Mu Stage

All the parts have to be put together at some point. Have fun!
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dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
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Mu Stage

Post by dave slagle »

hey all.

I have been staring at this image for some time now and I just don't get it. I'm referring to the mu-stage and I get how the pentode is an active load but the load on the 6SN7 is the 6.8K resistor in series with the parallel combo of the pentode cathode impedance (high) and the series string of the 390R + 33K resistor to ground. So isn't the load on the SN7 essentially 40K?

Can this be simmed with a tetrode model / what role does the suppressor grid hold?

dave

From DHT Robs site.

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reVintage
Posts: 365
Joined: Fri Sep 07, 2007 9:54 am
Location: Sweden

Post by reVintage »

Na,
This isn´t a typical mu-follower, actually it is the Kimmel mu-stage. Bootstrapping makes the 6,8kohm be like some Megs high. In other words the 33k+390 isn´t seen by the triode.

I would rather use a voltage controlling gyrator to get better control of the Ua of the triode though.

Check Kimmels paper http://www7.taosnet.com/f10/mustage.html where you can see this application called hybrid mu-stage with a MOSFET on top. It can though be used with a high Gm pentode on top and a high Gm triode below to simplify and better things a lot. I doubt the 33k is necessary. But maybe this another circuit. This one has been discussed by me, Michael Koster and a few others in another forum.

Can do a sim to show with D3a and a triode strapped 6E5P. I doubt the cathode follower function is necessary though when driving a 300B. Probably an anodechoke or 1:1 bifilar would be better.
Brgds
Lars
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

Hey,

Thanks

I know it is the kimmel approach. I had a hunch that something tricky was going on just like in the cathodyne phase splitter.

i'll do up a sim at some point

dave
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