Hello!
I hope someone can help me.
I'm playing around with some tube circuits because this is my first tube project. I want to build an preamplifier and therefore I'm trying some circuits using my pspice.
Now I want to construct a cascode by using the ECC81 tube. But the results a very bad.
Can anyopne explain me how to setup the the resistor values by using the ECC81? I've found some examples on the web but in this examples there are used other triodes and they don't explain why to use this value and so on.
My on experiments following the description on valvewizard.co.uk doesn't succeed.
By searching and reading here I found a hint that Morgan Jones gives an example of a cascode based on the ECC81 in his great book. He points out to use high voltages (+400V) to get good results. Unfortunately I don't have this book an d it is not easy to get it here in Germany. So is there anybody who owns this book and can tell me something aboiut the cascode or can scan the schematic and mail it to me? That would be nice!
Greetings,
Raphael
I hope someone can help me.
I'm playing around with some tube circuits because this is my first tube project. I want to build an preamplifier and therefore I'm trying some circuits using my pspice.
Now I want to construct a cascode by using the ECC81 tube. But the results a very bad.
Can anyopne explain me how to setup the the resistor values by using the ECC81? I've found some examples on the web but in this examples there are used other triodes and they don't explain why to use this value and so on.
My on experiments following the description on valvewizard.co.uk doesn't succeed.
By searching and reading here I found a hint that Morgan Jones gives an example of a cascode based on the ECC81 in his great book. He points out to use high voltages (+400V) to get good results. Unfortunately I don't have this book an d it is not easy to get it here in Germany. So is there anybody who owns this book and can tell me something aboiut the cascode or can scan the schematic and mail it to me? That would be nice!
Greetings,
Raphael
Hi Audio Angel
You are wrong .
It's not difficult to get the Morgan Jones book !!
Even if you are in Germany !!!
Try www.amazon.com !!!
Regards ,
Carlos
You are wrong .
It's not difficult to get the Morgan Jones book !!
Even if you are in Germany !!!
Try www.amazon.com !!!
Regards ,
Carlos
It is really funny. Instead of an explanation how a cascode has to be constructed I got more hints to buy this book. Buying a second hand book from Amazon I would have to pay more money than for a new book because of the shipping costs to Germany.
So let us go back to the original question: How to setup up a cascode using the ECC81.
Greetings,
Raphael
So let us go back to the original question: How to setup up a cascode using the ECC81.
Greetings,
Raphael
AudioAngel said:
So I thought your original question was specifically about the book and its content. It's really not that funny.
If you're interested in setting up a cascode using the ECC81, then you should try a cheaper and readily available book (at least to you) by Rainer zur Linde: Build Your Own AF Valve Amplifiers (published in 1997 by Elektor Electronics). On page 98 you'll find a cascoded ECC81.
Regards,
Milan
Hi Raphael,
To build a cascode properly and explain it is a little beyond a post or two. You have the general idea it seems. What you haven't told us is how much B+ you have, your signal levels and gain. We also don't know how much noise and distortion is acceptable, I'll guess you want to minimize those.
One of your problems may be the heater to cathode voltage breakdown rating also. Mr. ECC88 was designed for this purpose in mind.
So give use some expected values to work with at least. What you asked was similar to saying, "I want you to design a car, with four doors using these tires".
-Chris
To which Milan posted ....
I'd like to add that I think we all have his book it seems.
To build a cascode properly and explain it is a little beyond a post or two. You have the general idea it seems. What you haven't told us is how much B+ you have, your signal levels and gain. We also don't know how much noise and distortion is acceptable, I'll guess you want to minimize those.
One of your problems may be the heater to cathode voltage breakdown rating also. Mr. ECC88 was designed for this purpose in mind.
So give use some expected values to work with at least. What you asked was similar to saying, "I want you to design a car, with four doors using these tires".
-Chris
Ok, some background information.
One or two years ago I saw a preamp schematic build with a cascode of ECC81. Unfourtunaly I ignored it because I was not thinking about a tube preamp at this time. Now I want to go with tubes and want to drive my Aleph-Xs with a tube preamp. So the cascode returned to my mind. After reading some stuff about cascodes I thought it would be a good starting point because of its low noise and distortion.
Coming to the tech specs:
After reading some stuff designing a tube cascode seems to me more like choosing the correct values for the resistors by the tube datas and then looking which gain and so on the cascode will have. Therefore I want to go like this: Choosing the best performance values for resistors and voltages and after that doing the next step in designing the rest of the preamp.
But in the meantime Reinhard told me that a cascode is not a really good choice for a preamp because of its PSRR. However my nosiness is still there and I want to know how to construct a ECC81 cascode.
Raphael
One or two years ago I saw a preamp schematic build with a cascode of ECC81. Unfourtunaly I ignored it because I was not thinking about a tube preamp at this time. Now I want to go with tubes and want to drive my Aleph-Xs with a tube preamp. So the cascode returned to my mind. After reading some stuff about cascodes I thought it would be a good starting point because of its low noise and distortion.
Coming to the tech specs:
After reading some stuff designing a tube cascode seems to me more like choosing the correct values for the resistors by the tube datas and then looking which gain and so on the cascode will have. Therefore I want to go like this: Choosing the best performance values for resistors and voltages and after that doing the next step in designing the rest of the preamp.
But in the meantime Reinhard told me that a cascode is not a really good choice for a preamp because of its PSRR. However my nosiness is still there and I want to know how to construct a ECC81 cascode.
Raphael
A cascode is useful when you want to minimize Miller capacitance. For most preamp use (input stage of phono excepted), this is generally not a major problem. The cascode's disadvantages (need for separate heater supplies, poor PSR, high output Z) far outweigh its advantages for most applications.
You can get as good or better distortion performance from the same tube configured as a common cathode amplifier and still have a section left to use as a cathode follower, knocking down the source Z very nicely while retaining the PSR advantages.
You can get as good or better distortion performance from the same tube configured as a common cathode amplifier and still have a section left to use as a cathode follower, knocking down the source Z very nicely while retaining the PSR advantages.
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