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Old 15th January 2006, 11:09 PM   #41
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Default Comparison of different circuit designs

Anyone has a link talking about the characteristics, maybe even pros and cons of different types of circuit designs, for example, SRPP, common cathode, cascode, etc?

thanks!
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Old 23rd January 2006, 01:20 PM   #42
9am53 is offline 9am53  Canada
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Default tube testing

Hello, I have a question about tube testing. Whenever I look to buy tubes fro my guitar amps they give ratings like 120/122. What do these numbers mean?
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Old 23rd January 2006, 03:49 PM   #43
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Default Re: Comparison of different circuit designs

Quote:
Originally posted by pengboon
Anyone has a link talking about the characteristics, maybe even pros and cons of different types of circuit designs, for example, SRPP, common cathode, cascode, etc?
Every electronic boock wil explain the basis, especialy radio-electronic books. You must be able to loan some old radio-electronics book in a public library, and photocopy it. If you are lucky, the book will be from the time where tubes was king, and in almost all cases, they will be more complet as the new books.

With tubes, you have fondamentaly 3 basic circuits: common cathode, common grid and common anode. You have exactly the same with a transistor: common emiter, common base and common collector.

After, as with transistors, you have 3 class of operation: class A, B and C. With subclass as AB1 and AB2.

At the end, and again as with transistors, you can combine 2 or more tubes to archieve circuits as SRPP, cascode, PP, ...

Now, I cannot suggest a book that will explain all. One will be good to explain the basic circuits. another will have a good explaination for the classes of operation, one will be good to explain the cascode, one will be good to explain the noise. So you have to keep reading. And experiment. Radio electronics book are best for me because they are not so academic, but practical, and as you can find every possible circuit in radio-electronics, they are talking about a lot of things.

For me, the link to radau5.ch is the best I know with free reading. But it is personnal. Other can prefer other reading. Some book on radau have the equivalent circuits of each presented circuit. Those equivalent circuits are maybe the most important part of the book, because they show how the circuits work, and which formula you must use to calculate it.

You can take a look at
http://en.wikipedia.org/wiki/Categor...nic_amplifiers
The basic concepts are the same for tubes, the implementation is almost the same as with npn transistors, but the mathematics are not the same.
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Old 23rd January 2006, 03:52 PM   #44
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Default Re: tube testing

Quote:
Originally posted by 9am53
Hello, I have a question about tube testing. Whenever I look to buy tubes fro my guitar amps they give ratings like 120/122. What do these numbers mean?
Which amplifier is it? Which tube in the amplifier and what are the inscriptions on the tube?
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Old 24th January 2006, 05:50 PM   #45
9am53 is offline 9am53  Canada
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Hello, here is an example....
http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA%3AIT&rd=1
I just bought these but I dont really understand what the 120/117 and 122/120 things mean...
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Old 25th January 2006, 02:18 PM   #46
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I don't know. You must ask the seller.
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Old 25th January 2006, 04:20 PM   #47
9am53 is offline 9am53  Canada
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so when people test tudes and give these ratings you have to talk to the person who tested them to find out what the numbers mean? are you sure? I was under the impression that the numerator and denominator had specific meanings
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Old 25th January 2006, 08:12 PM   #48
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First, I was misunderstanding the question. I thinked at those number was the type of the tube.

Now, ratings or specifications are the result of some mesurment. A specification will have no meaning at all if we don't know the conditions of the mesurment. Another issue is at we must have an unity of mesure. 120/122 doesn't tell if we are speaking of cat, money or electric current.

As exemple for the conditions, if you look at Ia=f(Ua) for a triode, the manufacturer give you the conditions. It is for which grid voltages it have mesured the curves, and we can read 1 curve for each grid voltage. For a pentode, you will have one more condition, the screnn voltage, and we will get a full set of curves for each screen voltages.

Another exemple is the music power of an amplifier. In many cases, it doesn't tell anything because the manufacturer doesn't tell anything of the conditions of the mesurment.
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Old 26th January 2006, 02:16 PM   #49
9am53 is offline 9am53  Canada
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oh I see, so if they just tell me a bunchof numbers it doesnt realy mean anything...the guy said no leaking and something else...I hope they are ok...ahh well atleast I only paid 11 dollars for them including shipping...thanks!
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Old 6th February 2006, 02:04 PM   #50
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Back to the subject of this thread.

I found a copy of Vacuum Tube Amplifiers, by George E. Valley & Henry Wallman, McGraw-Hill, 1948. It is a very technical book that deal with every aspect of tube electronics. It is not really a book for beginner because I think at most beginners don't have enough mathematical knowledge to undestand it. But, it is a very interresting reading even for someone that doesn't have a good basic mathematical background.

It is a big book, around 750 pages, and it is in 2 pdf files, a little one with the preface and the contents, and a very big one (32398K) with the book. I can do a zip and put it somewhere on the internet, but I am not sure if it is legal. The book is copywrited, but it is from 1948, so I don't know if the copyright is still valid.

Can someone confirm if I can upload this book and will not get in trouble?
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