Twin T circuit wanted
in [Design]
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From: Grant on 11 Jun 2010 04:31 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. They used to make little audio freq. tuning modules for old style answer machine security (!) code. Two tuning forks per portable unit about the size of the old 6 transistor radio, they were about the size of the radio metal can coils but maybe three or four times longer. Saw them on Voca equipment back 35 years ago. Very clear notes, but slow (seconds) to build up amplitude. I suppose along lines of DTMF, but before the chips could makes the tones came out. Transistorised, no ICs, when PCBs contained masses of transistors and stand up resistors. You played your security tone down the phone line to access the machine, get it to replay messages. Old barrel style fax machines also used them to recognise each other too. Grant. -- http://bugs.id.au/
From: Grant on 11 Jun 2010 04:37 On Thu, 10 Jun 2010 22:16:50 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: .... >I prefer smaller drive, a tenth or so p-p on the emitter. Maybe even >less, basically class A. > >The whole thing behaves differently if the secondary drive is large >and the transistor conduction angle is small: the emitter voltage will >swing down, way below ground, and pull the base down with it before >the collector voltage gets down to ground... blasting a spike of >collector current into the tank. Then it will swing way up and turn >the base off. Brutality! Chaos! > >I prefer a more delicate touch: the collector dips down elegantly, >like a swan landing on a pond. It just barely touches the water, err, >emitter, and together they remove a bit of charge from the base cap. >And then it flies away. Did I mention the sunset in the background? Nice, poetic ;) You see the circuits in the 'air' when you're designing? Grant. -- http://bugs.id.au/
From: John Fields on 11 Jun 2010 08:41 On Thu, 10 Jun 2010 17:44:54 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >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, > >It works fine the way I designed it to work. I admit I don't >understand all the possible variations, and the entire possible >operating envelope, because it didn't matter 35 years ago, and it >doesn't matter now. It's just sort of interesting to discuss. > >Discussion sort of requires that you don't assume you know everything. > > > and yet wants to elevate >>himself into the position of a judge of circuit designs? > >I have never called myself a "judge" --- Perhaps not in so many words, but your neverending patting yourself on the back while demeaning the work of others speaks volumes about what you perceive yourself to be. --- >, 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. --- I've never called you a judge and I've never called Win a master, so it seems _you're_ the one putting words in my mouth so you can create a straw man, you insidious trash. --- >How lame. --- PKB, cheater. --- >Tell us more about tuning fork oscillators. --- Why, when all you're interested in is generating another row? Forget it; I'm done with you for the time being.
From: John Fields on 11 Jun 2010 08:45 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. --- Typical Larkinese tactic; poisoning the well. Better watch out, Win, if you disagree with him he'll more than likely have something nasty and untrue to say about you, too.
From: John Fields on 11 Jun 2010 08:50
On Thu, 10 Jun 2010 18:07:46 -0700, BlindBaby <BlindMelonChitlin(a)wellnevergetthatonethealbumcover.org> wrote: >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: >>>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. --- Yup, and just about everything else in the world. JF |