[sdiy] tube question 2: characteristics , DC versus 20kHz

[Antti Huovilainen]

On Thu, 28 Aug 2003, Grant Richter wrote:

> Has anyone seen a configuration where a zener diode is used in the cathode
> circuit of an inverting triode stage? I saw an old app. note where a zener

I have only seen zener used in biasing a power tube, but I see no reason
why it wouldn't work in a triode stage too.

> It seems necessary if a tube circuit is to handle +/- 5-10 volt signals at
> the grids.

This won't work. If you bias the tube so that grid is 5 volts negative
towards cathode, you're essentially biasing it straight into the cutoff
region. To get +- 5V signals to work you could either use a divider
before the grid or use local negative feedback (possibly using
differential input stage too).

Disclaimer: I've only built a tube guitar amp and done some software
simulation of tube preamp, so don't take my input as the final word on the
subject.

Antti

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