The Wireless World Archive
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Page opened: 31 Jan 2011 |
THE WILLIAMSON HIGH-QUALITY AMPLIFIER: Apr 1947
D T N Williamson
This amplifier was widely regarded as the best design available for home construction at the time. However there were persistent reports that it was unduly prone to high-frequency instability.
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HIGH-QUALITY AMPLIFIER DESIGN: Jan 1948
Peter Baxandall
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BASS WITHOUT BIG BAFFLES: Apr 1951
K A Exley
The idea is to generate a "synthetic bass" by adding distortion to the audio frequencies below 100 Hz, the statement being made that this increases the subjective volume of the fundamental. WW was already much occupied with "high-fidelity" at this time, and the idea of adding extra distortion- because valve amplifiers already produced plenty- was not enthusiatically received by the majority of readers.
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NEGATIVE-FEEDBACK TONE-CONTROL: Oct 1952
Peter J Baxandall
The famous Baxandall tone-control article. Note that the original version used a treble pot with a centre-tap; the simpler version universally adopted omits this. The resulting standard Baxandall circuit has some interesting subtleties regarding its input impedances, which can be much lower than a quick inspection of the circuit suggests; these effects described in my slim monograph: Small Signal Audio Design
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FRICTIONAL-DRIVE LOUDSPEAKERS: January 1953
Anon
An unconventional loudspeaker is described with an amplifier that converts electrical signals into mechanical forces by voltage-controlled friction. Electrical power was needed both to run a carbon microphone and polarise the frictional element, but this could be provided by a dynamo attached to the same hand-crank that worked the frictional element. This surely must have been developed with nuclear war in mind.
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HOME-MADE TRANSISTORS: January 1954
P B Helsdon
This remarkable article shows you how to make your own point-contact transistors by taking the innards of a germanium rectifier and adding two 'cat's-whiskers'to it. The point-contact transistor was the first type made, and it was not very satisfactory, having poor performance and being both delicate and unreliable. When the much-superior junction transistors (the type we use today) came along the point-contact version disappeared rapidly. Not even the most die-hard retro-audio enthusiast has asked for it to be brought back.
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INEXPENSIVE 10W AMPLIFIER: August 1954
Author unknown (WW staff?)
HIGH-QUALITY SOUND REPRODUCER: Sept 1954
Author unknown (WW staff?)
STYLUS IN WONDERLAND: Oct 1954
O J Russell
INEXPENSIVE 10W AMPLIFIER COMMENTS: Oct 1954 and Dec 1954
GRAMOPHONE & MICROPHONE PRE-AMPLIFIER: January, February 1955
Peter Baxandall
A fairly complex design, using five valves. This is the preamplifier referred to in the "Inexpensive High-Quality Amplifier" article of March 1957.
I'm afraid the scanning is not wholly satisfactory as the volume has been bound so the extreme right text is not visible on every other page.
400W POWER AMPLIFIER: Nov 1955
G R Woodville
A seriously powerful amplifier by valve standards, with ten KT88s in parallel push-pull.
TETRODES WITH SCREEN FEEDBACK: Jan 1956
Author unknown (WW staff?)
A review of the so-called Ultra-Linear output stage for valve amplifiers. It was controversial when first introduced.
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ULTRA-LINEAR OUTPUT TRANFORMERS: Jan 1956
D M Leakey & R M Gilson
An article focusing on possible stability problems in ultra-linear output stage valve amplifiers.
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DISTORTION IN ELECTROSTATIC LOUDSPEAKERS: Feb 1956
Author unknown (WW staff?)
A short note on the non-linearity and stability of electrostatic speaker diaphragms, pointing out that some sort of resistive rather than metallic coating is required, to prevent charge migration.
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LOOPS WITHIN LOOPS: Feb 1956
'Cathode Ray'
'Cathode Ray' was the pseudonym of M G Scroggie. (1901 - 1989) He contributed more than 800 articles to Wireless World. One might have expected him to be joined by Anode Arnold and Sid The Grid, but mercifully this never actually happened.
PHASE SHIFT AND SOUND QUALITY: Apr 1956
James Moir
A careful examination of the audibility of phase shift by the well-respected James Moir. He concludes that the amount of phase-shift you are likely to get in an amplifier- and he was of course talking about valve amplifiers with output transformers- is completely inaudible. More modern studies confirm this, and the article is as valid today as when it was written.
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CASCODE AF AMPLIFIER: June 1956
L B Hedge
A cascode valve amplifier using a "long-tailed cascode pair" as combined preamplifier and phase-splitter. Apparently a patent was applied for, but the idea does not seem to have prospered.
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CHARACTERISTICS OF FIXED RESISTORS: June 1956
G W A Dummer
This article is a collection of information on carbon-composition resistors. Since their use nowadays is confined to a few specialist niches, data is hard to come by. What we have here could be useful.
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MORE ABOUT NOISE: June 1956
'Cathode ray'
An interesting examination of some complications affecting the calculation of Johnson noise in resistors.
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INEXPENSIVE VARIABLE SLOPE FILTER: Nov 1956
D M Leakey
DISC RECORDING CHARACTERISTICS: Nov 1956
J D Smith
Up to 1955 a great variety of equalisation curves for disc cutting and replay were in use. It was common for a preamplifier to have four or more switchable equalisation options for disc replay, selected according to the company who had made the record you were playing. In 1955 the USA standardised on what became known as RIAA equalisation, and the same standard was adopted in the UK as BS1928/1955. This came as a great relief to all concerned.
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OUTPUT TRANSFORMERLESS AMPLIFIERS: Feb 1957
Author unknown (WW staff?)
A review of the tricky business of making valve amplifiers without output transformers. One of the most powerful motivations was that it would allow much more negative feedback to be applied, because there would be no phase-shift caused by an output transformer.
INEXPENSIVE HIGH-QUALITY AMPLIFIER: March, April 1957
Peter Baxandall
A 5W Class-A valve amplifier, published in two parts. Written with Peter's usual clarity of style.
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THE 88-50 POWER-AMPLIFIER: April 1957
W Heath & G Woodville
This 50W power amplifier used the relatively new KT88 (KT standing for 'kinkless tetrode') output valve which is described as a 'pentode', though it is actuually a beam tetrode. The supply rail is at an intimidating +500V.
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INEXPENSIVE PRE-AMPLIFIER: May 1957
Peter Baxandall
A much simpler design than the 1955 preamplifier, using two valves, or rather one double-triode. (ECC81) It was designed to feed the "Inexpensive High-Quality Amplifier" article of March 1957, and so has the high output level of 4 Vrms.
THE 88-50 PREAMPLIFIER: July 1957
W Heath & D M Leakey
This preamplifier partners the 88-50 power amplifier published in April 1957; that article is available just above. It use two pentodes and a double triode. The article describes the design decisions taken in detail.
MULTI-VALVE CATHODE FOLLOWERS Part 1: July 1957
J G Thomason
This article was written in the days when adding an extra active device was a serious matter because the cost was high.
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MULTI-VALVE CATHODE FOLLOWERS Part 2: Aug 1957
J G Thomason
This article was
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HOW LITTLE DISTORTION CAN WE HEAR?: Sept 1957
M Lazenby
Ear distortion and masking effects
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| This article references some classic research on the subject. |
MORE TRANSFORMERLESS AMPLIFIERS: Mar 1958
Author unknown (WW staff?)
A follow-up to the February 1957 article above.
DC-COUPLED TRANSISTOR AUDIO AMPLIFIER: May 1958
D A G Tait
This is one of the earliest designs for a transistor power amplifier that appeared in WW. It is a three-transistor circuit in single-ended Class-A, with shunt feedback. The DC standing current of the output stage passes through the coil of the loudspeaker, which I would have thought would made its already mediocre linearity a good deal worse, though the author states it will not be 'troublesome'. Even allowing for the date, this seems to be a rather crude design. No distortion figures are given.
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THE BOOTSTRAP FOLLOWER: Jan 1961
G W Short
A close examination of the properties of the cathode follower and variations thereon.
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ACCURATE RECORD EQUALISER: Mar 1961
T M A Lewis
Semi-passive RIAA is not a new idea. Here the LF part of the RIAA characteristic is implemented by frequency-dependent series feedback, while the HF roll-off is done by a passive RDC network after the two-transistor amplifier.
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LOW-COST STEREO AMPLIFIER Part 1: Apr 1961
E Jeffery
Two-parter describing a 9W + 9W stereo valve power amplifier
LOW-COST STEREO AMPLIFIER Part 2: May 1961
E Jeffery
Two-parter describing a 9W + 9W stereo valve power amplifier
TRANSISTOR AUDIO POWER AMPLIFIER: Nov 1961
R Tobey & J Dinsdale
This article is one of the milestones of power amplifier design in WW. It is one of the first designs to look like what we would call a modern power amplifier.
TRANSISTOR HIGH-FIDELITY PRE-AMPLIFIER: Dec 1961
R Tobey & J Dinsdale
A preamplifier designed by Tobey & Dinsdale to complement their power amplifier of November 1961.
SLIDING-BIAS AMPLIFIERS: May 1962 NEW
Thomas Roddam
Sliding-bias operation uses a Class-A amplifier with a quiescent current that is controlled by the signal amplitude so that it increases when the output level is high, and falls back when it is low, to save power. The control signal is derived by peak-rectifying the input signal. This can obviously only operate in "oops- sorry" mode; in other words the start of every transient will be mangled as it takes a finite time for the quiescent current to be increased.
"UNBIASED": Oct 1963
by Free Grid
"Unbiased" was a commentary that appeared in Wireless World every month for almost 34 years.
It was written by 'Free Grid', the pseudonym of Norman Preston Vincer-Minter (?? - 1964). While the articles were often interesting, Free Grid had an unfortunate tendency to get bogged down in tedious etymological pedantry, as in the first section of this example.
While this is in many ways a typical contribution, what caught my eye was the reference to Klaus Fuchs in the second section, where an equation from one of his scientific papers was used as an example. Klaus Fuchs is far better known for having been one of the most notorious and damaging cold war spies; he was convicted in 1950. Surely both Free Grid and the Editor of WW would have realised who they were referring to? The cold war was very much still going on in 1963.Was Free Grid's choice of Fuchs' equation some sort of elaborate joke? I suspect so. |
RUMBLE CROSSFEED FILTERS
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