New here to diyAudio. I appreciate the wealth of information and knowledgeable experts here. I recently acquired a pair of Acoustat 2MH's. I've been a big Acoustat fan for 40 years since I got my first set of Model 2's in the early 80's. I haven't yet had a chance to dig into the MK-131 interfaces (the speakers are fully functional), but my question concerns Preventive Maintenance. I want to do as few modification as possible. I understand the "C mod" is highly recommended, but I would prefer to keep the speakers as original as possible. So, my question is this: From the schematics I've seen on here, it seems that there is a single electrolytic capacitor present in the interface. Am I correct in assuming that this electrolytic cap is the only component prone to age-related failure, and therefore the only component that I should be concerned about replacing (given my desire to make as few changes as absolutely possible).
Thanks for you time.
Thanks for you time.
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I suppose it's a matter of opinion. I have both and ime the Monitor 3 easily beats the Model 3. Mind you progressive upgrades to the interfaces make an improvement I don't have the experience to detail. I have blue medallian interfaces however my direct drive amps also have upgrades. Imo the OTLs are in a completely different league to even compare. Much bigger and more life like sound. I started a thread here a while back you may be interested in...'isobaric esl alternative', where I talk about my current set up.
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Many years ago, I owned a pair of Model X. My memory may be clouded by the golden mist of times past, but I still remember being stunned by the bass they made and the effortless midrange that went with it. I replaced them with 1+1 for practicality but still remember the OTL fondly.
take a look at the trouble shooting guide in the manual. easy to find online. I have not matched tubes and no issues at all. I have changed entire unmatched sets. However I have only had a single tube actually fail with only diminished output as a consequence. I have read if they fail catastrophically, they can take out other components with them. I don't wait that long so I have a bunch that need to be tested. 
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How are you powering the amplifiers? If you are using a step-down transformer from a 50-Hz main, then the designed-for-60-Hz transformer might make some extra noise, and generate a little extra heat. Tell us more about your set-up in regards to mains voltage and how it is applied to the amplifiers. Or is this a new problem that developed in a properly working system?
Thanks for your help. The problem was a passive preamplifier with ground connection. Solved!
Hi I'm in Australia and I managed to pick up a set of spectra 11s (I think they have 1100 drivers though as they have the larger dust cap that looks like the 1100s) One of my woofers has unfortunately blown its voice coil and I dont know whether to get it rewound somewhere or is there a suitible model I can order online from somewhere that has similar specs Im not sure what to do. Any suggestions from anyone who has tried to recondition or replace thier drivers would be greatly appreciated
I would have the original redone. If you do replace the woofer, you'll need to buy (2), one for the other speaker also or they won't match. Also, a single new one will need to break-in. Not sure if they would ever match in that aspect?
"C" mod would be the place to start. Read back through this thread to find the info.
Hi Audio Adrenaline, I haven't used that amp, but am currently using an NAD C275BEE which seems to be slightly lower power spec on the most difficult to drive semi-medallion C-mod 6kV superslim 0.88+0.88s (homemade 1+1s using leftover 8" panels) and it drives them exceptionally well. Absolutely stunning bass in a smallish room for only 8.5" wide electrostats.
I was an NAD (and Acoustat) dealer back in the day. The 208 is stable into a 2 ohm load and seemed to be a good match at the time.
It is a little weak in the bass (control) and more forward sounding than I prefer, but was able to drive all the models quite well.