In article <sfmund5j3fjc15565a1j97oo524m0akrgq@4ax.com>, boB@K7IQ.com says...> > I remember squegging. Didn't remember snivet though. Very useful > word !Rang a bell with me too, though I didn't remember the definition. It is in my 1962 "A Dictionary of Electronics" paperback (7/6d Penguin) whereas "snivet" isn't. Mike.
Negative resistance with BJTs
Started by ●August 22, 2018
Reply by ●August 24, 20182018-08-24
Reply by ●August 24, 20182018-08-24
On Friday, August 24, 2018 at 2:31:38 AM UTC-4, Tom Del Rosso wrote:> Phil Hobbs wrote: > > On 08/22/2018 07:57 PM, Tom Del Rosso wrote: > >> pcdhobbs@gmail.com wrote: > >>>>> You can also do it with a single transistor at AC. > >>> > >>>> Out of curiosity: do what? > >>> > >>> Make a negative resistor. Start with an emitter follower and put a > >>> small capacitance on the emitter. The input resistance goes > >>> negative. That's why you have to use beads, anti-snivet resistors, > >>> and so on. > >> > >> Snivet? > > > > Oscillation in a power transistor, especially a power MOSFET. (Pease, > > P. 88.) > > Well that's very different from the other answers. You mean this is a > characteristic of the transistor by itself, under certain conditions, > regardless of the circuit? > > Which Pease book? I know of one but I thought there was another.I assume the trouble shooting one. I bought another Pease book... Analog circuits (world class designs). Totally NOT worth it. George H.
Reply by ●August 24, 20182018-08-24
On 08/23/2018 09:08 PM, boB wrote:> On Thu, 23 Aug 2018 09:29:35 -0700, John Larkin > <jjlarkin@highlandtechnology.com> wrote: > >> On Wed, 22 Aug 2018 21:00:38 -0500, "Tim Williams" >> <tiwill@seventransistorlabs.com> wrote: >> >>> "Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com> wrote in >>> message news:plkt8p$vtq$1@dont-email.me... >>>> pcdhobbs@gmail.com wrote: >>>>>>> You can also do it with a single transistor at AC. >>>>> >>>>>> Out of curiosity: do what? >>>>> >>>>> Make a negative resistor. Start with an emitter follower and put a >>>>> small capacitance on the emitter. The input resistance goes negative. >>>>> That's why you have to use beads, anti-snivet resistors, and so on. >>>> >>>> Snivet? >>>> >>> >>> Hah, Phil's showing his age\\\experience? :-) >>> >>> "Snivets" was an oscillation that sometimes affected vacuum tube television >>> sets, where the horizontal sweep driver had UHF oscillations for part of its >>> operating cycle, apparently due to the cavity formed between screen and >>> plate, and the exact electron beam density and electrode voltages applied. >> >> My uncle Sheldon, the TV repair rascal that taught me electronics, >> called the vertical bars, from HOT oscillations, "squegging." >> >> > > > I remember squegging. Didn't remember snivet though. Very useful > word ! > > Just found this site.... > http://www.eenewsanalog.com/news/electronic-slang-old-and-young-0/page/0/4# > > > snivet > > A short burst of spurious oscillatory circuit behavior. > > “A snivet appears on the output waveform when it crosses zero.” > > > spudger > > An adjustment tool of variable capacitors or inductors that is > nonmetallic and nonconducting so that it will not influence the > adjusted value. Spudgers are usually made of plastic and thus have a > permeability close to that of air. > > squegging > > Spurious frequency modulation in an oscillator caused by noise or > instability. > > “The high-voltage supply is squegging in this ‘scope, causing the > intensity and focus to vary.” > >Squegging is specifically caused by the bias time constant being too long. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●August 24, 20182018-08-24
On 08/24/2018 02:31 AM, Tom Del Rosso wrote:> Phil Hobbs wrote: >> On 08/22/2018 07:57 PM, Tom Del Rosso wrote: >>> pcdhobbs@gmail.com wrote: >>>>>> You can also do it with a single transistor at AC. >>>> >>>>> Out of curiosity: do what? >>>> >>>> Make a negative resistor. Start with an emitter follower and put a >>>> small capacitance on the emitter. The input resistance goes >>>> negative. That's why you have to use beads, anti-snivet resistors, >>>> and so on. >>> >>> Snivet? >> >> Oscillation in a power transistor, especially a power MOSFET. (Pease, >> P. 88.) > > Well that's very different from the other answers. You mean this is a > characteristic of the transistor by itself, under certain conditions, > regardless of the circuit?Yes. The input resistance goes negative when you put a resistor in series with the source.> > Which Pease book? I know of one but I thought there was another."Troubleshooting Analog Circuits", i.e. the good one. His other two are junk--I bought "Analog Circuits (World Class Designs)" and chucked it out within a day or two, and his book on driving "How to drive into accidents and how not to" is a turgid mess. Ironically Pease died by crashing a horribly unsafe car (a '69 Beetle) into a tree on the way to Jim Williams's wake. :( Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●August 24, 20182018-08-24
On Fri, 24 Aug 2018 11:32:38 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 08/24/2018 02:31 AM, Tom Del Rosso wrote: >> Phil Hobbs wrote: >>> On 08/22/2018 07:57 PM, Tom Del Rosso wrote: >>>> pcdhobbs@gmail.com wrote: >>>>>>> You can also do it with a single transistor at AC. >>>>> >>>>>> Out of curiosity: do what? >>>>> >>>>> Make a negative resistor. Start with an emitter follower and put a >>>>> small capacitance on the emitter. The input resistance goes >>>>> negative. That's why you have to use beads, anti-snivet resistors, >>>>> and so on. >>>> >>>> Snivet? >>> >>> Oscillation in a power transistor, especially a power MOSFET. (Pease, >>> P. 88.) >> >> Well that's very different from the other answers. You mean this is a >> characteristic of the transistor by itself, under certain conditions, >> regardless of the circuit? > >Yes. The input resistance goes negative when you put a resistor in >series with the source. > >> >> Which Pease book? I know of one but I thought there was another. > >"Troubleshooting Analog Circuits", i.e. the good one. His other two are >junk--I bought "Analog Circuits (World Class Designs)" and chucked it >out within a day or two, and his book on driving "How to drive into >accidents and how not to" is a turgid mess. Ironically Pease died by >crashing a horribly unsafe car (a '69 Beetle) into a tree on the way to >Jim Williams's wake. :( > >Cheers > >Phil HobbsWe used to drive past his house now and then. The yard and neighborhood were littered with rusty old VW beetles and vans in various states of disrepair. The one that he was driving at the time was literally packed with papers and junk; there was one skinny clear spot on the drivers' seat. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●August 24, 20182018-08-24
In article <sfmund5j3fjc15565a1j97oo524m0akrgq@4ax.com>, boB <boB@K7IQ.com> wrote:>I remember squegging. Didn't remember snivet though. Very useful >word ! > >Just found this site.... >http://www.eenewsanalog.com/news/electronic-slang-old-and-young-0/page/0/4# > > >snivet > >A short burst of spurious oscillatory circuit behavior. > >�A snivet appears on the output waveform when it crosses zero.�I encountered some BJT-related snivets a few years ago, when a retiring ham gave me a two-tone audio oscillator intended for doing amplifier intermod-distortion analysis. He said he'd never been able to get it operate stably - the audio frequencies jumped around a lot for no apparent reason. I looked at it with a fast 'scope and an RF spectrum analyzer, and found that the audio waveforms would break into a burst of VHF oscillation around the point of their minimum output voltage. I could shift the VHF parasitic oscillation (and even change the audio frequency of oscillation!) by waving my fingers near the wiring or lightly touching the components. The circuit was out of QST magazine, and used a pair of twin-T oscillators based on 2N2222 transistors (real, genuine metal-case jobbies no less). As I recall, the twin-T circuit they'd chosen had a capacitor from the transistor base, to ground... a notorious cause of instability. The transistors were socketed, with fairly long leads (and significant lead inductance)... another warning sign. I stuck ferrite beads around the base leads (and, I think, the collector leads) of the transistors, to add some VHF loss. The circuit immediately quieted down and behaved like a tame kitten... stable oscillation by both oscillators, no parasitic VHF, no weird jumping-around when I touched the components. Snivets. A *lovely* word indeed.
Reply by ●August 24, 20182018-08-24
On Friday, August 24, 2018 at 9:57:19 AM UTC-4, George Herold wrote:> On Friday, August 24, 2018 at 2:31:38 AM UTC-4, Tom Del Rosso wrote: > > Phil Hobbs wrote: > > > On 08/22/2018 07:57 PM, Tom Del Rosso wrote: > > >> pcdhobbs@gmail.com wrote: > > >>>>> You can also do it with a single transistor at AC. > > >>> > > >>>> Out of curiosity: do what? > > >>> > > >>> Make a negative resistor. Start with an emitter follower and put a > > >>> small capacitance on the emitter. The input resistance goes > > >>> negative. That's why you have to use beads, anti-snivet resistors, > > >>> and so on. > > >> > > >> Snivet? > > > > > > Oscillation in a power transistor, especially a power MOSFET. (Pease, > > > P. 88.) > > > > Well that's very different from the other answers. You mean this is a > > characteristic of the transistor by itself, under certain conditions, > > regardless of the circuit? > > > > Which Pease book? I know of one but I thought there was another. > > I assume the trouble shooting one. > I bought another Pease book... > Analog circuits (world class designs). Totally NOT worth it. > > George H.Hey speaking of trouble shooting, I found a new one (for me) today. 74HC14 was being powered by it's input pulses. (I forgot to hook up the 5V rail.) George H.
Reply by ●August 24, 20182018-08-24
George Herold <gherold@teachspin.com> wrote:> On Friday, August 24, 2018 at 9:57:19 AM UTC-4, George Herold wrote: >> On Friday, August 24, 2018 at 2:31:38 AM UTC-4, Tom Del Rosso wrote: >> > Phil Hobbs wrote: >> > > On 08/22/2018 07:57 PM, Tom Del Rosso wrote: >> > >> pcdhobbs@gmail.com wrote: >> > >>>>> You can also do it with a single transistor at AC. >> > >>> >> > >>>> Out of curiosity: do what? >> > >>> >> > >>> Make a negative resistor. Start with an emitter follower and put a >> > >>> small capacitance on the emitter. The input resistance goes >> > >>> negative. That's why you have to use beads, anti-snivet resistors, >> > >>> and so on. >> > >> >> > >> Snivet? >> > > >> > > Oscillation in a power transistor, especially a power MOSFET. (Pease, >> > > P. 88.) >> > >> > Well that's very different from the other answers. You mean this is a >> > characteristic of the transistor by itself, under certain conditions, >> > regardless of the circuit? >> > >> > Which Pease book? I know of one but I thought there was another. >> >> I assume the trouble shooting one. >> I bought another Pease book... >> Analog circuits (world class designs). Totally NOT worth it. >> >> George H. > > Hey speaking of trouble shooting, I found a new one (for me) > today. 74HC14 was being powered by it's input pulses. > (I forgot to hook up the 5V rail.)https://www.youtube.com/watch?v=2yFh7Vv0Paw
Reply by ●August 24, 20182018-08-24
George Herold wrote:> > Hey speaking of trouble shooting, I found a new one (for me) > today. 74HC14 was being powered by it's input pulses. > (I forgot to hook up the 5V rail.)That's in every edition of AoE!
Reply by ●August 24, 20182018-08-24
Phil Hobbs wrote:> > "Troubleshooting Analog Circuits", i.e. the good one. His other two > are junk--I bought "Analog Circuits (World Class Designs)" and > chucked it out within a day or two, and his book on driving "How to > drive into accidents and how not to" is a turgid mess. Ironically > Pease died by crashing a horribly unsafe car (a '69 Beetle) into a > tree on the way to Jim Williams's wake. :(I gave that book to a non-driver as a gift. I never had the heart to tell her... IIRC it was after he left the wake. Wasn't he assumed to have had a heart attack since no other cars were involved?
