TDS 754A vs TDS 754D

[Tony_G]

Hi All,

I'm looking to grab one of these 500MHz scopes and do the 1 GHz upgrade - I've never used the 754A or 754D series but the 754D seems to command higher prices.

The use case is to measure rise times in old HP test gear (at least initially) - Should I go with the 754D for additional money or save some bucks on the 754A?

Basically is what Tek added to the 754D really worth it?

Thanks,

TonyG

[David Hess]

I am not even sure what the differences are between the 754A and 754D; my notes do not show anything.  Both have phase and magnitude FFTs, DPO capability, and segmented memory.

If you are only interested in transition time measurements, then a sampling oscilloscope like a TDS820 or TDS840 might be better because of its much higher bandwidth assuming that you have a pretrigger signal available.

[Tony_G]

Thanks - I'll take a look at those - While I'm looking at Rise/Fall times now I also don't want to be stuck with a scope that isn't more generally useful - I've heard that the 600 series can give great results on bandwidth but just isn't a very useful general purpose scope - Having not used Tek gear in many many years I really don't have any experience to claim one way or the other.

TonyG

[nctnico]

If you intend to hack the scope I'd check whether the TDS754D can be hacked to get the 1GHz bandwidth. Also be aware that you have to go through the calibration procedure which requires various HF signals and equipment.

[Tony_G]

Thanks nctnico - I'm working off the message here:

https://www.eevblog.com/forum/testgear/conversion-of-500mhz-tds744a-to-1ghz-tds784a/msg569022/#msg569022

i can confirm the modification. I have a TDS754D, which i upgraded to TDS784D by changing the ID resistors. However, the calibration failed, because freqency response was out of spec (1 GHz was low by ~-4 to -5dB). After removing the capacitors, the calibration runs now flawlessly, and the Field Adjustment software
says it passed calibration

To do the recalibration I can get into our lab here at work with proper equipment. I'm intending this for my home/personal use so I'd rather not be bringing a bunch of stuff in to use work gear but instead use this at home.

TonyG

[David Hess]

Thanks - I'll take a look at those - While I'm looking at Rise/Fall times now I also don't want to be stuck with a scope that isn't more generally useful - I've heard that the 600 series can give great results on bandwidth but just isn't a very useful general purpose scope - Having not used Tek gear in many many years I really don't have any experience to claim one way or the other.

TonyG

That will be the case; sampling oscilloscopes have no substitute for bandwidth (and overload recovery) at a given cost but are not general purpose instruments.  On the other hand, calibration of a 1 GHz hacked TDS754A or TDS754D may be outside the range of test equipment that most people have available.

[snoopy]

Hi All,

I'm looking to grab one of these 500MHz scopes and do the 1 GHz upgrade - I've never used the 754A or 754D series but the 754D seems to command higher prices.

The use case is to measure rise times in old HP test gear (at least initially) - Should I go with the 754D for additional money or save some bucks on the 754A?

Basically is what Tek added to the 754D really worth it?

Thanks,

TonyG

The 754D scope has digital phosphor and usually go for more than the 754A. Bear in mind that you will probably have to service the attenuation modules if the signal path compensation fails. I am in the process of doing this to a 784A where some of the relays have gone completely open circuit.

cheers

[Tony_G]

Thanks all - I ended up making an offer that was accepted for the scope so fingers crossed on the experience.

TonyG