Dave wrote:

I have a freshly repaired and calibrated B&K 747 and have
begun finally testing and cataloging my vast tube collection.

My question: surely someone sometime has figured out how
to wire a 4-pin socket to 8-pin plug for testing all the old
triodes - 45, 26, 01, and all the rest.

Just wire it up. It doesn't matter what the pinout is, as long as you
set the switches so that the right pins on the octal socket are connected
to the right pins on the tube.

Anyone have any info on this, maybe with a wiring diagram
for the adapter and 747 settings for some of the more common
types? I'm certain ANY tester could be made to do this, given
it has the right voltages available.

Well, start with say a 6SN7. The filament voltage is 6V, the
transconductance should be around 3,000 on each side.

Pins 7 and 8 go do the heater, 6 to cathode 1, 5 to plate 1, 4 to
grid one. Make your adaptor up to go to the heater, plate, and grid.

NOW, start with the settings used for element 1 of the 6SN7, but
change the cathode switch so that the cathode connection is sharing
the pin with the grid connection. Set the filament voltage appropriately.
Keep the same bias voltage, which I think should be in the ballpark
for those tubes.

Then get some good tubes with known transconductance, put them on the
tester, and adjust the load until the meter reads properly.

Voila! Mark down the settings. You now have a way to test 4-pin tubes.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."