancy matched antenna to maximize range, the antenna is likely to be more efficient at the "top end". -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#4
Posted to rec.audio.tubes
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'Twin Triode' AM Transmiter
On Tue, 06 Sep 2011 21:33:20 -0500, flipper wrote:
It's posted on the web page so see what you think. http://flipperhome.dyndns.org//Twin%...ransmitter.htm Only the photo of the breadboard is showing. And the text - pale blue upon white - is near illegible. d |
#6
Posted to rec.audio.tubes
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'Twin Triode' AM Transmiter
On Wed, 07 Sep 2011 00:25:34 -0500, flipper wrote:
On Wed, 07 Sep 2011 05:23:39 GMT, (Don Pearce) wrote: On Wed, 07 Sep 2011 05:20:46 GMT, (Don Pearce) wrote: On Tue, 06 Sep 2011 21:33:20 -0500, flipper wrote: It's posted on the web page so see what you think. http://flipperhome.dyndns.org//Twin%...ransmitter.htm Only the photo of the breadboard is showing. And the text - pale blue upon white - is near illegible. d OK, a second try at loading the page sorted it. d Ok, good. I've also noticed some odd Internet behavior but don't know if it's my end or the ISP (it's usually not my end). I notice the site is directed through dyndns. Is it on your own home PC or does the ISP host it? d |
#7
Posted to rec.audio.tubes
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'Twin Triode' AM Transmiter
On Wed, 07 Sep 2011 01:05:34 -0500, flipper wrote:
On Wed, 07 Sep 2011 05:40:19 GMT, (Don Pearce) wrote: On Wed, 07 Sep 2011 00:25:34 -0500, flipper wrote: On Wed, 07 Sep 2011 05:23:39 GMT, (Don Pearce) wrote: On Wed, 07 Sep 2011 05:20:46 GMT, (Don Pearce) wrote: On Tue, 06 Sep 2011 21:33:20 -0500, flipper wrote: It's posted on the web page so see what you think. http://flipperhome.dyndns.org//Twin%...ransmitter.htm Only the photo of the breadboard is showing. And the text - pale blue upon white - is near illegible. d OK, a second try at loading the page sorted it. d Ok, good. I've also noticed some odd Internet behavior but don't know if it's my end or the ISP (it's usually not my end). I notice the site is directed through dyndns. Is it on your own home PC or does the ISP host it? d It's here at home on a old P133 notebook running Windows98SE. The web server is Savant. That's all it does. Local LAN access is zippity do da fine. I think the problem is the dynamic dns server. It probably needs reminding who you are from time to time. The web site would work much better if you hosted it your ISP. d |
#8
Posted to rec.audio.tubes
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'Twin Triode' AM Transmiter
In article ,
(Don Pearce) wrote: On Wed, 07 Sep 2011 01:05:34 -0500, flipper wrote: On Wed, 07 Sep 2011 05:40:19 GMT, (Don Pearce) wrote: On Wed, 07 Sep 2011 00:25:34 -0500, flipper wrote: On Wed, 07 Sep 2011 05:23:39 GMT, (Don Pearce) wrote: On Wed, 07 Sep 2011 05:20:46 GMT, (Don Pearce) wrote: On Tue, 06 Sep 2011 21:33:20 -0500, flipper wrote: It's posted on the web page so see what you think. http://flipperhome.dyndns.org//Twin%...ransmitter.htm Only the photo of the breadboard is showing. And the text - pale blue upon white - is near illegible. d OK, a second try at loading the page sorted it. d Ok, good. I've also noticed some odd Internet behavior but don't know if it's my end or the ISP (it's usually not my end). I notice the site is directed through dyndns. Is it on your own home PC or does the ISP host it? d It's here at home on a old P133 notebook running Windows98SE. The web server is Savant. That's all it does. Local LAN access is zippity do da fine. I think the problem is the dynamic dns server. It probably needs reminding who you are from time to time. The web site would work much better if you hosted it your ISP. However it would be lacking in cool factor if hosted at the "ISP". -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#9
Posted to rec.audio.tubes
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'Twin Triode' AM Transmiter
In article ,
flipper wrote: On Sun, 04 Sep 2011 20:25:25 -0500, flipper wrote: snip Some sort of modulation meter would be more useful but neither easy nor particularly inexpensive, compared to the rest of it. Well, I kludged up a simple 'modulation indicator' in spice, but I haven't actually built it. It's posted on the web page so see what you think. http://flipperhome.dyndns.org//Twin%...ransmitter.htm The commonly obvious thing would be to make a 'LED VU' meter with something like the LM3915 but the modulator drive has an interesting problem in that trying to sense 'max' positive mod may not be so simple due to positive grid drive potentially clipping the signal. It shouldn't if everything is 'right', but it might not be, and then there's the matter of 'calibrating' the thing even if all else is okay. Positive mod isn't the 'real' (or biggest) problem anyway, it's carrier cutoff on negative mod, and 0 modulator current has the advantage of being 0 no matter what 'idle' or peak positive mod is. So I look for modulator cathode approaching 0, rather than worry about 'calibrating' to positive mod, then peak hold/decay it for visual. (Note, the LM3915 doesn't peak hold so you could easily miss seeing carrier cutoff events even if you got it calibrated right) The yellow 'mod' LEDs are for visual effect. The R15/C19 filter senses 'idle current' and U1B, then, generates (rectified half sine) pulses proportional to positive mod to drive the LEDs. We don't care if it's terribly accurate as it's sort of like those 'musical lights' things where light intensity dances around to the music. The idea is a sort of 'glow indicator'. Like, maybe, aiming the LEDs into a diffuser, or not. I haven't worked out the details. Probably need to buy some 'wide angle' flat LEDs and see just how well they disperse and how it looks. In theory it would be nice to know our peaks are -3dB, or whatever, but for something this simple I think people would slam it as high as they can anyway, so a red 'too much' indicator is probably sufficient, and calibration, as mentioned, would be non trivial so it's unlikely -3dB would have much meaning to the actual problem. At least that was my thinking: a modulation 'idiot light', to use a car analogy. A simple tripler off the heater supply should be enough to power it. It's an interesting coincidence that you are working on this idea, as I have been thinking along similar lines the past couple of days. As you allude to above, I think the important thing would be to monitor the onset of oscillator dropout and flash warning indicator at that point. The idea that struck me was to use a neon bulb like some 1950s era tape recorders used as recording level indicators. To a first approximation a neon bulb and two resistors would do the job. One connection of the neon bulb would be go to the modulator plate, with the second connection to the junction of two resistors forming a voltage divider between B+ and ground. The potential at the junction of the two resistors would set the firing voltage for the neon bulb, and the fact that the firing voltage is higher than the conduction voltage would provide a sort of faux peak hold effect. Calibration of this circuit should be easy as we only have to identify the point where the oscillator drops out, not the precise point of 100% modulation. There is at least one obvious problem with this elegantly simple scheme, which is that when the neon bulb fires it would drag the modulator plate down to a lower voltage, creating serious distortion. This problem could be overcome at the cost of an additional triode operating as a cathode follower to drive the neon bulb, buffering the modulator plate. Unfortunately besides requiring the extra triode, an additional higher voltage power supply would be required for the cathode follower plate, to prevent it from saturating before the point where the oscillator drops out. Most old vacuum tube era professional AM broadcast modulation monitors required calibration vs. an external source such as Patrick's trapezoidal CRO display. There was one old modulation monitor though which was self calibrating, that was the Gates M5693 Modulation Monitor. The ideas from this monitor should be easy to adapt to the modern solid state opamp era. A year ago I worked out a scheme to implement this self calibrating idea in a single quad opamp to drive an analog peak modulation meter. A little additional circuitry, as in the actual MS5693, could provide for driving a red peak flasher LED, and the analog meter could be replaced with an orange LED "VU" meter. An AM demodulator would be required to drive this circuit, the oscillator plate, which is a lower impedance point than the grid circuit where the antenna is connected, might provide enough RF drive voltage for a demodulator diode without unduly loading the oscillator circuit. If you want to puzzle out the self-calibrating principle used in the M5693, the operating instruction manual and schematic can found here. http://louise.hallikainen.org/~harol...GatesM5693.pdf -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#10
Posted to rec.audio.tubes
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'Twin Triode' AM Transmiter
On Wed, 07 Sep 2011 15:47:48 -0500, flipper wrote:
On Wed, 07 Sep 2011 15:45:35 GMT, (Don Pearce) wrote: On Wed, 07 Sep 2011 01:05:34 -0500, flipper wrote: On Wed, 07 Sep 2011 05:40:19 GMT, (Don Pearce) wrote: On Wed, 07 Sep 2011 00:25:34 -0500, flipper wrote: On Wed, 07 Sep 2011 05:23:39 GMT, (Don Pearce) wrote: On Wed, 07 Sep 2011 05:20:46 GMT, (Don Pearce) wrote: On Tue, 06 Sep 2011 21:33:20 -0500, flipper wrote: It's posted on the web page so see what you think. http://flipperhome.dyndns.org//Twin%...ransmitter.htm Only the photo of the breadboard is showing. And the text - pale blue upon white - is near illegible. d OK, a second try at loading the page sorted it. d Ok, good. I've also noticed some odd Internet behavior but don't know if it's my end or the ISP (it's usually not my end). I notice the site is directed through dyndns. Is it on your own home PC or does the ISP host it? d It's here at home on a old P133 notebook running Windows98SE. The web server is Savant. That's all it does. Local LAN access is zippity do da fine. I think the problem is the dynamic dns server. That wouldn't explain the recent 'in general' odd Internet behavior I'm seeing since none of that is dyndns related. It probably needs reminding who you are from time to time. I have a semi static IP. I haven't ever seen it change 'on it's own', it's just not 'guaranteed'. It will have an assigned lifetime and will expire if you don't log in for some time. That time is probably upwards of a week. The web site would work much better if you hosted it your ISP. d I prefer the control and it being ISP 'independent'. Hardly ISP-independent. Your IP address still comes from the block assigned to your current ISP. d |
#11
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'Twin Triode' AM Transmiter
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