How's that, you ask?
Simple. I made up an adapter to go from an octal plug (based for a 7591) to a Novar socket (based for a 7868).
Since, for all intents and purposes, the 7868 and 7591 use the same load and voltage settings on tube testers (except for very slight differences in plate wattage ratings, they're essentially the same tube inside, except for basing), all that has to be done, is to transpose the base wiring from the 7591 socket layout, to the 7868 socket layout.
Here's the wiring that has to be done- there's only six wires that have to be run (two heaters, plate, screen, grid and cathode/suppressor). I made the wires short enough so that I could fold them down into the octal plug (mine was a replacement octal tube base, with standard tall shoulders- those can be ordered from various places, as can Novar sockets):
7591................7868
Octal plug ........Novar socket
1 NA
2 Heater...........4 Heater
3 Plate.............9 Plate
4 G2.................1 G2
5 K/G3..............3 K/G3
6 G1.................2 G1
7 Heater...........5 Heater
8 NA
I set the Hickok to the settings for the 7591, plugged a 7868 into the adapter, and plugged the adapter into the octal socket. Presto, works great!
This is a good work-around for those numerous tube testers without Novar sockets. Of course, this will ONLY work for the 7868- and only IF your tester has a setting for the 7591... NOT other Novar tubes with other basing!!
Regards,
Gordon.
Simple. I made up an adapter to go from an octal plug (based for a 7591) to a Novar socket (based for a 7868).
Since, for all intents and purposes, the 7868 and 7591 use the same load and voltage settings on tube testers (except for very slight differences in plate wattage ratings, they're essentially the same tube inside, except for basing), all that has to be done, is to transpose the base wiring from the 7591 socket layout, to the 7868 socket layout.
Here's the wiring that has to be done- there's only six wires that have to be run (two heaters, plate, screen, grid and cathode/suppressor). I made the wires short enough so that I could fold them down into the octal plug (mine was a replacement octal tube base, with standard tall shoulders- those can be ordered from various places, as can Novar sockets):
7591................7868
Octal plug ........Novar socket
1 NA
2 Heater...........4 Heater
3 Plate.............9 Plate
4 G2.................1 G2
5 K/G3..............3 K/G3
6 G1.................2 G1
7 Heater...........5 Heater
8 NA
I set the Hickok to the settings for the 7591, plugged a 7868 into the adapter, and plugged the adapter into the octal socket. Presto, works great!
This is a good work-around for those numerous tube testers without Novar sockets. Of course, this will ONLY work for the 7868- and only IF your tester has a setting for the 7591... NOT other Novar tubes with other basing!!
Regards,
Gordon.
