I have to apologize to AFB for asking what the advantage is of the the 12A7 tubes over the 6AV6 tubes which are supposed to be one half of a 12A7 tube.
Now to the nitty gritty: If I understand correctly I could connect a 6 Volt tube such as the 6BQ7 without any changes to the wiring except connecting pins 8 and 9 on the tube itself to eliminate ground hum. Is this correct?
Next question: Post #3645 by Gibosi and AFB is a wiring instruction table for using 12A7 tubes. (Many thanks!) Looking at Gibosi's amp on post #3625 it seems to me that right and left is the opposite of post #3545. In post #3545 the left channel has five connections to the the adapter, and the right adapter has three connections.
It seems to me that the picture on Post #3525 has the opposite; the left channel has three connections, and the right channel 5 connections.
I think the 12Ax7 types are just made "better" (i.e., better construction, alloys used, design...) than their single triode "equivalents" -which are only that on paper really- designed for different applications like a three-in-one tube for car radios (detector, auto-volume control (or something...?) and amplification). The 12AX7 is basically just a high gain double triode, designed to do just that (voltage gain), and do it at least decently.
Yeah, different people have been wiring their adapters one way or another. My 12Ax7 adapter has the -three- heater pins wired to the left socket, while my -to be soon put to use- 6DJ8 adapter has the -two- heater pins and the shield wired to the right channel like all the cool kids (just because no one has managed to get rid of that ground through the left socket yet, and I'd rather be on the winning team lol).
For your 12AX7, both tube pins 4 and 5 are connected to socket 3. To use your 6BQ7, the lead for tube pin 5 must be disconnected from socket 3 and connected to socket 4. And tube pin 9 must be disconnected from socket 4 and connected to tube pin 8.
These connections do not have to be soldered as long as you have a very tight mechanical connection.
I agree that a tight mechanical connection is more than enough (wire leads squeezed tightly between the adapter shell and metal taps. I've had solder points burst or wires break (my wiring was way too tight on my 12Ax7 adapter) on my DIY adapters, but even when I manhandled the device back into submission and resoldered wires without taking anything apart, the wires on the Vector adapter side didn't even budge. Basically, the connection is more solid on the adapter side than on the socket side in my case... My second adapter is better though.