[ARC5] Circuit Help Needed

[Kenneth G. Gordon]

On 10 Feb 2017 at 22:47, Tom Lee wrote:

> Hi Ken,
> 
> The 6SL7 here is actually connected as a common-grid stage (the right 
> half) driving a common-cathode stage in cascade. A cascode would have 
> the plate of one section driving the cathode of the other (the "-ode" 
> part of cascode).

Ah. Yes. of course! You're correct. My old eyes are deceiving me. -) Grid of one to cathode 
of second is cascode. Mark's is grid of one to plate of other.

> 
> The right-half of the 6SL7 is the error comparator -- it compares the 
> reference voltage (applied to the grid) to a sample of the output 
> voltage (applied to the cathode). That error is gained up without an 
> inversion in going from cathode to plate and drives the grid of the 
> other half of the 6SL7. That increases the gain even further, and also 
> inverts in going to the plate, which drives the control grids of the 
> paralleled 6V6s. There is no inversion in going from the grid to the 
> cathode of the 6V6s, so with only one inversion around the loop, we have 
> negative feedback, as needed.

Kewel! Thank you, Tom. It's simple when you know how. :-)

OK, Mark?

Ken W7EKB

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