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Juergen Knoop 21st August 2009 09:28 PM

PCF801 Suggestions
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I have a bunch of PCF801 (combined pentode/triode w. common cathode) lying around and would like to build my first tube preamp with them.
Thought about a buffer+grounded grid circuit with heavy negative feedback. :cool:
Should I use the triode connected pentode as buffer or the triode?
The frame grid triode may be less affected by low anode voltages, so it may better be used as the grounded grid part.
I want as much open loop gain and less open loop distortion as possible.
Any suggestions?

AND would it work at all? :confused:
simplified schematic attached....

kavermei 21st August 2009 09:47 PM

You could get some inspiration here:

Juergen Knoop 28th August 2009 09:19 PM

thank you, I already hate this tube...connected cathode...grrrr

kavermei 29th August 2009 06:55 AM

Looks like that guy in the link is thinking in the same direction as you are with the GG configuration.

Just try it... you would have something unique...!

Boeing 8th September 2009 02:50 PM

It is great if you build it with Mu stage schem. Easy to drive the next power tube.
Try it so you will happy on it.
Good luck.

aardvarkash10 8th September 2009 08:41 PM

anti-triode, anyone?
swinging around a CCS tail, triode input side, pentode as anti-triode in a p-p VERY low output amp or a headphone amp?

jerluwoo 9th September 2009 12:33 AM

1 Attachment(s)
Here's a good starting point for ya. I based it on the standard operating points from the datasheet so it should work out fairly close.

arensattic 2nd November 2015 03:40 PM

PCF801 line stage on Thai website: why does it not work?
1 Attachment(s)
Hallo folks,

Like the previous writers in this thread I would like to build something with the TV tubes which are present in large quantities in my junkbox. Searching for PCF801 applications in audio, I found the attached schematic on a Thai website. I have built a prototype but found out that it does not work! (there is no audio at the output). Yet, the voltages and currents for the triode and pentode sections of the tube are quite OK (they are as indicated in the schematic). Can any of you comment on this finding? I wonder whether there could be any mistake in the schematic. Should the 47 uF cap which has been drawn from anode to ground in real life be connected from the B+ rail to ground?

NB it is of course possible that I made a mistake in the input/output connections, I will still check this.

Thanks in advance for any wisdom you may have,

Aren van Waarde
(aka arensattic)

DF96 2nd November 2015 03:48 PM

The circuit looks OK to me. Probably a wiring error.

arensattic 2nd November 2015 08:01 PM

Circuit as drawn is OK
Hallo DF96,

You are right, there was indeed a broken wire in the output cable! After this was repaired I could perform some listening tests. Tested with a portable CD player as signal source and my old and trusty signal tracer as amplifier, the sound of the circuit appears quite OK (good reproduction of the human voice, no hum, no noise, no microphony). But I have not yet looked at the output on a scope (hopefully there are no RF oscillations). Anyhow, the circuit as drawn seems a good start for further experiments.

I have collected several RIAA phono preamp, line level preamp and power amp circuit ideas using P-type tubes, thus after further experiments I may continue this thread. It will perhaps finally result in a completely (Tele)visionary audio system! :):):)

Best regards,


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