Are "vintage" DAC's worthwhile, or is this a tech that does not age well

yep, good dacs from way back when will sound as good as good dacs from today

usual concerns about aging internal components, as for any aging electronic gear, should be checked out

then the add’l concern is input signal compatibility, esp. w r t higher res feeds used in more recent times

examples of mine in hand -

1 - 1997 vintage van alstine fet topp dac, with its lovely philips tda1545 r2r nos chip and 12ax7 output stage.... sounds as good as any $1500-2000 dac today - but it will only accept 44.1 khz input due to its crystal semi input chip of the day

2 - 2003 vintage modded musical fidelity trivista 21 dac w bb1792a dsd converter and 5703 mini tube output stage - it accepts all inputs and sounds as good, if not better than the current high dollar dacs out there - in fact better than psa ds, dena term, schiit yggy in terms of imaging timbre and holography

I don’t know how much of that truth, but audophiles say that the old (for example) Sonic Frontiers dac, is so well crafted that creating a similar-sounding dac would cost a lot of money to this day. Is there as much as it is true. Because these three I mentioned dac’s- are well known in the world, legendary. Or I’am not right?

You can be sure vintage DACs are good simply by the state of the huge vintage market, all the refurbished vintage DACs, the small cottage industry of artisans making beautiful wood cabinets to show off fine vintage DACs, and by looking at how many decades old DACs sell today for more money used than they cost when they were new back in the day. People just can't get enough of that vintage DAC sound, and they are willing to pay for it. 

Oh, wait a minute, sorry, my mistake. That's turntables. Vintage turntables. Old DACs people throw away. Sorry. Nevermind.

Oh, wait a minute, sorry, my mistake. That's turntables. Vintage turntables. Old DACs people throw away. Sorry. Nevermind.

Very “interesting” explanation about vintage DACs. Oh, wait, sorry, about vintage turntables.

MC you're a peach. :-)

LOL, I'll tell you what, I have a Krell 5.1 same time most of the HT preamps were both a HT system and stereo playback..

That HT unit has a DAC and stereo playback that will match a LOT of the newer units..  The gain stage is all class a, they are different..

Like my buddy says (All Krell and Martin Logan) "It's a Krell" he's not kidding.. I got my HT 5.1 from him for 200.00 12 years ago..  They have one of the best remotes EVER made. CnC from aluminum billet. I got to dig that out.. Great 3 speaker playback with sub control on the remote..
The remote sold for 350-500.00 LOL GOOD Buddy..

Regards