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Old 5th October 2005, 01:53 AM   #11
ilimzn is offline ilimzn  Croatia
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That would work just exactly the same with the bypassed part of the cathode resistor replaced with a short, and the grid leak grounded. Apparently, whoever designed it, was unsure how to bias a CF...
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Old 5th October 2005, 01:08 PM   #12
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Tyimo,

What's the sensitivity of the power amp for full O/P? I'm thinking of a different approach.

If less than 2 V. RMS will drive the power amp into clipping, you don't need any gain at all and a buffered level control would be FINE. Wire the triode as a cathode follower with the pentode wired up as a constant current sink for the CF's load.
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Old 5th October 2005, 05:15 PM   #13
Tyimo is offline Tyimo  Hungary
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Hi!
Thanks to all! Very intersting discussion!


Quote:
Wire the triode as a cathode follower with the pentode wired up as a constant current sink for the CF's load.
Eli Duttman: My main power amp need 2-2.5V or a bit more input, but I like the idea you writen. I could try it with another amp what needs only 1.5V for full output. Could you post here a schematic?

Greets:

Tyimo
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Old 5th October 2005, 06:01 PM   #14
ilimzn is offline ilimzn  Croatia
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Quote:
Originally posted by Tubes4e4
[B]Hi,
one should consider that the pentode section of ECL82/6BM8/PCL82/16A8, when being triode strapped, is not a particulary linear one. Have a look at:

http://www.tubes.mynetcologne.de/roe..._as_triode.pdf

This might be relativated by the small signal swing needed for a preamp output.
Just looked at it and you are right, of course. Seems like the only way to get decent linearity is to use a CCS plate load, which complicates things. OTOH, the gain would be low (mu is about 8 IIRC) and an unbypassed cathode resistor would make it lower still (at the expense of output impedance, though). For a couple of V RMS it may still have decent enough distorsion specs even without these extra measures.
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Old 5th October 2005, 06:15 PM   #15
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Tyimo,

The highly linear buffer could be used with your main power amp if a 1:2 step up microphone transformer is used at its I/P.

Steve Eddy is EXPERT at using mic. trafos with buffers. I'll try to have him post in this thread.
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Old 6th October 2005, 03:04 AM   #16
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Quote:
Originally posted by Eli Duttman
The highly linear buffer could be used with your main power amp if a 1:2 step up microphone transformer is used at its I/P.

Steve Eddy is EXPERT at using mic. trafos with buffers. I'll try to have him post in this thread.
Hey Eli!

I just sent you a reply to your EMail.

Actualy I'd probably recommend using the 1:2 at the input of the amp depending on your buffer's output impedance and whether it can drive a 1.5k ohm load.

I'm often reluctant to recommend using those 1:2 mic trannies except where one has control over what's driving it as their 1.5k ohm input impedance (when they're properly loaded) will cause some output stages to choke. You know, like most tube output stages.

se
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Old 6th May 2006, 06:33 AM   #17
Tyimo is offline Tyimo  Hungary
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Hi! I am back again. :-)

The situation is changed, my new power amp need 15 V input and has 330K Zin. (it is a mosfet follower). Mostly I use it with CDplayer which has more than 2 V output.

So, I would like to ask the Tube Gurus to suggest me a good preamp with ECL82 tube.

Until now I found 2 design and I would like to hear (read) your oppinions.

Here is the first competitor:
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File Type: jpg pre_ecl82-6bm8.jpg (22.2 KB, 381 views)
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Old 6th May 2006, 06:35 AM   #18
Tyimo is offline Tyimo  Hungary
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and the next one:
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File Type: gif eclo82head.gif (5.9 KB, 380 views)
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