more loot from the eTf

Another year, another eTf. Similar to last year, here is some schematics to sink your teeth into.

Christof Kraus, proprietor of silvercore, was freely sharing some very interesting schematics. Christof started with the same jc morrison schematic that I am basing my coppatone work upon. But he ran with it in another direction and the results are blowing my mind.

Christof has already written up his work in four blog posts:

1. der 812A EGN
2. mehr Spass mit der 812A
3. der 805 EGN
4. einfacher Treiber für positive grid Röhren

Yes, that is in german, a quick test shows that google translate does a fair job. But I am happy to demonstrate what I like about them.

This is the complete signal part of a working amp. Add power and filament supplies and you are cruising. Love the ‘just tubes and iron’ aspect.

Hooking up the choke under the input tube like that creates a half-way house between full-µ choke-loaded gain stage as jc intended and a more traditional choke-loaded kathode follower: it gives half the tube’s µ as amplification and half its rp as output impedance.

Another cool aspect is that the output tube is positively biased. We have seen that before on this blog.

Can Christof go a little further? Sure he can:

The input transformer—ratio and hookup—is a bit more straightforward here.

Christof breadboarded some of the amps shown in the four posts at the eTf. Holger Barske made a nice photo of one incarnation:

You can see the chokes in front, 6-chamber jobbies for low capacitance, Christof says. Bandwidth is not an issue.

Go check out the posts, awesome food for thought.