Cascode with ECC81(12AT7)=>Morgan Jones - diyAudio
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Old 23rd November 2006, 10:44 PM   #1
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Default Cascode with ECC81(12AT7)=>Morgan Jones

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
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Old 23rd November 2006, 11:25 PM   #2
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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
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Old 24th November 2006, 03:26 AM   #3
SY is offline SY  United States
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The ECC81 will work well as the top tube in a cascode. For the bottom, you might want to look at a tube that's happier working into a near-vertical load line, like an ECC88.

BTW, if memory serves, Morgan Jones didn't show an ECC81 in cascode in his book, just ECC88.
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Old 24th November 2006, 06:30 AM   #4
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Hello Raphael,

you can phone me under 05261 87586, have a CAD programm so we can design a cascode preamp in minutes.

Regards,
Reinhard
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Old 24th November 2006, 07:26 AM   #5
moamps is offline moamps  Croatia
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Quote:
Originally posted by SY
BTW, if memory serves, Morgan Jones didn't show an ECC81 in cascode in his book, just ECC88.
Yep. I'm looking at the book Valve Amplifiers (3rd edition) right now and there's no ECC81, just ECC88. BTW, a most excellent read!

Regards,
Milan
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Old 24th November 2006, 12:45 PM   #6
SY is offline SY  United States
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I think I nagged you to buy it...

Here's the money quote (invoking Fair Use):

Quote:
...the only general purpose valve that was designed to work well in a cascode is the ECC88/6DJ8 or E88CC/6922 (special quality version). Try other valves, by all means, but do not expect the performance to be as good.
(from Morgan Jones, Valve Amplifiers 3rd Edition, Newnes 2003)
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Old 24th November 2006, 01:46 PM   #7
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Try The Book Depository. I got both of Jones' books there cheaper than Amazon.
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Old 24th November 2006, 02:10 PM   #8
Jaap is online now Jaap  Netherlands
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Default ecc40 in cascode

Has anybody tried the ecc40 in a cascode ?
Did you like it ?
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Old 24th November 2006, 02:32 PM   #9
SY is offline SY  United States
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I haven't used an ECC40 but I have to say that it has absolutely the best documentation I've ever seen. All the discussion of microphony worries me a bit.
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Old 24th November 2006, 05:09 PM   #10
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If I am not mistaken Morgan Jones used cascoded ECC81's in a differential pair in a tube regulated power supply (as error amp).

"it was big, it was heavy, and it drifted because of the use of AC on the ECC81 heaters - the lm317 (maida) is rock stable"
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