the Chopper Amplifier ? who was first ? see this teardown video 1961 - Page 1
Forum section: electronics / projects

author: oz2cpu
author_rank: Frequent Contributor
timestamp: April 28, 2022, 03:12:33 pm
content: this design is from 1961see the video about 20 minshttps://youtu.be/txfpbSDGik4where the mecanic chopper is shown first time,it is actually a very special relay, that chop up the milivolts of DC into ACnow 4 tubes can amplify and use feedback, for stable readout (stable gain)when was chopper invented ?where did you see it first ?

author: TimFox
author_rank: Super Contributor
timestamp: April 28, 2022, 03:52:19 pm
content: Electromechanical choppers for DC stabilization of vacuum-tube amplifiers are discussed in the post-WWII Radiation Laboratory Series books from the radar laboratory at MIT.See: G E Valley Jr and H WallmanVacuum Tube Amplifiers, McGraw-Hill 1948, p 490 for a unique circuit (not using a chopper) in a DC amplifier.Also, I A Greenwood Jr, J V Holdam Jr, and D MacRae JrElectronic InstrumentsMcGraw-Hill 1948, where section 15-4 (pp 511 - 519) discusses "comparison circuits" that includes the Brown Converter and Leeds and Northrup vibrators. Practical DC precision power supply circuits using choppers are discussed in section 16-6 (pp 548 - 555), where one uses a Brown Converter.Post-war, they became used in vacuum-tube operational amplifiers in analog computers.I assume that the term "vibrator" used in the second book reflects the similarity to the vibrators used in car radios, etc., with a step-up transformer to obtain plate voltage supply from a low-voltage DC source (car battery).In operational amplifiers, the term "chopper" became more common.A history of op amps written by Jung for Analog Deviceshttps://www.analog.com/media/en/training-seminars/design-handbooks/Op-Amp-Applications/SectionH.pdfdiscusses chopper stabilization of vacuum tube operational amplifiers, putting the start date as 1949. (pp H17 ff).

author: oz2cpu
author_rank: Frequent Contributor
timestamp: April 28, 2022, 04:14:19 pm
content: wow thanks 1949 :-)and i do remember pulling apart tube car radio sets when i was i kid,the vibrator was clearly the most cool thing to pull out and see how it worked

author: TimFox
author_rank: Super Contributor
timestamp: April 28, 2022, 04:17:02 pm
content: I must admit that I don't remember 1949, since I was born in November of that year.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: April 28, 2022, 04:37:24 pm
content: great Tim, that means you will find alot of familiar or fun or interesting things in my teardown playlistplease feel free to browse thru it.the next few days i release some new videos about equipment from 195x

author: TimFox
author_rank: Super Contributor
timestamp: April 28, 2022, 05:03:57 pm
content: By the way, I didn't locate any other historical references to the two "vibrators", Brown Converter and Leeds and Northrup, cited in the Rad Lab books.I assume they were introduced before the war for use in pen recorders for industrial monitoring, probably in servo circuits with feedback from a potentiometer linked to the pen position.The first document in a very large filehttp://philbrickarchive.org/thecontactmodulator_ocr.pdfis an early 1960s publication from Airpax, an important manufacturer of choppers for DC amplifiers, which states that their usage started in about 1948. (It also mentions early transistor choppers.)

author: oz2cpu
author_rank: Frequent Contributor
timestamp: April 28, 2022, 07:46:06 pm
content: you are right : the first pen writers used a mecanical osc pwm generator and a feedback potentiometerto drive the motors, and compare the position to incomming voltage.still on my most wanted list to try and test and teardown my self :-)

author: oz2cpu
author_rank: Frequent Contributor
timestamp: April 29, 2022, 05:00:41 pm
content: here you go Timmore great funHP 200CD wide range oscillator 5Hz-600kHzhttps://youtu.be/vnRUzsWTnlYoriginal design 1955, last design 1965extreamly accurate frequency settingfunny error found in schematic :-)the video to be released tomorrow, go at least 5 more years older :-)

author: mawyatt
author_rank: Super Contributor
timestamp: April 29, 2022, 05:26:55 pm
content: What a magnificent instrument the 200CD was. At Keysight's Santa Rosa Research Facility they have the 200CD's predecessor, the 200CD, and a whole lot more in a Time Line as you walk down the main isle. It's like taking a walk thru Technology TimeBest,

author: TimFox
author_rank: Super Contributor
timestamp: April 29, 2022, 05:30:18 pm
content: I remember when Carly (of cursed memory) was wresting control of Hewlett Packard from the two families, she ran ads in the business sections with a beat-up original model 200A oscillator, with octal tubes, asking rhetorically if -hp- should have remained a manufacturer of such things. At the time, the 200 series held the record for most years in production for that kind of thing.

author: mawyatt
author_rank: Super Contributor
timestamp: April 29, 2022, 05:46:23 pm
content: Yep, she single handed destroyed a Technology Icon and ended up with just another computer company that happened to make good printersBest,

author: oz2cpu
author_rank: Frequent Contributor
timestamp: April 30, 2022, 07:37:56 am
content: you find a few more HP items in my playlist, some with tubes too..did you also find the reversed diodes in the schematic HP 200 CD funnymaybe you agree it is a classic valve upgrade problem :-)----------------today video release is here:https://youtu.be/2GvWW7eWQDIRadiometer RV33 vacuum tube voltmeteri think this one of from 1950 to 1956 see the schematic at end of video,the switch needs more cleaning, then i think this one will work again