Proac problem: tweeters or crossover?

There's a couple of things to consider here. The first is that the new tweeters are going to break in, and will sound different when that happens.

"I'm using Synergistic Research Signature 2/3, and I've hooked both the thick and thin runs of cable up to both the tweeter and the mid-woofer binding posts, individually, to confirm that everything's running as it should."

Those are 2 runs of completely different cables, they're not just thicker. Different materials are used. You need to try the speakers with either 2 runs of the exact same speaker cables, or 1 run and use the binding post jumpers.
Those cables that you have are a band aid type fix for a speaker with a very harsh tweeter like B&W. You don't need that with the 2.5's.

It wouldn't be a bad idea to list your entire system.

I recently had some Proac EBS with no tweeter output. The Solen caps in line with the tweeter had failed - very unusual for a polypropylene cap.

Zd542,
"Break in" for tweeters…Really? I am sorry, but please don't provide such advice when clearly you know nothing about how electronics or transducers work.

Twoleftears, this is exactly how normally properly functioning tweeters sound when operating w/o a woofer.

"03-06-15: Bojack
Zd542,
"Break in" for tweeters…Really? I am sorry, but please don't provide such advice when clearly you know nothing about how electronics or transducers work."

Sorry about that. Can you tell me what line of speakers you design? You didn't say.

Twoleftears,

I forgot to ask in my other post if the new tweeters are exactly the same as the ones you took out?

Twoleftears, as you may be aware tube amplifiers having output transformers should not be operated without a speaker or equivalent load being connected, especially when signals are being put through them. Assuming you are still using the Cary SET amp listed in your system description, it occurs to me that when you connected the amp to just the high frequency section of the speakers you were running the amp unloaded across those parts of the spectrum where the great majority of the energy of most music is concentrated. I say this given that the crossover point of your speakers is a bit higher than 3 kHz, as shown in Stereophile's measurements, and the rolloff of the high pass part of the crossover below that point appears to be a fairly rapid 18 db/octave.

Which leads me to suggest two things:

1)Don't do it no more :-)

2)I'm not certain of this, but it seems to me to be possible that the anomalous sonics you heard when only the high pass sections of the speakers were connected might have been the result of amplifier misbehavior resulting from the improper loading. So I'm not sure that any of those observations were meaningful.

And perhaps the differences you observed with the new tweeters vs. the original ones were simply due to what would under normal circumstances be inconsequential differences in their parameters.

What I would suggest is that with a little Googling you should be able to find a test record or CD you can order which has a set of 1/3 or 1/2 octave warble tones, or something similar, the set of tones covering the entire audible spectrum. That would allow you to very readily tell whether the tweeters and their associated crossover elements are working properly or not, which I don't think any of us can say at this point with any certainty.

Good luck. Regards,
-- Al