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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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6th Jan 2019, 6:41 pm | #1 |
Hexode
Join Date: Mar 2009
Location: Cirencester, Gloucestershire, UK.
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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. |
6th Jan 2019, 6:51 pm | #2 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
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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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6th Jan 2019, 9:00 pm | #3 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
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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. |
6th Jan 2019, 9:01 pm | #4 |
Dekatron
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Location: Leominster, Herefordshire, UK.
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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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8th Jan 2019, 1:00 pm | #5 |
Heptode
Join Date: Jul 2010
Location: Wellington, New Zealand.
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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'. |
8th Jan 2019, 1:02 pm | #6 |
Heptode
Join Date: Jul 2010
Location: Wellington, New Zealand.
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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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8th Jan 2019, 1:20 pm | #7 |
Nonode
Join Date: Nov 2016
Location: Aberaeron, Ceredigion, Wales, UK.
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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.
Cheers John |
8th Jan 2019, 2:24 pm | #8 | |||
Rest in Peace
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Re: Origin of Class-A, Class-B etc.
Quote:
Quote:
Quote:
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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8th Jan 2019, 3:20 pm | #9 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
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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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8th Jan 2019, 7:06 pm | #10 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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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. |
9th Jan 2019, 12:57 pm | #11 | ||
Heptode
Join Date: Jul 2010
Location: Wellington, New Zealand.
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Re: Origin of Class-A, Class-B etc.
Quote:
https://upload.wikimedia.org/wikiped...wm_amp.svg.png |
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9th Jan 2019, 1:36 pm | #12 |
Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
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Re: Origin of Class-A, Class-B etc.
Yes, that is Class D.
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9th Jan 2019, 2:35 pm | #13 | |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
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Re: Origin of Class-A, Class-B etc.
Quote:
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9th Jan 2019, 9:28 pm | #14 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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Re: Origin of Class-A, Class-B etc.
Quote:
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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9th Jan 2019, 9:42 pm | #15 |
Hexode
Join Date: Mar 2009
Location: Cirencester, Gloucestershire, UK.
Posts: 391
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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. |
9th Jan 2019, 9:54 pm | #16 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
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Re: Origin of Class-A, Class-B etc.
Class A output stage is mentioned in W.W. certainly as far back as 1933.
Lawrence. |
9th Jan 2019, 10:39 pm | #17 |
Hexode
Join Date: Mar 2009
Location: Cirencester, Gloucestershire, UK.
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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 |
9th Jan 2019, 11:14 pm | #18 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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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. |
9th Jan 2019, 11:42 pm | #19 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
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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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10th Jan 2019, 1:03 pm | #20 |
Hexode
Join Date: Mar 2009
Location: Cirencester, Gloucestershire, UK.
Posts: 391
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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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