You might be interested to know that I have just opened a Wireless World archive page on my website. The articles are old enough to be out of copyright, and so inevitably are focused on valve technology. The first item is a 1957 article on transformerless valve amplifiers.
See it here: The Wireless World Archive
.
See it here: The Wireless World Archive
.
Valves, Douglas? Impressions gained from reading your own articles in the same Wireless organ left me with the impression that you regarded the thermionic FET as a plaguey anachronism -doomed to a well-earned extinction ere the Millennium turned.
Or have the intervening years softened your heart. Can we expect articles on squeezing the most out of a 2A3, supported by transistor current sources and new ingenuities?
Or have the intervening years softened your heart. Can we expect articles on squeezing the most out of a 2A3, supported by transistor current sources and new ingenuities?
Softened my heart? You must have the wrong bloke. I think valves are an expensive, inefficient, unreliable, noisy, non-linear and potentially dangerous way to make an amplifier, but apart from that I have nothing against them.
Having said that, I think any bit of amplification technology can be interesting, eg:
Electro-Mechanical amplifiers
or even:
Mechanical Amplifiers.
I am just about to upload a valve amplifier design by Peter Baxandall. Anything written by Peter is worth reading.
I think designers of valve gear are profitable, experienced, and brave people.
And we know that valves are more linear, in terms of Organic Nature that is dynamic, and all major laws are of the 2'nd order... Well, decay of sounds is exponential, but opamps spoil it anyway.
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I have just uploaded a Class-A valve amplifier design by Peter Baxandall. I am hardly qualified to judge, but it seems a neat design, explained with impeccable clarity. I would be glad to hear any comments on the design.
See here: The Amplifier Institute.
The input sensitivity is quoted as 4 Vrms for 5 Watts out into 8 Ohms, which seems to me to be exceptionally insensitive. What would be 'normal' for this sort of amplifier?
See here: The Amplifier Institute.
The input sensitivity is quoted as 4 Vrms for 5 Watts out into 8 Ohms, which seems to me to be exceptionally insensitive. What would be 'normal' for this sort of amplifier?
Is it a joke, Doug? I see some scanned text about transistors and Miller compensation, under your own books...
The design presented (it's here, Anatolij!) The Wireless World Archive
is notable for a couple of things.
Unlike many published valve amp designs, the author has gone to extreme lengths to present a design that will perform and sound closely, from sample-to-sample.
Exact construction of the output transformer is a prime example, there would be no excuse for deviating from the author's intentions.
It's very conservative, running EL84s at 9W anode burn, which is rarely done in DIY, and never done in commercial amps, which frequently run them at over 100% of ratings. And 5W from a topology that usually has 15W squeezed from it.
A very notable remark in the text is the admission that applying global NFB to a valve output amplifier (where the open loop distortion is overwhelmingly 2nd Harm) will introduce higher harmonics. The loop feedback is then added anyway! O, well. Keeps sample-to-sample variation at bay.
is notable for a couple of things.
Unlike many published valve amp designs, the author has gone to extreme lengths to present a design that will perform and sound closely, from sample-to-sample.
Exact construction of the output transformer is a prime example, there would be no excuse for deviating from the author's intentions.
It's very conservative, running EL84s at 9W anode burn, which is rarely done in DIY, and never done in commercial amps, which frequently run them at over 100% of ratings. And 5W from a topology that usually has 15W squeezed from it.
A very notable remark in the text is the admission that applying global NFB to a valve output amplifier (where the open loop distortion is overwhelmingly 2nd Harm) will introduce higher harmonics. The loop feedback is then added anyway! O, well. Keeps sample-to-sample variation at bay.
Ah, I see. It is under still the same link, with Wireless World scans.
Our forum members today design much better amps.
Looks like Peter Baxandall did not think yet back in 1957 about Miller capacitances, and did not share my belief that class A push-pull amp is suboptimal. And he did not think about nested feedbacks...
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