Twin T circuit wanted
in [Design]
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From: BlindBaby on 10 Jun 2010 21:07 On Thu, 10 Jun 2010 19:03:28 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Thu, 10 Jun 2010 15:53:53 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Thu, 10 Jun 2010 12:50:00 -0700 (PDT), dagmargoodboat(a)yahoo.com >>wrote: >> >>>John Larkin wrote: >>>> dagmargoodb...(a)yahoo.com wrote: >>>> >>>> >On Jun 9, 9:18 pm, Winfield Hill wrote: >>> >>>> >> Picky, picky. To my mind, the base current robbed by the >>>> >> collector starves the base, lowering the CE stage's gain, >>>> >> until the exact equilibrium is achieved. ALC, AGC, pick >>>> >> your name as you like. Either way it gets the job done >>>> >> rather nicely, and is a bit different from what we've seen >>>> >> elsewhere, such as in old radio circuits. I see that it >>>> >> has been analyzed as a possible RF oscillator technique. >>>> >> But it seems to me that, working as we imagine, Vce(sat) >>>> >> and all, this trick would be limited to far far below fT. >>>> >>>> >Just to clarify, the RF versions I posted are similar to, but not the >>>> >same as John's. �They're standard UHF designs, Class A, without John's >>>> >precision AGC. �I don't think they can use John's AGC method directly-- >>>> >if saturated, the transistors would be too slow--but maybe a Baker-ish >>>> >clamp thing would do the job. >>>> >>>> In my oscillator, a c-b schottky diode would keep the transistor c-b >>>> junction from conducting, and keep the transistor out of saturation. >>>> Tempco would still be low. That simplifies things considerably. Not >>>> bad. >>> >>>Good idea. >>> >>>> >Oh, and John's oscillator really swings ~ 2* (Vcc + Vbe), not 2* (Vcc >>>> >- Vbe). �Reason being, the AGC operates as the average base voltage >>>> >gets sucked down to near 0v, killing the gain. >>>> >>>> I seem to recall the DC base voltage being about +.6. So the collector >>>> swings to just about zero, and the AC output is 2*Vcc p-p. Somebody >>>> could Spice this, if they were interested, and see exactly what >>>> happens. >>> >>>I Spice'd all the circuits I posted. >>> >>>> The transformer ratio gets involved some, too. >>> >>>Yep, but to a 1rst order: average emitter voltage = 0, ignore the >>>swing 'cause it's small, and that gets you pretty close. V(b) = 120mV >>>in my 5KHz example. >>> >>>James >> >>How much p-p voltage on the emitter? >> >>That low a DC base voltage suggests more like class-C action. With >>less turns on the emitter winding, the thing gets more class A-ish, >>and I'd expect the DC base voltage to go up some. I think. >> >>I wonder what happens to the DC base voltage as the base bias resistor >>changes. I'm not even sure which direction things will go. >> >>Complicated, for 5 parts. > >--- >So, _there's_ a "circuit designer" who can't even figure out how a >circuit which he's put into the world works, and yet wants to elevate >himself into the position of a judge of circuit designs? And circuit design tools as well.
From: Jim Thompson on 10 Jun 2010 21:10 On Thu, 10 Jun 2010 20:58:49 -0300, YD <ydtechHAT(a)techie.com> wrote: >Late at night, by candle light, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> penned this >immortal opus: [snip] >> >>Larkin copies circuits from others, Rohde in this case, then totally >>blows the explanation. >> >>Then, unfortunately, Win has backed up the BAD explanation :-( >> >> ...Jim Thompson > >So cough up the GOOD explation, or shut up. > [snip jerkism] > >-YD. YD is normally blocked. Since JL responded... I will, in due course. I'm waiting, and hoping, that some young buck has a clear head, and can analyze it. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: John Larkin on 10 Jun 2010 21:11 On Thu, 10 Jun 2010 17:21:02 -0700 (PDT), MooseFET <kensmith(a)rahul.net> wrote: >On Jun 11, 12:01 am, John Larkin >[....] >> I don't think so. People designed radar, magnetrons and klystrons and >> waveguides and servos and all that, without computers. They did the >> math. Early computers were obviously designed without help from >> computers. > ><PITA> >Make that "electronic computers". At one time, a computer was >a person who computed. Companies had rooms full of people >grinding through the numbers to make sure that the sums were >right. ></PITA> <OLDFARTSTORY> My first real job was a research assistant in microwave spectroscopy, a summer tech job. Two grad students on the same project spent the entire summer hunched over a Friden calculator in a small room, calculating rotational resonances for some organic thing. My PC could do all that now in, probably, a millisecond. </OLDFARTSTORY> > >There were also some analog computers and mechanical >computers. Each generation has used the tools made by >the previous. Just try to imagine designing with Roman >numerals and not even a slide rule. > > >> I don't use Spice a lot, and could certainly get along without it. It >> is helpful when evaluating nonlinear systems, where math solutions >get messy. > >I use spice as a sanity check. Sometimes it even finds some. > >LTSpice is also nice for making a schematic to email to someone. It is just about the only portable schematic format the industry has ever seen. Not a bad editor, but the circuits seem to wander all over the screen as you zoom. I have to keep selecting my whole circuit and dragging it back into sight. John
From: John Larkin on 10 Jun 2010 21:13 On Thu, 10 Jun 2010 17:37:34 -0700 (PDT), MooseFET <kensmith(a)rahul.net> wrote: >On Jun 10, 11:06 pm, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >[....] >> Can you think of other ways to make a very frequency and amplitude >> stable sine wave using early-70s technology? I suppose that a square >> wave generator and bandpass filter would work, but that's more parts. > >A tuning fork "self hummer" circuit using inductive drive and >inductive pick-up could be quite frequency stable. > >Amplitude stability comes from making the >cathode current on the 6SN7 nearly constant with >a really high voltage supply and a large resistor. > > What would determine the sinewave amplitude? John
From: Jim Thompson on 10 Jun 2010 21:16
On 10 Jun 2010 17:55:23 -0700, Winfield Hill <Winfield_member(a)newsguy.com> wrote: >John Larkin wrote... >> >> I have never called myself a "judge", and Win has never called >> himself a "master." You and JT call us that, so you can then >> abuse us for saying things we never said. How lame. > > That's correct. I work hard at what I do, but I'm always > on the lookout for mistakes I may make, or more often, > things I don't yet understand. Hopefully I'll not pipe > up about something I don't yet understand, but oops, oops, > sometimes one doesn't yet know that they don't understand > something, or they may just make a silly thoughtless mistake. Yep. "Ooopses" happen. As soon as I describe it on Sunday or Monday, you'll see how simple it is to understand. Off to SFO at dawn... NO I'm not seeing Larkin... I'm heading to Palo Alto ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy |