Recently I scored A6302 for fair price and then I bought the old AM503 amplifier.
In principle it works, but it is really vintage, crusty, drifty and likes to pickup all kinds of noise. People say that AM503A or AM503B are better, but these things are stupidly expensive for what they are (especially to what I paid for the probe).
I was thinking about building my own amplifier, a bit of DIY, I could learn something and it shouldn't be extremely expensive. I can always use the old AM503 if it doesn't work.
I've analyzed AM503A service manual and schematic and also watched tesla500 videos on TCPA300 repairs. In these amplifiers the signal path seems to be as follows (simplified):
Hall Sensor (probe) -> Hall PreAmp -> Power Amp for bucking current -> AC coil (probe) -> Attenuator (rotary switch or a bunch of relays) -> Output Amplifier (gain, switchable BW limit etc) -> 50 Ohm Output
TCPA300 seems to be made out of off the shelf parts, AM503A (according to the schematic) still has Tek favorite in-house hybrids : attenuator an output amp. Not sure about AM503B.
However, new probes don't have these separate amplifiers at all! TCP202A or Agilent N2893A that HighVoltage repaired recently (
https://www.eevblog.com/forum/testgear/agilentkeysight-n2893a-current-probe-(teardown-and-repair)/) seem to only have Hall PreAmp + bucking current Power Amp, no switchable attenuator or amplifier.
How does this work then? Are the designers relying on the scope's front end attenuation & amplification circuitry? What voltages can be expected out of the probe transformer (also fed with bucking current)? AFAIR the output from the probe transformer is 50 Ohm, but some scopes with built-in 50 Ohm input impedance have relatively low input voltage range (like 5V RMS) so it worries me a bit.
If I can too skip attenuator & output amplifier then it would greatly simplify my DIY efforts.