How to wire tubes

[joecool85]

How do I know what pins go to what wire?  I'm working from this schematic: http://www.sophtamps.ca/schematics/sopht_12al8-v2.jpg

It says about how to wire the heaters, but that's it.

[noobiePT]

hey, i found of the 12U7 ( http://tdsl.duncanamps.com/show.php?des=12U7 )
the other couldnt find, do you know if any other type of tube can be used?

[joecool85]

hey, i found of the 12U7 ( http://tdsl.duncanamps.com/show.php?des=12U7 )
the other couldnt find, do you know if any other type of tube can be used?

But using that and the schematic I still don't know what wire goes to what pin on the socket...

[teemuk]

http://www.radiomuseum.org/tubes/tube_12al8.html

[joecool85]

http://www.radiomuseum.org/tubes/tube_12al8.html

So what pin goes to R2 for instance?  How do I figure that out?

[numpsha]

Check the other thread you have going on this.

http://www.ssguitar.com/index.php?topic=550.msg3811#msg3811

Rob


Use the Force -- Open Source!

[teemuk]

See the diagram in the link posted by NoobiePT. It shows the socket pinout of the 12U7 and a diagram of which pin is which in the tube. 12U7 is a so-called dual triode so it has two triodes inside it. In the diagram, you can see them at left and right. Pins 4, 5 and 9 are for the heaters and the rest are as follows:

Triode 1 plate: 1
Triode 1 grid: 2
Triode 1 cathode: 3

Triode 2 plate: 6
Triode 2 grid: 7
Triode 2 cathode: 8

Since R2 goes to grid of one of the triodes you use either pin 2 or 7. If you choose pin 2 then you correspondingly use pin 7 for the grid in the next stage or vice versa. The schematic already tells how to wire the filaments.


12AL8 is dual tube as well but it has both triode and a tetrode so you are forced to follow that pattern (tetrode to output, triode to 3rd stage). Diagram in the link again shows the pinout.

[joecool85]

Alright, thats starting to make more sense.  Before I wire anything up I will photoshop in the numbers on the schematic and have you guys double check I have it right 

[joecool85]

This is what I needed:



Thanks to: http://www.allaboutcircuits.com/vol_3/chpt_13/3.html

[joecool85]

I think I got it.  Someone want to double check for me?

[noobiePT]

hey, nice site you putted there..didnt know it, thanks 

as to the tubes, looks likes its allright

[joecool85]

hey, nice site you putted there..didnt know it, thanks 

as to the tubes, looks likes its allright

Alright meaning perfect, or alright meaning it'll probably work?  I want to get it just right before I wire it all up.

[teemuk]

The final tetrode stage may have an error:

Although the sopht schematic shows it differently I believe that (typically) when tubes are depicted the grid order (from bottom to top) is following:

(control) grid (where signal goes), screen grid (tetrodes), suppressor grid (pentodes), and so on for other tubes.

See...
Tetrode:

Pentode:


If that is the case as well in the site showing the 12AL8 pinout (those pics are poor) then you should switch order of the pins 3 and 2. I'm not saying you have it wrong now - I'm just saying there is a possibility for that and you should check it out.

[teemuk]

Ok... It seems that I was wrong. The pinout is correct as is. See the last page in:

http://www.mif.pg.gda.pl/homepages/frank/sheets/137/1/12AL8.pdf

[joecool85]

Ok... It seems that I was wrong. The pinout is correct as is. See the last page in:

http://www.mif.pg.gda.pl/homepages/frank/sheets/137/1/12AL8.pdf

I had looked at that pdf myself, it helped quite a bit.  So the image I posted should be correct?  I just want to make sure before I build it.