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In Reply to: RE: 811A - A2 amplifier posted by sganti on September 13, 2014 at 14:25:45
Here is the amp circuit
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How's the damping factor with that design?
Seems fine with the Def's
The bass is tight and not bloated.
I'm no expert but I think CB's question was a technical one.
I don't see any voltage feedback that would lower the plate resistance of the 811a but I do see current feedback that will increase the plate resistance.
What is the in circuit plate resistance of the 811a and what is the primary impedance of the output transformer?
Thanks.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
There is a 16 ohm winding from the o/p for local cathode feedback, which I use, that lowers the Rp of 811A
I really don't know Rp of 811A in A2 mode, but I have seen 811A amps using anywhere from 3.5K to 7K, so I settled for a James 5K that came with the 16 Ohm feedback winding.
ganti
I stand corrected.
The KNFB does lower the plate resistance.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I think it is fascinating that you use the 6L5 as your driver. This tube is the missing link between the 6P5 and the 6J5 and yet nobody uses them. I am just as guilty as I have a nice collection of 6L5s but have never gotten around to using them; instead I have been seduced by the sexy 'new' high transconductance pentodes and triodes released in the 1950s and 1960s.
I spent years (OK, decades) listening to the 76 and 5687 families of tubes and in the last few years I have tried branching out and trying new types. Having played with the new Triode Load Line Simulator for several days now, I am reminded that the 5687 family (7119, 7044, E182CC) are very linear tubes with extraordinary low distortion, at least on paper. I may end up going full circle back to the same old families of tubes but trying the 6L5 this time as the voltage amp instead of the 76 or 6J5.
I felt with a preamp in the chain, and with 811A biased at +20V, 6L5 had the gain I needed where I can turn the volume to little over half and the sound is loud. My speakers are Zu Def IV's and are 100db efficient.
I do like the sound of the 6L5, and had built couple of linestages in the past with a stepdown o/p transformer.
I will be experimenting with a lundahl plate choke for the 6L5 at some point.
Right now, just letting the amp play and break in..
ganti
Here is the filament supply and mosfet supply circuit
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