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PostPosted: 09 May 2010, 09:01 
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Joined: 14 Feb 2010, 13:13
Posts: 663
Location: Lisbon, Portugal
Hi!

I wonder what are the main differences on these 2 kinds of circuits, a Mu Follower and the Cascode.

They seem to be so similar.

What about performances?

Cheers,
Miguel


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PostPosted: 09 May 2010, 22:34 
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Joined: 08 Aug 2009, 03:11
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Location: Chilliwack, BC
Hi,

A cascode is different in that the output is taken off the top tube, which has an anode load resistor. Its advantage is it makes two triodes act like a pentode, hence lotsa gain and no Cmiller issues. Output impedance is quite high.

A mu follower has the top tube tied to B+ (The White CF being the exception) and the output taken off the top tube's cathode. Output impedance is low, but the maximum ideal theoretical gain is the mu of the bottom tube and it suffers from Cmiller.

Then you have a hybrid mu-follower. I did some experimenting with that here:
http://geek.scorpiorising.ca/hybridmu.html

Cheers!

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* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
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PostPosted: 12 May 2010, 15:39 
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Joined: 04 Jun 2008, 20:59
Posts: 4025
Location: Arizona, USA
Hi, You may also wish to checkout SRPP stages as they are similar. Gain is limited to the one (lower) section, but depending on the tube choice output impedance can be quite low (like with a 6DJ8). For ease of design I suggest the symetrical SRPP types. A feature of SRPPs is they can handle difficult loads and have high voltage output swings.

Good listening
Bruce

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PostPosted: 12 May 2010, 17:06 
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Location: Chilliwack, BC
gofar99 wrote:
A feature of SRPPs is they can handle difficult loads and have high voltage output swings.


I think that's mu-follower. SRPP can't handle fluctuating loads (they are optimum into one load-Z, then THD goes wild above and below).

Good reading: http://www.tubecad.com/articles_2002/SR ... nstructed/


Cheers!

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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PostPosted: 13 May 2010, 04:37 
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Joined: 08 Aug 2009, 03:11
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Can't edit this late in the game, so I'll toss in SRPP part-III :)

http://tubecad.com/2009/10/blog0173.htm

Cheers!

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* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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