P6046
The Tektronix P6046 is a differential probe and amplifier. It was initially intended for use with a 1A5 and attaches through a special multi-pin connector. A separate amplifier was available as an option to use the probe on a 50 Ohm input scope set at 10 mV/Div.
With a 1A5, it has a 45 MHz bandwidth. The raw bandwidth of the probe and amplifier is 100 MHz. Note that the probe itself acts as either a 1X or 10X attenuation probe dependent on a signal voltage on pin D of the connector. When used with the amplifier, 10X mode is used in the 200, 100, and 50 mV/DIV settings and 1X mode for 20, 10, 5, 2, and 1 mV/DIV.
Operation
Ground the probe! Seriously. Sticker the probe "Ground Me!" The two probe tips are (in DC mode) directly connected to the gates of a pair of JFETs. Use the shorting plugs on the tips when not in use. I also recommend stickering the probe amplifier with the ATTEN BAL setup proceedure from section 2-6 of the manual.
Repair Issues
Pay attention to the maintenance section of the manual about the operation of the P6046 outside it's housing. The bottom section of housing ties the circuit grounds together. The schematic diagram calls out four different grounds: The cable (using the three line earth symbol), the front posts (triangle-1), the middle mounting screw (triangle-2) and the rear posts (triangle-3). When operating the probe without the top housing, reattach a front and rear post screw to hold the board down to the lower housing. When operating the probe with no housings, tie a front and a rear post together with a jumper. The center circuit board mounting screw ground is only used for the high frequency CMRR adjustments and none of those will work without both housings in place.
The input FETs must be a matched pair. A possible replacement is the 2N4416A. The matching criteria should be Idss.
Calibration
The Tektronix P-6046 is excellent, and usually quite inexpensive because nobody knows what it is. Make sure it works when you buy it, because these probes are extraordinarily tricky to trim up for CMRR after repair. -- Jim Williams. The Art of Analog Circuit Design.
Newer versions of the probe have plastic plugs that allow access to the following adjustments
- R209 - 42 MHz CM balance
- C209 - 18 MHz CM balance (and drain voltage measurement)
- C245 - 50 MHz CM balance
- R155 - Gain
The full calibration shield has access to all ten adjustments. You will need to make this by drilling holes in a housing. The full shield is needed to recalibrate a probe after replacing the input fets. Some used probes will be found with an access hole drilled for R235 (GAIN SWITCHING BALANCE) since this is adjusted to remove the trace shift when the probe switches from 1X to 10X mode.
