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

@curtdr wrote:

"If you're intent on keeping the Altecs, OK... but speakers too have come a long way for the money.  If you like lively and yet with that "audiophile classy sound" and old-school looks: Klipsch Forte IV.  aprox $5000"

My Model 19's superseded Harbeth 40.2 Anniversaries and Dynaudio Confidence C4's and I can say without reservation that I get more enjoyment from my 45 year old refurbished Altec's than the well regarded Harbeth's and Dynaudio's... so one should not assume that newer speakers are better or more enjoyable that classic vintage speakers.  If the OP is satisfied with his vintage speakers, I would not replace them with something newer without validating  first hand that newer is automatically better.

@pdreher I agree for the most part and myself I own and love Epi 100 speakers and their little brothers Epi 50, with some updated parts from Human Speakers.

So, as I don’t know the Altecs in question, I don’t necessarily assume that new speakers are "better" than those... though I’ll note that even you have refurbished Altecs.

However, that said, speakers, like amps, have come a long way in "bang for the buck" since the 70’s, especially when you factor inflation, and there are some relatively inexpensive, $2000-5000 range, choices that perform at an astounding level that only the very, very best from "back in the day" could aspire to. Think about the updates over time to the JBL 100, the KLH 5, and the Klipsch Heritage... There are also far more choices in even less expensive "budget" speakers these days that only a select few from the 70s could come close and that only if updated.

I have Altec Flamencos and recently asked for some advice on amplifiers that you might find helpful. Coincident Frankensteins and Music Reference were recommended for my speakers as well. Also Atmasphere thought that his class d monoblock amps worked well with his similar high efficiency speakers and should be a good pairing for the Altecs. 

 @alexberger gave me the following useful info regarding amplifiers and crossovers:

" I have experience with Altec 604E that has similar sensitivity to Altec 846A. In the mid size rooms that I had 200-300 sq feet, 300B SET has enough power. I used McIntosh MC30 monoblocks (30+ watt), Marantz 8B in triode mode (20 watt), and 300B SET (6-7 watt). I also heard 2a3 Boothed monoblocks with my speakers and they were good enough in terms of power. The 30 watt McIntosh MC30 sounded great with my Spendor 2/3 speakers but with super sensitive Altecs it sounded rough and not as natural and refined as a 300B amplifier. 
What is really important is that for a 300B amplifier it has to have a powerful driver tube like 6f6, 6v6 but not popular but weak 6sn7.
The strong power supply with a big and good quality capacitor.
If your room is not huge, I suggest you try Coincident Frankenstein 300b monoblocks or Aric Audio Super 300B SET. Both these amplifiers have powerful driver tubes, interstage transformers and good power supply.

There are a lot of information about crossovers for Altec on Jeff Day page. Jeff prefers Hiraga schematic crossover for his Altec speakers.

https://jeffsplace.positive-feedback.com/

https://jeffsplace.positive-feedback.com/%e2%99%ab-vott-system/

I have Altec Valencias (Heathkit 101’s). I bought them because I was curious about the Altec sound. Short story, I love ’em! I alternate them in with my Von Schweikert db99 speakers.

Interesting that the Franks have been brought up in this thread. They are my favorite amps. I use EML XLS 300B tubes. With the Franks, my Altecs disappear with a floor to ceiling, wall to wall, soundstage. Big, realistic, sized images. Images are easy to "see" in front of you. You are there. Wonderful tone, albeit my Altecs can sound a bit strident at very high volumes (over 90db). This is with original 50 year old crossover capacitors that no doubt need to be replaced.

My 1.5 watt per channel SET 45 amps are also very good with my Altecs, but they have a little less flesh on the bones compared to the Franks. It’s nice to switch these in once in awhile.

My OTL monoblocks are just okay, very clear sounding but somewhat analytical.

Each of these amps are very quiet with the Altecs. Low noise floor, no buzz, hum, or hiss.

@pdreher 

I acquired the Franks about a month ago and the Music Reference RM9 MKII has been sold to a good home. The Franks have proven to be a better match for the Altec’s, as they allow me to hear deeper into the music.

Hearing deeper into the music. I understand. 👍

Charles