EFP 3 Q

[John Roman]

I've converted my extended foreplay to use 6SN7 output tubes. I've also recently been trying to complete the install of some Goldpoint attenuators. I have a question though. The socket for the original output tube (12AU7) was wired to pin 1, the plate/anode. But pin 1 for the 6SN7 is for the grid and pin 2 is the plate/anode. Does this change the way the Goldpoint's are wired?
input appreciated,
John

[Paul Joppa]

What?

All the pins are different between the tubes. You have to wire the triodes as in the circuit diagram, which means you have to choose which triode is the voltage amplifier and which is the cathode follower. Once you have done that, you will know which grid takes its input from the level control.

That may or may not answer your question; if it doesn't then we need more information.

[Grainger49]

John,

Do the tube swap. Look at the extended schematic (I assume there is an extended schematic, I don't know) and on the first triode (VA) you feed the output of the C⁴S to the plate of the first triode.  The cathode of that triode has an HLMP 6000 to ground.  The grid of the first triode is fed from the top, usually the input of the GPA. 

For the second half of the 6SN7 the second triode (CF) the plate voltage comes from the VR board for that channel, the grid is attached to the plate of the VA triode and the cathode is going to be attached to the C⁴S board.

In other words, first sort out the pin assignments.  Once that is sketched the first half will be like the first half of the 12AU7 in the schematic, the second half like the second half of the 12AU7 in the schematic.

BUT the tube pin numbers are all screwed up.  You just have to look at the two and make a list of what on the 12AU7 becomes which pin on the 6SN7.

[John Roman]

Thanks G