Hi,
I'm curious about your thoughts about the difference between the two units.
What I see:
4274A:
- the older one
- it has one more digit (max 5.5)
- it has much wider external polarization voltage range by default (+/-200V) (yes, I know that a sepcial adapter can be used with the other one, but the 4274A can handles higher voltage without any support other than an external power supply or option card)
- the built-in bias supply cannot be adjusted from the front panel, a special remote controller is needed
- it can be used up to 100 kHz
- wider driver oscillator range (up to 5V)
- adjustable oscillator voltage
- oscillator monitor (either voltage & current)
- much heavier (~18 kg)
4276A:
- newer design
- seems to be a bit budget-oriented (LED range indication instead of dotmatrix display), a lot of Sony hybrids
- there are a lot of frequencies up to 20 kHz
- it only goes up to 20 kHz
- no oscillator monitoring
- one digit minus (max 4.5)
- it seems to be faster
- better built-in bias voltage design to +/-40V (it can be set on the front panel) (but it's optional)
- cannot handles higher voltage only with a special adapter
- there are only two test voltage settings (LOW and HIGH)
- although it has much more measuring frequencies, but the compensation is made only at some spot frequencies, and a second order interpolation is made from that measurement to the other frequencies
As far as a I know, they have a different front-end.
As I see although they're in the same accuracy range (0.1% basic error), but the 4274A looks to be more precise according to the datasheets. The 4276A can do measurements with 0.1% error only in a thinner range (e.g. caps 1nF-1uF/1kHz), the 4274A specced much nicer (the basic accuracy is valid in almost all the ranges).
The other curious thing is that although they work in the same impedance range (100 mOhm to 1 MOhm), but the 4274A can measures much wider range of the components at a given frequency (e.g. 100pF - 100mF vs 100pF-1mF at 1kHz).
So, all in all, the 4274A seems to be the "better" unit for me except the measuring frequencies selection up to 20kHz. I would choose the 4276A over the 4274A only in the case of doing impedance curves (up to 20kHz).