High gain EL34 SE

[tubenit]

Posted by TristanC.   I thought this looked like a very cool SE project.

With respect, Tubenit

[BetterOffShred]

I came across this elsewhere the other day, and was going to start a thread about it asking if anyone has built this or tested it before, but then didn't.  Anyway, has anyone built this or tested it before?  It looks pretty awesome for sure.   I love high gain stuff of course, maybe I'll work on a layout in my free time over spring break! 
-Brett

[purpletele]

I like the labeling work on the schematic!

I can see an actual Cathode Follower circuit isolated.

[BetterOffShred]

So I've been studying this schematic a little more and working through Chapter 1 of Merlin's book, and I'm confused by C2.   He implements something similar in a few things in chapter 1, and it's referred to as "Cs" a power supply smoothing capacitor.  In the designs in the chapter, it is wired up before Ra (R3 in this schematic) the anode load resistor, and directly to ground, rather than to ground via R4 (Cathode resistor) in this schematic.  I was wondering if anyone who's got the tech on this would care to comment on this design choice?  Is this to reduce noise in this gain stage? I want to learn!

Also, he only has a 10k for an input grid stopper resistor, I've typically seen 33K or higher (Fender 68K on the input jacks etc), he details a setup like this on his site using a 470p to ground right after the 10k grid stopper, but that is absent on this build.. I know the higher the value of resistor the more Johnson noise you create, but by using this smaller grid stopper, isn't he changing the effective input bandwidth?  He uses the equation: Rg = 1 / (2 pi f C) = 1 / (2 pi × 20000 × 200 × 10^-12) = 39789 ohms, showing the input capacitance of 200pf and 20khz cutoff..
It's just a curious design and I'm too much of a noob to know what exactly is happening.

-Brett