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Re: A three Phase question please
John Woodgate
In message <l9afub+10tlbe4@...>, dated Mon, 23 Dec 2013,
sawreyrw@... writes: The 2 wattmeter method will work, but to avoid building a model of theThe OP asked how to do it in real life, and that is what I posted. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Nondum ex silvis sumus John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK |
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Re: JFET Model
John Woodgate
In message
<CANnsUMHruA-cbtCW3yswZaaKDayat7KKSm1wdPE3YZpvtmrAww@...>, dated Mon, 23 Dec 2013, Chris Maness <chris@...> writes: So would the change in gain due the change in B+ be the most likelyOne way to tell is to analyse the circuit in detail, or you could try to find Clapp's original paper: J. K. Clapp, "An inductance-capacitance oscillator of unusual frequency stability", Proc. IRE, vol. 367, pp. 356-358, Mar. 1948. For analysis, look at the size of the a-g1 capacitance compared with the tuning capacitor (the 'capacitance tap' capacitors should be so much larger that their effect is negligible). The consider what internal gain would be needed for a small change in the Cag to affect the frequency by say 1 kHz. If that turns out to give a gain of 10 000, you can be pretty sure that you don't have a Miller effect problem. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Nondum ex silvis sumus John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK |
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Re: A three Phase question please
John, The 2 wattmeter method will work, but to avoid building a model of the wattmeters, it?would easier?to simply use the LTspice power plotting feature.? You can easily get a numerical display of the power.? To get total power you need to add the power in each phase. Rick |
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Re: JFET Model
So would the change in gain due the change in B+ be the most likely cause of f_o change for a Clapp oscillator with a valve state amplifier?? The reason for the inquiry is at this point mostly academic.? I love learning things as I work my way through fixing an old radio.? If indeed that is the case, then it would be the Miller effect indirectly. Thanks, On Dec 23, 2013 2:29 PM, "John Woodgate" <jmw@...> wrote: In message |
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Re: JFET Model
John Woodgate
In message <CANnsUMFiEqEOs9Si0pke8F-9R34KDT+DGL8kOgkA3oN15_WQ-g@...>, dated Mon, 23 Dec 2013, Chris Maness <chris@...> writes:
A friend of mind sites the miller effect as being the reason for f_o shift. I will have to read up to see if this is indeed the case.Miller effect is feedback via the anode-to-control grid capacitance. It can depend on B+ voltage if the stage gain changes with B+ voltage. I doubt that it does very much in a JFET, operating in 'FET saturation' (pentode region), which is not the same as bipolar 'saturation' (bottomed). And the drain-gate capacitance is much smaller anyway than in some tubes (you need to take external strays into account because of the physical size difference). -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Nondum ex silvis sumus John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK |
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Re: JFET Model
In this case, "Miller Effect" capacitance is just the gate-drain capacitance multiplied by the stage gain. Miller capacitance won't change unless one or the other (gain, or Cdg) changes. Cdg WILL change with drain voltage. I am not sure, but it is pretty likely that the JFET spice model does not include the voltage dependency of Cdg. If so, this is NOT unique failing of LTspice because all of the spice simulators tend to share model definitions. Jim Wagner Oregon Research Electronics From: "Chris Maness" To: LTspice@... Sent: Monday, December 23, 2013 1:25:54 PM Subject: Re: [LTspice] RE: JFET Model The frequency does change in real life. I am working with the design |
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Re: JFET Model
The frequency does change in real life. I am working with the design
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limits of late 1950's technology. The radio in question uses an OA2 for a shunt regulator. I thought of replacing it with a high voltage zener, but they can't handle 15mA of shunt current. They also probably have even worse regulating properties than the venerable OA2 Argon discharge tube. A friend of mind sites the miller effect as being the reason for f_o shift. I will have to read up to see if this is indeed the case. Regards, Chris KQ6UP On Mon, Dec 23, 2013 at 1:08 PM, John Woodgate <jmw@...> wrote:
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Re: JFET Model
John Woodgate
In message
<CANnsUMFQLY+eCBVz8ow+K+HLOREL12FBwcBXhgVO-DuQqOAfzQ@...>, dated Mon, 23 Dec 2013, Chris Maness <chris@...> writes: .? I was trying to see how changing voltage changes the resonantIt ought not to in real life, of course. If it does, it's due to some second or third order effect in the tube, such as a change in effective inter-electrode capacitance. Your tube had 4 or 5 electrodes, too, whereas the JFET has only 3 (or you could say just 2, because drain and source are interchangeable). I guess spice doesn't model that though. Changing B+ has no effect onThe same sort of effect on capacitances might occur in a JFET, and the model might or might not include that. If it includes it, then LTspice will, of course, take it into account. BUT the effect would probably be much smaller that for a tube, so the frequency shift would be correspondingly smaller. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Nondum ex silvis sumus John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK |
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Re: JFET Model
Thanks, Tony.? I actually got the Clapp oscillator working with a JFET substituted as a the vacuum tube.? I didn't really even need to change the schematic.? I just lowered B+ from 150V to 12V.? Obviously the JFET does not need screen grid bias, so I just left that part out.? I was trying to see how changing voltage changes the resonant frequency.? I guess spice doesn't model that though. Changing B+ has no effect on freq in spice. Regards, On Dec 23, 2013 12:05 PM, <tony@...> wrote:
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Re: JFET Model
Hello Chris, I don't know what you expect to learn from substituting a JFET for the tube, but why not try with an actual tube model? You can find symbols for triodes, tetrodes and pentodes in the LTspice installation (look in the "Misc" category), and models in the files section of the group site. You can search for them with your browser by opening: http://groups.yahoo.com/neo/groups/LTspice/files/%20%20Tables%20of%20Contents/all_files.htm Regards, Tony |
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Re: A three Phase question please
John Woodgate
In message <1387825178.9799.YahooMailNeo@...>, dated Mon, 23 Dec 2013, kim nielsen <dkkiboni@...> writes:
Maybe a resistor across etch diode, but I think it is not necessary, the leakage current is big enough to balance the voltage across the diodes. Have used about 100,000 diode without resistor and not a single diode failed because of the voltage across them. The VR37 is big and expensive and sometimes hard to come by.4 mm x 9 mm, about USD0.25 50-off. If you open op a TV20 (20KV) diode there is also not a resistor across each diodeThose are checked for balanced reverse voltage distribution. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Nondum ex silvis sumus John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK |
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Re: A three Phase question please
Hi John Maybe a resistor across etch diode, but I think it is not necessary, the
leakage current is big enough to balance the voltage across the diodes. Have
used about 100,000 diode without resistor and not a single diode failed because
of the voltage across them. The VR37 is big and expensive and sometimes hard to
come by. If you open op a TV20 (20KV) diode there is also not a resistor across each
diode. ? ? Med venlig hilsen, Kinds regards
Kim Borg Nielsen On Monday, December 23, 2013 7:38 PM, John Woodgate wrote:
?
In message , dated Mon, 23
Dec 2013, Michael Peter writes: >While following this thread, it just dawned on me that I do not know >how to measure 3 phase power.? Any suggestions how to do this in real >life and ofcourse in LTspice as well. >? In real life, use two wattmeters. Call the phases A, B and C. One meter has its current coil in phase A and its voltage coil between A and C. The other meter has its current coil in phase B and its voltage coil between B and C. The power is the sum of the two meter readings. This works for a balanced or unbalanced load, star/wye or delta connected. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Nondum ex silvis sumus John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK |
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Re: A three Phase question please
John Woodgate
In message <DUB110-W214CEC96F96D0814B332F3ACC10@...>, dated Mon, 23
Dec 2013, Michael Peter <michael883575@...> writes: While following this thread, it just dawned on me that I do not knowIn real life, use two wattmeters. Call the phases A, B and C. One meter has its current coil in phase A and its voltage coil between A and C. The other meter has its current coil in phase B and its voltage coil between B and C. The power is the sum of the two meter readings. This works for a balanced or unbalanced load, star/wye or delta connected. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Nondum ex silvis sumus John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK |
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Re: A three Phase question please
¿ªÔÆÌåÓýMeasuring 3-Phase power is exactly the same as measuring single-phase power, except you have to do it 3 times.In practice you need a measurement set-up that monitors the vectorial product of voltage and current. It could be an electrodynamic dual-coil meter, or a digital wattmeter. In LTspice, use the standard method thrice. Le 23/12/2013 18:36, Michael Peter a
crit:
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Re: A three Phase question please
¿ªÔÆÌåÓýWhile following this thread, it just dawned on me that I do not know how to measure 3 phase power.? Any suggestions how to do this in real life and ofcourse in LTspice as well. ? Michael ? To: LTspice@... From: jmw@... Date: Sun, 22 Dec 2013 15:41:16 +0000 Subject: Re: [LTspice] RE: A three Phase question please ?
In message <1387726122.76180.YahooMailNeo@...>,
dated Sun, 22 Dec 2013, kim nielsen writes: >Use UF4007(SF4007), they are 1A, 1000V, 75nS Trr and cheap. 1n4148 have >only 75volt reveres voltage. > >10pcs. in series gives 10KV. I would use 11 to have som margen. Even so, I would put 1 meg resistors **rated for 1000 V at least** across each diode. Vishay VR37 type, for example. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Nondum ex silvis sumus John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK |
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Re: CIC unstable output
Hello John I wish the wealth of information that can be found over the Internet could let me know about the exact nature of the problem LTspice shows for this particular schematic. > It might be helpful if you describe in detail the discrete > digital structure that you are trying to simulate. Thinking of sparing you all of possible errors from my English I uploaded CIC.asc in Temp. It may still be there, I haven't checked.? > I have always found it challenging to translate discrete digital > filters back into the analog for simulation. > Perhaps the problem is that the analog nature of the delay lines > allows small errors to grow due to the very high gain So then part of the suspicion is true, LTspice is dedicated to analog simulation, despite all the efforts. It still is strange that using Filter with a 4 times interpolator, N=256 FIR will show no such odditites as CIC does, no matter how long the simulation. But it's also true that the CIC uses integrators while the FIR uses no feedback. > Maybe buffering the output with quantizing b-source would help > (one that can only take on valid digital values) I'll try using int() to force some would-be quantizing, but later. For now a break. Thank you all for the advises and a Merry Christmas. Vlad |
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Re: CIC unstable output
This is from my phone, so it may be abreviated and spelled poorly. Perhaps the problem is that the analog nature of the delay lines allows small errors to grow due to the very high gain. Maybe buffering the output with quantizing b-source would help (one that can only take on valid digital values).
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Re: JFET Model
That was easy thanks. Chris? On Sun, Dec 22, 2013 at 3:56 PM, <helmutsennewald@...> wrote:
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Tony Casey