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Old 17th November 2006, 02:02 PM   #11
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Many of the popular vacuum tube circuits have their roots in 1950's design. They are simple and work reasonably well when constructed with modern components. Make sure that you understand these designs before attempting anything more complex.

There is a large element of vacuum tube audiophiles that are resistant to change. Some of this is due to strong opinions voiced on other audio forums where new ideas that challenge the thinking of a few "gurus" is shunned. Some is also because of a lack of understanding of modern engineering and modelling tools. I see the same thing happening in big technology corporations. New ideas are often shunned because they force too many people to think in ways that they haven't done regardless of the circuitry or technology involved.

There is not much literature out there with new vacuum tube technology because there hasn't been any significant development work done in this area since the late 60's. The basics still hasn't changed. The popular old books will still teach you how a vacuum tube works. Study the Radiotron Designers Handbook, 4th edition. You can find the entire book available for download on the web.

Look here for this and other technical books:

http://www.pmillett.com/technical_books_online.htm

I have also found that engineering textbooks from the 1950's are also full of all of the vacuum tube technology that you would ever need. I have a book from MIT that is 80% advanced Calculus applied to vacuum tubes.

The Morgan Jones books are also good sources of old vacuum tube fundamentals from a modern perspective.

Once you understand the fundamentals of how tubes and the associated circuitry work, you can apply your engineering knowledge to them. There is no reason that you (or any other engineer) can't experiment and devise new topologies that use vacuum tubes alone, or with other modern components. Just don't expect any new circuitry to be adopted by the vacuum tube community overnight.

I published my PowerDrive circuit 3 years ago. It was immediately blasted in those other forums, and directly to me in e-mail. ALL of this criticism came from people who NEVER tried the circuit. I even got an e-mail saying that I should change my name from Tubelab to Transistorlab. As time went by a few brave souls actually tried the PowerDrive circuit, and liked it. They were vocal enough that more people tried it. I don't get hate mail any more, but most main stream tube audiophiles will never accept the circuit because it contains a MOSFET follower in the signal path.

A solid state device can be used with a vacuum tube, if careful thought is applied. True a transistor (or other device) can be very nonlinear if used as a gain stage. I don't think that there are too many people advocating this. There is no reason that a semiconductor can't be used as a buffer, or control loop (outside the audio path). If you do this you must understand that the solid state devices come up instantly, and vacuum tubes come up slowly. All operating conditions must be considered when mixing the two in the same circuit.

The following sites may be of some interest to those that are open to new ways of thinking with vacuum tubes. Keep in mind that some of the circuits on these sites may exist in the authors mind only. Some of them do not work, I have found this out by trying. If you want to design some new vacuum tube science, please share it with us, and be prepared to fry a few parts. Experiment on cheap stuff at first, and understand the safety precautions involved with high voltages.

www.tubecad.com Some circuits are just concepts, some do not work, some work excellent, the software works good, but is limited to single stages. The Akido circuitry is an example of new thinking applied to old vacuum tubes. I have not heard anyone say bad things about this design. I bought his boards, and built them. They do work well.

www.pmillett.com Many old books, some new tech, plenty interesting reading.

http://members.aol.com/sbench101/ No new information in a few years, but several circuits that no one else would try. Yes, new vacuum tube topologies. Some of them actually work!

www.tubelab.com My site. A few circuits, designs, and concepts. The ones that are labled "circuit concepts and ideas" have not been tested, and the stuff that isn't quite ready for prime time is labeled as such. New material is being added slowly. I have a full time engineering job.
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Old 20th November 2006, 10:41 AM   #12
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Thank you very much for youe excellent explanations.

I'm checking out a couple of books, they are very interesting thought.

Thanks.


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Old 20th November 2006, 08:44 PM   #13
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Very interesting thread, I have learned a few new things here already.

TUBELAB I visited your site and I must say I am impressed. I would like to build a SE amp later this year or early next year.

I would like to build an amp based on TS 5881 or 6V6GT power tubes. The main reason is that I have a boatload of both of those tubes. The other option might be TS 7027A or Phillips 7581A power tubes.

I have been building Tube Guitar Amps for about 9 or 10 years but have never attempted anything Hi FI before. This should be a good learining expierence for me.

I will contact you when I am ready to build.
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Old 21st November 2006, 05:23 AM   #14
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Default Re: about newbies...and textbook..

Quote:
Originally posted by Stefanoo
Is there any new thing on the valves design NOW (i'm talking about the last 15-20 years) that wasn't still discovered by then?
I'm not saying that it's not possible, but you have to remember that this particular technology is about 80 years old now. Just about every possible connection (common cathode, common grid, common plate connections, using the control grid as the output and the plate as input, the various triode connections, and stacked topologies (cascode, SRPP, Mu stage) has been done a long time ago. There are lots of ideosyncratic designs for specific purposes the "phasetron" and CRT FM modulators, tubes for generating SSB, frequency conversion, FM demodualtion, and even analog to digital conversion have all been done already. If there are any unknown tricks that haven't been tried before, I sure haven't heard of any.

Quote:

The modern valve equipments are still using the same schematics developed in the 50's -60's or even erlier (40's) ?
Yes. However, most of the solid state audio amps are also using the same circuits, just modified for silicon. Having PNP as well as NPN devices simplifies the ciruits a bit (no phase inverters required) and the high current/low voltage nature of SS makes it a helluvalot easier to implement OTL topologies, but the basic circuits aren't all that much different.

Quote:

That is a question that i think most of the newbies would put to themeselves....because.....you see this source of information and you wonder if you have to study them or you have drop or skip them to pass for a better up-to-date source!
Often, there aren't any, and the information in something like the Radiotron Designers Handbook is just as valid today as it was when it was hot off the presses. In many cases, it's probably better since it wasn't written after so much misinformation started appearing.

Quote:
Many of the popular vacuum tube circuits have their roots in 1950's design. They are simple and work reasonably well when constructed with modern components. Make sure that you understand these designs before attempting anything more complex.
Don't necessarily believe everything you read. By the 1950s, the "numbers game" was well underway. Here, you see recommendations for the use of extreme gNFB. Using huge amounts of gNFB does make the distortion figures look good to please marketing departments, but not ears. Unless the basic design is badly flawed, there is no way that you'd ever need 20+db(v) of gNFB. Also, always remember that the designs for "Big Box" systems were driven by the bottom line, not sonic excellence.

The A Number One improvement hasn't come from doing anything radically new, but due to having at our disposal improved technologies. New line and interstage xfmrs using exotic core materials that didn't exist in the 1930s allow for much better performance from 1930s circuits than were ever possible in the 1930s. There have also been vast improvements in passive components. No longer do you have to deal with leaky (in the electrical sense) foil and wax paper capacitors. Modern capacitors using the latest dielectrics simply are more reliable, and create much less distortion. Metal film resistors are quieter than the old carbon comps, and more stable as well. With solid state, you can build much better CCSs and voltage regulators. SS makes it very easy to use DC heater power for quieter operation and fewer IMD products since filament hum is no longer a problem. SS power supplies offer better regulation, even if active regulators aren't used. Power MOSFETs make for much better drivers for operating Class A2 or AB2, and makes such operation more feasible than it would be otherwise.

Novelty for the sake of novelty seldom makes for any real improvement, and often has the opposite effect.
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Old 21st November 2006, 06:12 AM   #15
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this is also a nice explanation.

thanks.


Stefano.
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Old 21st November 2006, 07:11 AM   #16
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Sorry...just a question:

the tubecad's website is basically a collection of articles.
Is it also a periodic?
What i see on the website is all i can find as tubecad journal....or it's possible to buy it somehow!?

is there any periodic journal on valves, an interesting one, that i could buy?
(like audioexpress....ect...)

thanks
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