pcf86 triode pentode - possible one bottle preamp?

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ioaudio

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Joined
May 11, 2005
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digging into various tube data sheets i stumbled across this one:

PCF86.gif


more detailed data sheet

a triode and pentode in the same housing...sounds intriguing to me.
i would like (us) to design a high gain one bottle preamp with a "modern" 10k unbal output. one bottle/channel should make it easy to stuff four channels into a mobile housing for on location recording. you´d rarely need 600 Ohm for such tasks.

one problem which attracts my eyes is the fact that the cathodes are internally connected.
how would you wire it?

-max
 
hi, I have some 6ab8/ecl80 which presents the same issue of a shared cathode connection...the ecl80 is a triode and pentode and the data sheet says the pentode is good for audio output to 2.5 watts...
curious if there is a good application for this type of tube (triode/pentode cathode connected)

the only topology that comes to mind is cathode follower into grounded grid or some kind of LTP...???
 
The clue is in the title: frequency changer. These devices are desgned for modulating, so could at a pinch be used in a compressor or an effects unit, but not recommended for general linear amplification.

You would have an issue with powering the heater in the Pxxx valves. They were designed to run in a 0.3A current-controlled heater chain, and took whatever volts they needed at that current.

The shared cathode was quite common in dual valves to save pins. It was usually assumed that the designs would be common-cathode with the cathode resistor heavily by-passed.
 
yes, the ecl / pcl tubes were quite common in reel to reel recorders for the speaker amp, using the pentode section for the output/current stage.
presuming that the pentode stage of the ecf / pcf series have nicer low currency characteristics, i would run it in another way: running the pentode as input gain stage and the triode as second stage. something like this:
micpre_8.JPG


maybe a cathode follower would be better?
 
when i get my breadboard and variable ps built i will try running a tube like this in parallel. any experience doing this? I understand that a tube capable of more current swing like an output pentode, is good for driving a step-down tranny; like a line out...would it hurt to parallel the triode section
 

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