The 120K record length limitation isn't all that "poor" when you consider that it's used for single-shot acquisition at 10 GS/s.
It is, because the tiny sample memory means that the period you can capture at full sample rate is ridiculously small (12us with the optional 120kpts "large" memory option if my math is correct). It also means that to capture longer periods the sample rate will have to drop noticeably so that the tiny memory covers the whole period, i.e. the sample rate already drops if you extend the timebase beyond 1us/div.
120k points would be considered poor for a scope with slower sample speed already, and that is even more true for a fast sampler like the TDS694C. The TDS600 Series is pretty badly balanced, which makes them a poor choice for pretty much anything except some niche tasks, and together with the other issues (i.e. the trigger IC overheating nctnico mentioned, which is simply poor design, or the failing LCD shutter) makes the TDS600 a pretty poor choice.
The 694C was already the priciest scope in the entire Tek catalog during the years when it was offered (2000-2003-ish), and it's not clear who would have been willing to pay for more acquisition memory.
Pretty much everyone who wanted to capture longer periods or make use of long memory for sequence mode. Remember that 120k would already be poor on say a 2GSa/s scope, and the higher sample rate of the TDS694C (which equals to a larger amount of data) only makes matters worse.
In addition, the TDS694C wasn't exactly cheap when it came out, it did cost the same (or even more) than comparable scopes from other manufacturers at that time which all came with more sample memory.
It's worth asking what other real-time DSOs will get you to 3 GHz in the sub-$2000 range.
Sub-$2000? Not sure about that, most of the TDS694C seem to go for closer to $2500 - $3500 which isn't exactly cheap. $2000 pretty much only buys you "untested" (yeah, right) or broken ones. That's a lot of money for such a an old and (aside from bandwidth and max sample rate) pretty basic scope.
I'm not familiar with LeCroy's offerings; do they have a 694C competitor that people in that market should be looking at?
Well, it depends on where the priorities are. In the age and somewhat similar price range of the TDS694C there are essentially three LeCroy scopes, the older WavePro 960, the successor WavePro 7300, the WaveMaster 8400, and the WaveRunner 6200.
The WavePro 960 is a 2GHz scope (50ohms/1M switchable inputs) which offers 16GSa/s and up to 64Mpts memory (standard is 1M), and which came out around the same time as the TDS694C (end 1999/early 2000). The 950 is the largest model (there's also the 1GHz 950 and the 500MHz 940) and like other LeCroy scopes it comes with a pretty long of available options which includes advanced triggers, advanced math and FFT, Jitter and Timing Analysis and lots more, however it doesn't do serial decode. But it does come with a nice large 10.4" TFT display (no CRT), it boots quickly, and the UI is pretty straightforward. The WP900 was the last of LeCroy's VxWorks based upper high end scope, it was manufactured by Iwatsu, and has shown to be rock-solid (the only weak spot is the plastics front cover which tends to crack in the lower right corner, however a replacement can be bought for $20 or so).
With some patience you can find working WavePro 960s for below $2k, but they can often go for between $2k and $3k (so roughly the same price range as the TDS694C).
If 3GHz is required then one would be looking at the successor WavePro 7300 (non-A model) which came out around late 2001/early 2002. It's more expensive than the TDS684C but it's also a completely different generation of scope i.e. 20GSa/s with up to 72M memory and touch screen which runs Windows 2000 (can and should be upgraded to XP) for which a huge range of options is available, including serial decode for a wide range of common and less common/niche/obscure protocols. As the older WavePro 950 these scopes are very reliable (especially under Windows XP) if using the latest software (these scopes are still supported with updates!) and not messing with Windows settings. Aside from the front cover (which is the same as for the WP900) the only real weak spot is the hard drive, however this is a standard IDE drive that can be replaced easily. Otherwise these scopes are solid like a rock. As with the WavePro 900, the WP7000 Series does have 50ohms/1M switchable inputs.
Like all LeCroy mid-range and high-end scopes since the 9300 Series both WavePro 900 and WavePro 7000 use the LeCroy ProBus interface for which the second hand market often has a good selection of reasonably priced active probes.
However, there's also the larger WaveMaster 8000 Series which is basically the higher bandwidth variant of the WavePro 7000. The WM8000 Series starts with the WM8400 with 4GHz bandwidth (WM8500: 5GHz; WM8600: 6Ghz) and comes with 50ohms inputs with ProLink interface. Aside the bandwidth and the front end the scope is pretty similar to the WP7000, with up to 20GSa/s sample rate (however, standard memory is 4M/8M, with up to 100M). Because the WM8k comes with a 50ohms only input it can often be had for less than a WavePro 7000. I've seen a WM8500 go for approx $3500.
Last but not least there's also the WaveRunner 6200, 1 2GHz scope with 10GSa/s and 2M standard (up to 24M). As the Wavepro 7000 and WaveMaster 8000 this is a Windows 2000 based scope which comes with a wide range of options including serial decode, although the list is somewhat shorter than for the WP7k/WM8k. The LCD screen is smaller (8.4"), too. As with the other scopes, the WR6000 is a very reliable scope without any known flaws (again aside from the hard drive, but hard drives are essentially consumables anyways). WR6200s are pretty rare but I've seen them go for roughly the same money as a WavePro 960.
None of these scopes suffer from overheating, capacitor plague or any other major flaw that can be found in the old TDS Series. In addition, unlike the old Tek scopes even the old WavePro 900 can be sent to LeCroy for repair, and spare parts are also still available. Tek doesn't even service many scopes that are much younger.
However, if price matters most and one can live with 2GHz bandwidth then I'd say even an Agilent 54720D with 54722A (2Ghz 8GSa/s plugin with 256k memory) is a better choice than a TDS694C, plus like the LeCroys above it also doesn't suffer from overheating ICs. And the 54720D/54722A combination should be even less expensive than the LeCroy scopes above or a TDS694C.
At the time I was shopping for mine, the next step up would have been an HP 54854A at more than twice the price.
Understandable since the is a much more modern scope than the TDS694C. The 54854A offers 4Ghz bandwidth, up to 20GSa/s sample rate, double the memory as standard (262k) than the TDS694C has when fitted with "long" memory, can have up to 32M sample memory, offers a range of advanced options including serial decode, comes with an LCD screen, and is overall a much better balanced scope than the TDS694C.
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