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In Reply to: RE: need some advice ... posted by vinnie2 on July 31, 2017 at 16:00:48
Got things sorted out a bit. For the schem shown, the pins shown in the tube manual as 6,7 & 8 are for the left hand side of the tube and pins 1,2 & 3 are for the right hand side of the tube as shown. I know this because if you hook them up the other way 'round the gain is very mucdh reduced. So I guess if you hook it up the other way you are trying to run it backwards?
Still need to get the voltages adjusted as the plate to cathode voltage is still 150 vdc. May be time to try blackplates suggestions and see what that does.Curious to see how it sounds with the proper voltages.
The 6dj8 has two triodes that totally independent except for a shared heater.
They are identical except for small differences in the inter-electrode capacitance's that will make no difference in your application.
The image above shows that one of the two triodes uses pins 6,7 and 8 with pin 6 being the plate and pin 7 being the control grid and pin 8 being the cathode.
The other triode uses pin 1 for the plate, pin 2 for the control grid and pin 3 for the cathode.
Other than layout, it will not matter which triode you use for which stage of the amplifier.
I hope that made sense to you. If not, please ask questions.
Have Fun and Enjoy the Music
"Still Working the Problem"
You are getting good advice from a lot of guys who are much more knowledgable than I, but your comment about a difference in gain makes me wonder whether you are attending to not just which pins subserve which "side" of the tube but also which pins are attached to the plate, grid, and cathode of each section, respectively. Any good tube manual should show you a diagram of the pin arrangement in which the function assigned to each pin is labeled. You could possibly get the very different results you hint at if, for example, the plate and cathode pins for one side have been wired up backwards (plate circuit to cathode pin, cathode circuit to plate pin). So, you might want to double check that. Any error in wiring will of course make a huge difference in the result.
Yes, there is a physical left and right side of any dual section tube depending on your viewing angle. But that has nothing to do with electrical performance in a twin section tube.
If the two sides are the same, such as a 12AX7, the the only differences would be minor manufacturing tolerances. And even at that the left or right side could be the favorable section depending on the application.
Now there are quite a few dual and triple element tubes with drastically different sections like the driver tube in a Dynaco ST35, a 7247, which IIRC is half a 12AX7 and half a 12AU7. In this case you do have to be careful how it's wired.
But it should not matter much at all which side of a twin tube is used provided you don't violate proper circuit layout as mentioned above. If the two sides are much different in a twin tube, I'd say you have a bad tube!
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