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Old 6th Jan 2019, 6:41 pm   #1
saddlestone-man
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Default Origin of Class-A, Class-B etc.

Hello All

Does anyone know when and by what individual or official body did the operating conditions of valve and transistor amplifiers get classified into class-a, class-b and so on.

Best rgds. Stef.
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Old 6th Jan 2019, 6:51 pm   #2
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Default Re: Origin of class-a, class-b etc

I suspect Class B kicked it off, when it was devised, the former system being then called Class A by default.
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Old 6th Jan 2019, 9:00 pm   #3
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Default Re: Origin of class-a, class-b etc

So far as I can make out the classification definitions were standardized by the I.R.E. certainly by 1932-1933.

Lawrence.
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Old 6th Jan 2019, 9:01 pm   #4
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Default Re: Origin of class-a, class-b etc

And class C? That probably existed in practice if not in name in early radio transmitters before class B was christened.
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Old 8th Jan 2019, 1:00 pm   #5
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Default Re: Origin of Class-A, Class-B etc.

I was always amazed by the technical description (anode on 50% etc) and somewhere picked up a much simpler description - not sure if it is correct but seemed to suffice in the past

Class A single ended output valve amplifying both sides of the ac signal - like preamp valves.

Class AB multiple versions of the above in parallel.

Class B 2/more valves amplifying half a signal each preceded by a phase splitter - commonly called pushpull.

Class D - think this was chopper type digital where the input signal was chopped up into discrete digital levels and each level amplified, then reconstructed at the output

Probably these are all 'wrong'.
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Old 8th Jan 2019, 1:02 pm   #6
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Default Re: Origin of Class-A, Class-B etc.

Oh and the official descriptions seemed to be in the UK radio amateurs handbook so presumably that body described them originally.
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Old 8th Jan 2019, 1:20 pm   #7
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Default Re: Origin of Class-A, Class-B etc.

When studying the subject the lecturer used the term “angle of flow”, however we never discussed the history to how it all came about.
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Old 8th Jan 2019, 2:24 pm   #8
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Default Re: Origin of Class-A, Class-B etc.

Quote:
Originally Posted by avocollector
Class AB multiple versions of the above in parallel.
No. AB is somewhat ambiguous, but often taken to mean B with a high quiescent current so considerable overlap between the two halves (if audio). Nothing to do with anything in parallel; lots of Class A in parallel is Class A.

Quote:
Class B 2/more valves amplifying half a signal each preceded by a phase splitter - commonly called pushpull.
Almost right, but you can have Class A push pull too. Many lower power PP amps are Class A.

Quote:
Class D - think this was chopper type digital where the input signal was chopped up into discrete digital levels and each level amplified, then reconstructed at the output
Unfortunately Class D seems to have two completely different meanings. For audio it means pulse-width modulation i.e. the audio signal is carried by pulse width rather than voltage level, so it is still an analogue signal even when generated via digital means. There are only two levels: maximum + and maximum -, corresponding to the supply rail voltages.

For radio Class D seems to mean any switching type power amp which is not clearly Class E or F or whatever.
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Old 8th Jan 2019, 3:20 pm   #9
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Default Re: Origin of Class-A, Class-B etc.

Don't forget the suffix 1 or 2. 1 for no grid current, 2 for grid current.
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Old 8th Jan 2019, 7:06 pm   #10
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Default Re: Origin of Class-A, Class-B etc.

I've always been fascinated by "Quiescent-push-pull" as used in 1930s battery radios.

Sort-of Class-B2, intended to save HT-current but because the grids of the P-P stage drew significant grid-current you needed a beefy driver-stage whose demands generally offset the supposed benefits of the output-stage.
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Old 9th Jan 2019, 12:57 pm   #11
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Default Re: Origin of Class-A, Class-B etc.

Quote:
Originally Posted by G8HQP Dave View Post
Quote:
Class D - think this was chopper type digital where the input signal was chopped up into discrete digital levels and each level amplified, then reconstructed at the output
Unfortunately Class D seems to have two completely different meanings. For audio it means pulse-width modulation i.e. the audio signal is carried by pulse width rather than voltage level, so it is still an analogue signal even when generated via digital means. There are only two levels: maximum + and maximum -, corresponding to the supply rail voltages.

For radio Class D seems to mean any switching type power amp which is not clearly Class E or F or whatever.
Thanks for clarifying those points - here's what I was thinking of with Class D

https://upload.wikimedia.org/wikiped...wm_amp.svg.png
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Old 9th Jan 2019, 1:36 pm   #12
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Default Re: Origin of Class-A, Class-B etc.

Yes, that is Class D.
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Old 9th Jan 2019, 2:35 pm   #13
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Default Re: Origin of Class-A, Class-B etc.

Quote:
Originally Posted by G6Tanuki View Post
I've always been fascinated by "Quiescent-push-pull" as used in 1930s battery radios.

Sort-of Class-B2, intended to save HT-current but because the grids of the P-P stage drew significant grid-current you needed a beefy driver-stage whose demands generally offset the supposed benefits of the output-stage.
I thought it was the other way round - that QPP was Class B1 (or maybe even AB1 and 1930's 'Class B' was actually B2 - with grid current?
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Old 9th Jan 2019, 9:28 pm   #14
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Default Re: Origin of Class-A, Class-B etc.

Quote:
Originally Posted by kalee20 View Post
I thought it was the other way round - that QPP was Class B1 (or maybe even AB1 and 1930's 'Class B' was actually B2 - with grid current?
Yes, you're right: see http://www.r-type.org/addtext/add019.htm

The downside of both approaches - for battery valves at least - seems to have been that they still needed an extra driver-valve with its associated HT/LT drain.

One isea I always liked was the "Sliding-bias" amplifier approach - where the bias (and so the standing current in the output valve(s)) was varied in accordance with the amplitude of the signal at the time. This could be done either by varying the control-grid bias, or in the case of tetrodes/pentodes by varying the screen-grid using a 'clamp' valve.

Sometimes strangely called "Class K" operation - see http://www.813am.qsl.br/artigos/modu..._cq_sep_54.pdf

or "Bias-shift/Reference-shift" operation - the example I remember uses a single-ended 6L6 as the modulator and gets 30-or-so Watts of audio at peaks. It's very much like an audio version of the "series-gate" controlled-carrier approach used by some Heathkit transmitters.
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Old 9th Jan 2019, 9:42 pm   #15
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Default Re: Origin of Class-A, Class-B etc.

I'm still trying to track down the origin of class-A, class-B, etc and still not having too much luck.

By scanning through lots of Wireless Worlds (who I would have thought would have published articles on the classification of amplifiers), in 1933 and 1934 class B push-pull was mentioned lots of times as it was the new way of getting more output from a battery-powered radio without incurring too much quiescent current. QPP is touted as another way.

What we would call class A amplifiers (ie single-ended, constant current) are simply called 'normal' or 'standard' amplifiers. As far as I can see, in the 1930s WW never calls them class A - what did they think came before class B?

I still have a lot of WWs to get through at https://www.americanradiohistory.com...d_Magazine.htm but so far the first mention of class A is in the December 1954 issue.

As mentioned in the posts, the radio handbooks describe the classes, but don't give an origin.
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Old 9th Jan 2019, 9:54 pm   #16
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Default Re: Origin of Class-A, Class-B etc.

Class A output stage is mentioned in W.W. certainly as far back as 1933.

Lawrence.
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Old 9th Jan 2019, 10:39 pm   #17
saddlestone-man
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Default Re: Origin of Class-A, Class-B etc.

Hi Lawrence

Do you know which issue of WW in 1933 you've seen this?

Best rgds. Stef
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Old 9th Jan 2019, 11:14 pm   #18
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Default Re: Origin of Class-A, Class-B etc.

Mag. page 519 "New LF Systems in America":

https://www.americanradiohistory.com...ld-1932-12.pdf

Here's the ref. to one of my earlier posts about the I.R.E reference c1933, the RCA Radiotron Manual RC11 (1933)...Page 9...2nd para:

http://www.nj7p.org/Manuals/PDFs/Tub...RC-11-1933.pdf

Lawrence.
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Old 9th Jan 2019, 11:42 pm   #19
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Default Re: Origin of Class-A, Class-B etc.

Here's the chapters on Push-Pull and Class B amps from John Scott-Taggart's "The Manual of Modern Radio", published 1933. While it does refer to both Class A and Class B, the only use of the expression "Class A" ( actually ' Class "A" ') is in the section "Dictionary of Technical Terms". The expression is never used anywhere else. From the mention in the introduction to Chapter 15, "Recent Developments" of "Until the last year or two...", it seems that the expression "Class B" (and by inference, "Class A") had only just become popular, which would date their introduction (in the UK at least) as circa 1931-32.
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File Type: pdf Man Mod Rad 1933.pdf (1.22 MB, 42 views)
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Old 10th Jan 2019, 1:03 pm   #20
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Default Re: Origin of Class-A, Class-B etc.

Many thanks to Lawrence and Emeritus for the early references, very much helping to pin down the date of amplifier classification. I'll take a look through WWs for 1931-32 to see if its recorded there.
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