On 05/07/2016 01:04 AM, bill.sloman@ieee.org wrote:> On Saturday, May 7, 2016 at 1:07:31 PM UTC+10, John Larkin wrote:<sniiip>>> I looked for a manual for the Cary but didn't find one. I think >> maybe a vibrating reed acted like a variable capacitor and >> modulated the input voltage into an AC amplifier. Is that how it >> worked? If so, a vibrating reed with a solid-state amplifier would >> be at least as good as the tube version. > > A changing capacitance in an electric field generates an AC current. > > Analog Devices had a solid state competitor to the vibrating reed > with a back-biased varactor bridge which worked much the same way.Really? The only one of those I remember is the Philbrick P2. 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
nice fA opamp
Started by ●May 5, 2016
Reply by ●May 7, 20162016-05-07
Reply by ●May 7, 20162016-05-07
On Sat, 07 May 2016 11:56:31 -0700, John Larkin <jjlarkin@highlandtechnology.com> wrote:>On Sat, 7 May 2016 13:43:22 -0500, "Tim Williams" ><tiwill@seventransistorlabs.com> wrote: > >><bill.sloman@ieee.org> wrote in message >>news:06598350-1435-4e07-8082-b4bb61041265@googlegroups.com... >>> The Cary would have needed a very low input capacitance amplifier, which >>> would have been easier to realise with a valve/tube back then. >>> >> >>Not as much as you might think: the smallest triodes (like the "acorn" style >>57, 0.3pF G-H, 1.2pF G-P) and "electrometer" types are comparable to what >>you'll get from smaller semiconductors, especially with bootstraps. >> >>Likewise the follower performance of a triode or pentode isn't very good, >>due to the lower gain. >> >>Tim > >I think there were tubes, used for tape head and mic inputs, that got >close to 1 nV/rtHz noise levels.--- Oh, my... I think there were some that were twice that good, but I just can't seem to remember their part numbers. John Fields
Reply by ●May 7, 20162016-05-07
On Sat, 7 May 2016 14:57:27 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 05/07/2016 01:04 AM, bill.sloman@ieee.org wrote: >> On Saturday, May 7, 2016 at 1:07:31 PM UTC+10, John Larkin wrote: ><sniiip> >>> I looked for a manual for the Cary but didn't find one. I think >>> maybe a vibrating reed acted like a variable capacitor and >>> modulated the input voltage into an AC amplifier. Is that how it >>> worked? If so, a vibrating reed with a solid-state amplifier would >>> be at least as good as the tube version. >> >> A changing capacitance in an electric field generates an AC current. >> >> Analog Devices had a solid state competitor to the vibrating reed >> with a back-biased varactor bridge which worked much the same way. > >Really? The only one of those I remember is the Philbrick P2. > >Cheers > >Phil HobbsTI briefly made an integrated opamp that had a varactor-modulator front end. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●May 7, 20162016-05-07
On Friday, May 6, 2016 at 8:07:31 PM UTC-7, John Larkin wrote:> On Fri, 6 May 2016 10:39:41 -0700 (PDT), whit3rd <whit3rd@gmail.com> > wrote: > > >On Thursday, May 5, 2016 at 5:11:43 PM UTC-7, John Larkin wrote: > >> http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overview > >> > >> Input current is typically 0.1 fA at room temp.> >Well, that's getting down there. A fifty-year old Cary 31 electrometer > >has about 1E-18 A input current, so there's only another decade or two > >before solid state catches up. To vacuum tubes. > > > >Gold-plated elecrodes, cast iron case, sapphire insulators... they > >say a lot of the cost is in the packaging.> I looked for a manual for the Cary but didn't find one. I think maybe > a vibrating reed acted like a variable capacitor and modulated the > input voltage into an AC amplifier. Is that how it worked?Yep, that's the principle. The cast-iron probe head, and selected tubes for low microphonics (and there were Nuvistor upgrades recommended) were necessary elements. I found one for the old lab, around thirty years ago, but the manual was a faded mimeograph.
Reply by ●May 8, 20162016-05-08
On Saturday, May 7, 2016 at 11:57:32 AM UTC-7, Phil Hobbs wrote:> On 05/07/2016 01:04 AM, bill.sloman@ieee.org wrote:> > A changing capacitance in an electric field generates an AC current. > > > > Analog Devices had a solid state competitor to the vibrating reed > > with a back-biased varactor bridge which worked much the same way. > > Really? The only one of those I remember is the Philbrick P2.See here: <https://archive.org/details/AnalogDevicesDataAcquisitionProductsCatalog1979> AD310 (inverting) and AD311 (noninverting) were the part numbers. Those, Keithley 427 current amplifiers, and the Cary electrometer were all useful for accurate ion-chamber measurements of X-rays, gammas, C14 dating. The predecessors were gold-leaf electroscopes, used with stopwatches...
Reply by ●May 8, 20162016-05-08
On 05/07/2016 11:10 PM, whit3rd wrote:> On Saturday, May 7, 2016 at 11:57:32 AM UTC-7, Phil Hobbs wrote: >> On 05/07/2016 01:04 AM, bill.sloman@ieee.org wrote: > >>> A changing capacitance in an electric field generates an AC current. >>> >>> Analog Devices had a solid state competitor to the vibrating reed >>> with a back-biased varactor bridge which worked much the same way. >> >> Really? The only one of those I remember is the Philbrick P2. > > See here: <https://archive.org/details/AnalogDevicesDataAcquisitionProductsCatalog1979> > > AD310 (inverting) and AD311 (noninverting) > were the part numbers. Those, Keithley 427 current amplifiers, and > the Cary electrometer were all useful for accurate ion-chamber measurements > of X-rays, gammas, C14 dating. The predecessors were gold-leaf electroscopes, used with > stopwatches... >Cool, thanks. 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 ●June 11, 20162016-06-11
whit3rd wrote:> On Thursday, May 5, 2016 at 5:11:43 PM UTC-7, John Larkin wrote: >> http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overview >> >> Input current is typically 0.1 fA at room temp. Noise and offset specs >> are impressive for a fA opamp. >> >> 0.1 fA is 625 electrons per second. > > Well, that's getting down there. A fifty-year old Cary 31 electrometer > has about 1E-18 A input current, so there's only another decade or two > before solid state catches up. To vacuum tubes. > > Gold-plated elecrodes, cast iron case, sapphire insulators... they > say a lot of the cost is in the packaging. > > The chopper for that old amp operated with a 440 Hz (that's A above > middle C, to a musician) tuning fork oscillator...are you suggesting that one can BUILD one using a tuning fork for the vibrating reed?
Reply by ●June 11, 20162016-06-11
John Larkin wrote:> On Fri, 6 May 2016 10:39:41 -0700 (PDT), whit3rd<whit3rd@gmail.com> > wrote: > >> On Thursday, May 5, 2016 at 5:11:43 PM UTC-7, John Larkin wrote: >>> http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overview >>> >>> Input current is typically 0.1 fA at room temp. Noise and offset specs >>> are impressive for a fA opamp. >>> >>> 0.1 fA is 625 electrons per second. >> >> Well, that's getting down there. A fifty-year old Cary 31 electrometer >> has about 1E-18 A input current, so there's only another decade or two >> before solid state catches up. To vacuum tubes. >> >> Gold-plated elecrodes, cast iron case, sapphire insulators... they >> say a lot of the cost is in the packaging. > > ebay has at least one, but the shipping looks expensive. > >> >> The chopper for that old amp operated with a 440 Hz (that's A above >> middle C, to a musician) tuning fork oscillator. > > I looked for a manual for the Cary but didn't find one. I think maybe > a vibrating reed acted like a variable capacitor and modulated the > input voltage into an AC amplifier. Is that how it worked? If so, a > vibrating reed with a solid-state amplifier would be at least as good > as the tube version. > >Seems that you are spot-on!
Reply by ●June 11, 20162016-06-11
On Sunday, June 12, 2016 at 9:14:57 AM UTC+10, Robert Baer wrote:> whit3rd wrote: > > On Thursday, May 5, 2016 at 5:11:43 PM UTC-7, John Larkin wrote: > >> http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overview > >> > >> Input current is typically 0.1 fA at room temp. Noise and offset specs > >> are impressive for a fA opamp. > >> > >> 0.1 fA is 625 electrons per second. > > > > Well, that's getting down there. A fifty-year old Cary 31 electrometer > > has about 1E-18 A input current, so there's only another decade or two > > before solid state catches up. To vacuum tubes. > > > > Gold-plated elecrodes, cast iron case, sapphire insulators... they > > say a lot of the cost is in the packaging. > > > > The chopper for that old amp operated with a 440 Hz (that's A above > > middle C, to a musician) tuning fork oscillator. > ..are you suggesting that one can BUILD one using a tuning fork for > the vibrating reed?Cary did. The Cary 401 Vibrating Reed Electrometer is firmly embedded in the scientific literature. -- Bill Sloman, Sydney
Reply by ●June 12, 20162016-06-12
On Fri, 06 May 2016 19:43:33 -0500, John Fields <jfields@austininstruments.com> wrote:>On Thu, 05 May 2016 17:11:36 -0700, John Larkin ><jjlarkin@highlandtechnology.com> wrote: >>http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overview >>Input current is typically 0.1 fA at room temp. Noise and offset specs >>are impressive for a fA opamp. >>0.1 fA is 625 electrons per second.>Wowie Zowie... >Show your work. >John FieldsHow to Convert Amps to Electrons Per Second <https://www.youtube.com/watch?v=xPlAHcc4p4o> (1:11) -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
