If possible purchase a classic tek O'scope like a 547 or even a 465, get a tek service manual then proceed to cal or repair it. These classic tek scopes are excellent teaching tools. There is MUCH that can be learned by working of these classic tek instruments.
The circuit design, mechanical design and overall consideration for serviceability and longevity was second to none. Back then tek built stuff to last, to be easily repaired and to stay in cal, in service for a very, very long time. Much of this is no longer true today for a host of reasons.
I'm sorry but that sounds like a lot of tosh. A 547, really? Don't get me wrong, this was a great scope in 1968, and it's still a nice collectible for someone interested in vintage T&M gear, but no sane person can reasonably suggest that this is a great every-day scope or techning tool half a century later. You must be kidding, right?
For example, your claim that "
the circuit design, mechanical design and overall consideration for serviceability and longevity was second to none" which is bogus. The epoxy HV transformers in these scopes was a pretty poor design which attracted moisture, which over time killed (if I remember right, it's been a very long time since I had one) the oscillator driver valve. The valves in these scopes also didn't appreciate short operating cycles, it took forever to stabilize, and the overall MTBF was pretty low, which is one of the main reason why Tek went from valves to transistors. The 465 runs circles around the 500 Series in terms of reliability, which is still worse than what can be expected even from older DSOs.
Your claim that these scopes were designed "
to stay in cal, in service for a very, very long time" is tosh as well. Despite the low bandwidth of these scopes they actually needed regular re-adjustment because of the aging (which was accelerated by the heat pumped out by all the valves) of many components. The 500 Series was pretty bad, later scopes built on transistors and ICs where much more long-term stable as they didn't produce a similar amount of heat and thermal stress. The 465 is much better than the 500 Series, but still has many analog components that age and shift the calibration over time, which is much less of a problem for any newer DSO because they automatically compensate for the shift of the few analog components they have.
And as a teching tool, serious? Unless you want to train museum curators the idea of using a 547 or 465 for teching EEs is bonkers. These scopes tech them very little that is relevance to a job as EE in 2015, these boat anchors are useless dealing with any of the complex signals modern technology works with. Using them as teaching tools would be a huge dis-service to your students because the time wasted on teaching how life was in the 60's could have been used for actually useful stuff like how digital scopes work, what their limits are and how to employ them for signal analysis. It may be nice for a short demo on how life was back then but that's about it.
The price one pays for smaller, lighter, portable and all that (modern DSO) comes with a cost and it is not initially apparent.
What price? Not buring 1kW for a primitive 50MHz scope which takes 20mins to stabilize to become usable? Not having mechanical switches which corrode and fail over time? Not having to re-adjust tons of analog trimmers and potentiometers to compensate for the shift due to aging (something modern DSOs compensate for automatically through self-adjustment)? Not needing to hunt for obsolete components which are out of production for decades? Not having to guess what the signal parameters are because the modern scopes can actually analyze it?
I'm honeslty curious, what is this non-apparent price one pays for modern scopes you're talking about?
I'm still using a tek 7104 at work, there is nothing modern that can replace it for the work I'm doing.
No offense, but unless your work is fixing vintage scopes or doing some simple analog audio work this says much more about you being stuck in the past than about the qualities of the 7000 Series.