Tube vs. Solid State Preamp
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From: Phil Hobbs on 1 Apr 2010 19:14 On 4/1/2010 6:49 PM, Tim Williams wrote: > "Phil Hobbs"<pcdhSpamMeSenseless(a)electrooptical.net> wrote in message > news:4BB51FFB.40407(a)electrooptical.net... >> one possibility would be a gallium field emitter, as used in focused ion >> beam milling machines--you make a needle with a dimple in the end, and the >> electric field pulls it into an atomically-sharp point. A very cool >> demonstration of electrostatics! > > Oh yeah, those are neat! > > Gallium ions would be even lower 'mobility' though (or since it's ballistic > rather than resistive trajectory, should that be 'ballisticity'?). > > What happens when it runs out, though? I've got 12AX7s that have conducted > more than a few farads of charge. Eventually you get a cathode spattered > with gallium (or amorphosized with gallium deposition competing with > sputtered substrate). Just let it drip to the bottom like the old mercury > toobs? > > What's the vapor pressure of molten gallium, anyway? Lesse, 'Pedia says 1Pa > at 1310K... probably not a big deal at 25C. Actual operating temperature > could be high or low, depending on how you seal the thing... if you build it > like an ordinary tube and dissipate real power, it could get quite hot. Or > you could make it like a TO-247 with a small bell jar, keeping the cathode > arbitrarily cold. > > Tim > A coulomb is only 10**-5 mole, but yeah, gallium depletion is an issue. The nice thing is that you don't have to pump. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: Joerg on 1 Apr 2010 19:21 Tim Williams wrote: > "Joerg" <invalid(a)invalid.invalid> wrote in message > news:81kab2Fe80U1(a)mid.individual.net... >> My experience with tantalums is that they are excellent in terms of >> electrical behavior. Until one fine day ... *PHOOMP* > > My understanding is they only go Chernobyl when overheated. So maybe with a > combination of particularly harsh operating conditions in the middle of > Indian summer, a few might pop. As long as you keep RMS amps and operating > temperature within limits, they'll work. > Thing is, you have to voltage-derate them big time even if the ripple is well within datasheet limits. "Yeah, you can go 130mph but only on Sundays, else the engine might seize" > I haven't had one explode on me yet, but I haven't used many, either. I've > seen a few pieces of equipment that cooked them, but far more that haven't > failed, and haven't had one go off in front of me. I must admit the horror > stories have me scared... > I've seen a production guy whose shirt was ruined, the tantalum splatters etches their way through. If he hadn't worn glasses, oh boy ... -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 1 Apr 2010 20:06 On Thu, 1 Apr 2010 16:12:21 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"Joerg" <invalid(a)invalid.invalid> wrote in message >news:81kab2Fe80U1(a)mid.individual.net... >> My experience with tantalums is that they are excellent in terms of >> electrical behavior. Until one fine day ... *PHOOMP* > >My understanding is they only go Chernobyl when overheated. So maybe with a >combination of particularly harsh operating conditions in the middle of >Indian summer, a few might pop. As long as you keep RMS amps and operating >temperature within limits, they'll work. Dry-slug MnO2 tantalums are fine as long as you don't expose them to too much dV/dT, namely too much current. That means they aren't usually suited for bypassing power rails. Derating 3:1 on voltage does seem to make them safe. Sometimes that's worth it. They have fairly stable ESRs over temperature, and work at -20 or -40C when aluminums quit. John
From: VWWall on 1 Apr 2010 20:40 Jim Thompson wrote: > On Thu, 01 Apr 2010 14:34:37 -0700, VWWall <vwall(a)large.invalid> > wrote: > >> Joerg wrote: >>> Jim Thompson wrote: >>>> Size? Ever see a Nuvistor ?:-) >>>> >>> Yup, used them. In fact, one of my RF tools here (a dipmeter) has one in >>> there except they called them acorn tube in them's days. >>> >> Acorn tubes and Nuvistors were very different things. Acron tubes were >> used in a direction finder loop pre-amp that I used in the U. S. Army >> Signal Corps in 1943-1945 in North Africa and Italy. They were 954 and >> 955, glass envelope tubes with element connections out the side and top. >> They *were* in the shape of acorns. >>>> And I can't remember what they were called... a stack of ceramic >>>> spacers and metal grids... really small. One jokester had the >>>> "heater" from a blowtorch ;-) >>>> >> A Nuvister was a small ceramic vacuum tube. The last one I saw was used >> in my garage door opener receiver. When it failed, I couldn't find a >> replacement and had to replace the whole receiver with a transistorized one. >>> That I don't remember. I'm not _that_ old :-)) >>> >> I was at Bell Labs when transistors were young, and have taught >> transistor electronics at UCLA Extension, but most of my career has >> included vacuum tubes from magnetrons to traveling wave tubes. >> >> I'm older than either of you! :-( > > Not by much! IIRC you said something like 74?? I'm 70. > How old do you think I was when being shot at in North Africa with the Signal Corps? I did enlist at seventeen, but that was almost 70 years ago. My brother's 15 months younger, and lives in Scottsdale. He owned the Ethan Allen furniture store in Phoenix and Mesa. -- Virg Wall
From: krw on 1 Apr 2010 20:45
On Thu, 01 Apr 2010 15:35:33 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Thu, 01 Apr 2010 14:34:37 -0700, VWWall <vwall(a)large.invalid> >wrote: > >>Joerg wrote: >>> Jim Thompson wrote: >>>> >>>> Size? Ever see a Nuvistor ?:-) >>>> >>> >>> Yup, used them. In fact, one of my RF tools here (a dipmeter) has one in >>> there except they called them acorn tube in them's days. >>> >>Acorn tubes and Nuvistors were very different things. Acron tubes were >>used in a direction finder loop pre-amp that I used in the U. S. Army >>Signal Corps in 1943-1945 in North Africa and Italy. They were 954 and >>955, glass envelope tubes with element connections out the side and top. >> They *were* in the shape of acorns. >>> >>>> And I can't remember what they were called... a stack of ceramic >>>> spacers and metal grids... really small. One jokester had the >>>> "heater" from a blowtorch ;-) >>>> >>A Nuvister was a small ceramic vacuum tube. The last one I saw was used >>in my garage door opener receiver. When it failed, I couldn't find a >>replacement and had to replace the whole receiver with a transistorized one. >>> >>> That I don't remember. I'm not _that_ old :-)) >>> >>I was at Bell Labs when transistors were young, and have taught >>transistor electronics at UCLA Extension, but most of my career has >>included vacuum tubes from magnetrons to traveling wave tubes. >> >>I'm older than either of you! :-( > >Not by much! IIRC you said something like 74?? I'm 70. Wow! ...and I remember your 16th birthday. |