Usefulness of 6X8 tube?

korneluk · 14th December 2006, 03:56 PM

I have a batch of these tubes (from an organ) and I'm trying to figure out what to do with them. The problem is that the cathode is shared between the triode and pentode sections.

http://tdsl.duncanamps.com/show.php?des=6X8

Any ideas for a useful application?

-- josé k.

bembel · 14th December 2006, 06:13 PM

Hi Korneluk,
I don't have a link right now, but there are typical circuit to work around the the "common cathodes tubes" (each section having its own bias then), just dig around ...

Hope this helps.

Wavebourn · 14th December 2006, 06:36 PM

I would experiment, using couple of green LEDs in cathode well bypased by capacitor to minimize impact of a positive feedback, to find out what plate currents (resistors) are optimal for such couple. It is the easiest way.

Joel · 14th December 2006, 08:05 PM

Fred Nachbar has a project on his site using the 6X8 as a phase inverter, if I remember correctly.

Joel

PeteMcK · 14th December 2006, 08:21 PM

Fred's circuit is on this page...

http://www.dogstar.dantimax.dk/tubestuf/paraph.htm

DigitalJunkie · 15th December 2006, 01:29 AM

I miss Fred.

pelikanu · 21st December 2009, 08:33 PM

Look here for a nice ideea:

Tony · 02:44 AM

here is thread started by ray_moth: Radford pentode-triode LTP splitter

Miles Prower · 22nd December 2009, 05:52 AM

6X8s are quite useful as voltage regulator error amps.

Arnulf · 22nd December 2009, 09:15 AM

Quote:

Originally Posted by pelikanu

Look here for a nice ideea:

Apologies for being OT, but this picture is very interesting ! I have been contemplating something like this with my extra TV tubes (2x PCF80 + 2x PCL805 for single channel class-D PP stage).

My plan was 2x triode (current source & switch feeding/draining a capacitor) as triangle wave generator, driven in a loop by 2x triode (schmitt trigger operating the switch), PWM and input fed into 2x pentode (LTP comparator), driving power pentode pair (PP output) to full extremes. It would take approximately 20Vpp swing on the grids of output tubes to drive them into cut-off which should be doable.

This was supposed to be bass/sub channel but I have only modelled its JFET version in LTspice, I have yet to find enough time and determination to go for tube version (my assumption was many different supply voltages would be needed, which is a big deterrent).

The picture you posted looks simpler but I'm not quite sure about the oscillator's distortion (nonlinearity)

14th December 2006, 03:56 PM	#1
korneluk diyAudio Member Join Date: Jan 2005 Location: South Florida	Usefulness of 6X8 tube? I have a batch of these tubes (from an organ) and I'm trying to figure out what to do with them. The problem is that the cathode is shared between the triode and pentode sections. http://tdsl.duncanamps.com/show.php?des=6X8 Any ideas for a useful application? -- josé k.

14th December 2006, 06:13 PM	#2
bembel diyAudio Member Join Date: Aug 2006	Hi Korneluk, I don't have a link right now, but there are typical circuit to work around the the "common cathodes tubes" (each section having its own bias then), just dig around ... Hope this helps. __________________ Plus je pédale moins vite, moins j'avance plus vite !

14th December 2006, 06:36 PM	#3
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	I would experiment, using couple of green LEDs in cathode well bypased by capacitor to minimize impact of a positive feedback, to find out what plate currents (resistors) are optimal for such couple. It is the easiest way. __________________ The devil is not so terrible as his mathematical model! Wavebourn: We Create Creativity!

22nd December 2009, 02:39 AM	#8
Tony diyAudio Member Join Date: May 2003 Location: Palatiw, Pasig City	here is thread started by ray_moth: Radford pentode-triode LTP splitter __________________ http://www.electronicslab.ph/forum/i...?topic=32688.0 Last edited by Tony; 22nd December 2009 at 02:44 AM.

22nd December 2009, 05:52 AM	#9
Miles Prower diyAudio Member Join Date: May 2005 Location: USA Blog Entries: 2	6X8s are quite useful as voltage regulator error amps. __________________ There are no foxes in atheistholes www.dolphin-hsl.com

14th December 2006, 08:05 PM	#4
Joel diyAudio Member Join Date: Oct 2002 Location: Brooklyn, NY	Fred Nachbar has a project on his site using the 6X8 as a phase inverter, if I remember correctly. Joel

14th December 2006, 08:21 PM	#5
PeteMcK diyAudio Member Join Date: Feb 2002 Location: Sydney	Fred's circuit is on this page... http://www.dogstar.dantimax.dk/tubestuf/paraph.htm

15th December 2006, 01:29 AM	#6
DigitalJunkie diyAudio Member Join Date: Apr 2003 Location: Portland,Oregon Blog Entries: 4	I miss Fred.

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