ECF801 Triode/Pentode any useful application ?

[Sorento]

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 ...

 

[TonyTecson]

how about a Radford phase spliiter?....http://www.diyaudio.com/forums/tubes-valves/140028-radford-pentode-triode-ltp-splitter.html

 

[the_manta]

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

 

[Sorento]

how about a Radford phase spliiter?....http://www.diyaudio.com/forums/tubes-valves/140028-radford-pentode-triode-ltp-splitter.html

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.

 

[Sorento]

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

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

 

[the_manta]

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

 

[Ketje]

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

 

[Sorento]

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 ...