Emulating Old Tektronix Coded Probes

According to the manual of my Tek 465B scope, the coupling ring is connected through a resistor to the base of a transistor that controls the illumination of the 1X and 10X LED indicators. A typical probe (P6105) has an 11k resistor connected between the coupling pin on the probe body and ground. Thus when the probe is connected to the scope BNC connector, the transistor is connected to ground through this resistor. This changes its state which then turns off the 1X indicator and turns on the 10X indicator. If you could take the Tek probe BNC (with the coupling pin) and substitute it for the generic probe BNC, you might be able to make the probe sensing work.

If I recall correctly, the pin on the coupling ring shown in your picture of the Tek probe grounds the insulated ring around the connector on the scope to indicate that the probe is set to 10 X. If your probe is sufficiently intact, you could check this with an ohmmeter...

I don't think you could easily make a generic probe switch the indication to match the probe setting, but with a little ingenuity you may be able to make the generic probe force the scope to always indicate the 10X scale. If you don't mind making a small mod to the scope, you could add switches to the scope to change the scale indication, by grounding (or not) the sensing ring.

I experienced the following on my 2425A scope for the probe coding, with Rp being the resistance between the coupling ring and ground:

Rp               scaling
------------------------
>10k5            x1
8k5 < Rp < 10k5  x10
5k5 < Rp < 8k5   x100
0k5 < Rp < 5k5   x1000

Confirmed on a 2445