Direct Coupling question

[angsuman]

Hello, I am new to direct coupling between stages. I would like to try it between my first and second stage in my amp. If I'm getting the idea right, I have to raise the voltage of my cathode until the difference between it and the plate is equal to the bias point of the grid, correct?

I was wondering if it is possible to do this with zener diodes and what are the potential benefits and drawbacks. I have linked to a schematic of what I am trying to do.


http://www.flickr.com/photos/1403176...37127/sizes/l/

Thank you.

[SY]

That will work, but injects all the noise and nonlinearity of the stacked Zeners right into the input of the second stage. You could also use a bypassed resistor in that spot, but that's just a back-door way to capacitor couple.

There are probably better topologies to use to get that second stage happy with the DC, but you may need to add another tube section or two. A cathode-coupled second stage might be an interesting alternative. When all is said and done, you'll have to figure out how to remove the DC from the output...

You might want to see if there's a copy of Landee's "Electronic Designer's Handbook" on line somewhere; there's excellent coverage of DC amplifiers.

[ray_moth]

You don't need to bother with zeners; a resistor will do the same job if it's sized correctly. Its value should be = (cathode voltage)/(tube current).