I feel it is time to upgrade my 1977 system.......

Hello @glm911 and welcome to these shores.

You have a pair of excellent speakers and your amplification, while dated, is a very good vintage!

1) In your shoes, I would begin with an external phono for your TT. 1b) I would then check the usefulness of a superior cartridge.

2) Following that I would check the room acoustics and improve them as much as you can: there’s no point in improving a system you cannot hear!

3) Third, I would look into getting a ultra-high precision preamplifier. (Your power amp is quite good, even by contemporary standards (IMO). You could consider refurbishing it).

Of course 1 & 3 can be had in the same device. Purchased new these tend to be expensive. Used prices are much more attractive: a CAT Ultimate (tube) w/ phono is excellent and can be had for around 5k used. There are others, including ZOTL Ultralinear.

The above are tube based.

Regarding SS, Pass (mentioned above) is an excellent designer and his equipment is (intentionally) warm sounding. There are others, more revealing, and that match well with your kind of speaker: DartZeel, Symphonic Line...

There are of course, many choices and everyone here will offer at least one! If at all possible, it is worth trying out equipment in your system before you invest. You might find that your system is OK after all!

You’ve answered none of my questions.  Good bye and good luck. 

Less than six hours after posting the questions? Patience, grasshopper!

There is no doubt things have changed since 1977, and that budget allows for lots of possibilities. But I'd like to introduce another factor that has to be considered. If any of us listened to the same system for 46 years, might we not find any change could sound 'wrong' to our ears? Wear some comfy shoes for 46 years and then buy a new, expensive, bespoke pair of hand made Bluchers from Jermyn Street. Despite their quality and expense, they aren't going to feel 'right' at the start, are they? There is a danger of the same kind of thing here, so I'd go slowly and incrementally. Start small, with say, a new stylus on the cartridge. Maybe a new cartridge. Work up from that, just dipping your toe into the water of change gradually.

mesch

8ohm

You are like Buck Rogers in the 21th century!

Keep it simple. How about the new NAD C 3050 integrated? Retro NAD look….modern performance.

Or Cambridge Evo 75 or 150. I’ve been at it since that time also and been through a lot and have landed there at present. Consider these a modern Swiss Army knife of good sound.

Google search “Future Fi” That’s the place to be these days to take advantage of all the modern features available these days and it’s nothing like the 1970s, except phonos are still a thing.

Or KEF ls60 + phono and done.  

BTW I worked at a Tech HiFi store back then as a kid. Good times!

I don't think you need to spend anywhere near 18K to make a significant improvement to your system. A quality tube integrated amp would take you where the Altecs are designed to run. I'd look at a Prima Luna EVO 400. You'll have plenty of power with 70 wpc of tube power. Then spend a modest amount on interconnects and loudspeaker cables. I recommend solid copper wires. I'd also take dogberry's advice, that is spot on.