ECF801 Triode/Pentode any useful application ?
 

There are some Triode/Pentode combinations like ECF801 / 6GJ7 in which the two tube systems share a common cathode.
Are there any known applications where both systems can be used in a circuit ?
audio, power supply or whatever ?
I mean aside from their original purpose as oscillator/mixer in a frequency changer or using just the triode or the pentode separately ...

how about a Radford phase spliiter?....http://www.diyaudio.com/forums/tubes...-splitter.html

Paraphase/See-Saw is a good possibility. Since one system has 100% feedback, its parameters don't matter.

Yes, that may fit. Found this, think it's the same: New Phase Splitter
In this article the emphasis is more on phase stability.
I gave it a try but although I used ECF82 spice models I could not get symmetric output signals ... played varying plate resistors but could not get it right, yet.
Don't have model for ecf801 either.

so the 2nd (unity-gain) triode could be the pentode, right ?
The Valve Wizard

It's up to you ! If you want high gain, use the pentode for the amplifying first stage and the triode as second tube (slave). Otherwise, vice versa

The fact that you can't get the Redford symetric doesn't surprise me.
I don't like that circuit.
To use the ECL801 as a paraphase splitter try it like this.Didn't build it but looks promessing.
Mona

Yes, floating paraphase, I guess.
I like the split cathode resistor, makes it easy to match non-equal tubes.
Modifyed it a little, hooked up the pentode in triode mode. All I had to do is to change the upper cathode R to 220 and the lower R to 470 ohms. Et voilà - symmetric outputs.
Not that I need a phase splitter right now, but good to know ... maybe some day ...