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Usefulness of 6X8 tube?
Usefulness of 6X8 tube?
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Old 14th December 2006, 03:56 PM   #1
korneluk is offline korneluk  United States
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Default 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.


Any ideas for a useful application?

-- josé k.
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Old 14th December 2006, 06:13 PM   #2
bembel is offline bembel  Europe
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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 !
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Old 14th December 2006, 06:36 PM   #3
Wavebourn is offline Wavebourn  United States
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Usefulness of 6X8 tube?
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.

Nothing in the universe is perfect. The ideal things are the ones that are most optimal. Optimization criteria, what matters. When I hear "No Compromise Design", I want to take a sledgehammer and test how impact-proof it is.
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Old 14th December 2006, 08:05 PM   #4
Joel is offline Joel  United States
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Fred Nachbar has a project on his site using the 6X8 as a phase inverter, if I remember correctly.

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Old 14th December 2006, 08:21 PM   #5
PeteMcK is offline PeteMcK
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Fred's circuit is on this page...

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Old 15th December 2006, 01:29 AM   #6
DigitalJunkie is offline DigitalJunkie  United States
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I miss Fred.
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Old 21st December 2009, 08:33 PM   #7
pelikanu is offline pelikanu  Romania
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Look here for a nice ideea:
Attached Images
File Type: gif Compound_Tube_PWM(2).gif (9.6 KB, 704 views)
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Old 22nd December 2009, 02:39 AM   #8
TonyTecson is offline TonyTecson  Philippines
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Usefulness of 6X8 tube?
here is thread started by ray_moth: Radford pentode-triode LTP splitter
planet10 needs your help: Let's help Ruth and Dave...http://www.diyaudio.com/forums/plane...ml#post5010547[B

Last edited by TonyTecson; 22nd December 2009 at 02:44 AM.
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Old 22nd December 2009, 05:52 AM   #9
Miles Prower is offline Miles Prower  United States
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6X8s are quite useful as voltage regulator error amps.
There are no foxes in atheistholes
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Old 22nd December 2009, 09:15 AM   #10
Arnulf is offline Arnulf  Europe
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Originally Posted by pelikanu View Post
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)
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