the Chopper Amplifier ? who was first ? see this teardown video 1961

[oz2cpu]

this design is from 1961
see the video about 20 mins
https://youtu.be/txfpbSDGik4

where the mecanic chopper is shown first time,
it is actually a very special relay, that chop up the milivolts of DC into AC
now 4 tubes can amplify and use feedback, for stable readout (stable gain)

when was chopper invented ?
where did you see it first ?

[TimFox]

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 Wallman Vacuum 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 Jr Electronic Instruments McGraw-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 Devices  https://www.analog.com/media/en/training-seminars/design-handbooks/Op-Amp-Applications/SectionH.pdf  discusses chopper stabilization of vacuum tube operational amplifiers, putting the start date as 1949.  (pp H17 ff).

[oz2cpu]

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

[TimFox]

I must admit that I don't remember 1949, since I was born in November of that year.

[oz2cpu]

great Tim, that means you will find alot of familiar or fun or interesting things in my teardown playlist
please feel free to browse thru it.

the next few days i release some new videos about equipment from 195x

[TimFox]

By the way, I didn't locate any other historical references to the two "vibrators", Brown Converter and Leeds and Northrup, cited in the Rad Lab books.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 file  http://philbrickarchive.org/thecontactmodulator_ocr.pdf  is 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.)

[oz2cpu]

you are right : the first pen writers used a mecanical osc pwm generator and a feedback potentiometer
to drive the motors, and compare the position to incomming voltage.
still on my most wanted list to try and test and teardown my self :-)

[oz2cpu]

here you go Tim

more great fun

HP 200CD wide range oscillator  5Hz-600kHz

https://youtu.be/vnRUzsWTnlY

original design 1955, last design 1965
extreamly accurate frequency setting
funny error found in schematic :-)

the video to be released tomorrow, go at least 5 more years older :-)

[mawyatt]

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 Time

Best,

[TimFox]

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.

[mawyatt]

Yep, she single handed destroyed a Technology Icon and ended up with just another computer company that happened to make good printers

Best,

[oz2cpu]

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 funny
maybe you agree it is a classic valve upgrade problem :-)
----------------
today video release is here:
https://youtu.be/2GvWW7eWQDI
Radiometer RV33 vacuum tube voltmeter
i 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