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Potential issues using low powered tube amp with electrostatic speakers

In a previous post I was requesting information concerning the operation class of a pair of tube integrated monoblock amps that I got as part of a trade. For purposes of this question, though, knowing that is probably not important. These amps were ordered by a local discriminating audio hobbyist who moved shortly after their delivery and we have no way of contacting him or the designer/ builder for details but here's what we think we know. The original said they were designed for class A operation.
The input tube is a 6EU7; the output tubes are 4 EL34's with 2 enclosed top mounted transformers with one smaller transformer inside the chassis. There is an off on power switch, a toggle switch of unknown function, VU meter and volume control pot. Because I've owned 2 Cary Audio amps that had switches to switch between ultra linear and triode (class A?) modes I'm thinking this one might be the same.

Now for the question; because I'm using these with Martin Logan Ethos speakers I'm concerned about high current demands with their dramatic fluctuations in impedance loading and how that may result in damage to these amps. I've used other electrostats (ML Odyssey) and Cary 808r amp which I very much enjoyed. I'm equally happy with this combo.
Any advice would be appreciated.
128x128broadstone
atmasphere's avatar
atmasphere
11,556 posts
 
Use the amp on the lowest impedance taps, 4 ohms in this case.

Martin Logans tend to be low impedance, often 4 ohms at the crossover point with the woofer, decreasing to 0.5 Ohms or so at 20KHz.
If the amplifier sounds a bit dark or rolled off on top, it may be the low impedance messing with it. You can correct this using a set of ZEROs (www.zeroimpedance.com).

You won't damage the amps in any event, at least no on account of being hooked up to these speakers.
bruce_philly
31 posts
 
I used big VTL 300 Deluxe monoblocks on Martin Logan Quest Z speakers (they have a cone woofer) and they didn’t work out at all. The VTLs are really big monsters.

The ML quests were known to be difficult loads on an amp. The sound was really not that good. I replaced the speakers, not the amps, and purchased a pair of Magnepan 20, top of the line speakers and the matching worked very well. I lived with this setup for about 10 years and was very satisfied.
What I found really interesting was the problem was not in the bass. That is what everyone told me would be the problem but it was not at all..... the sound was "glassy" in the mids and upper frequencies. I never heard this characteristic before. There is no doubt, it was the tube amplification. Before I purchased the MLs, I was traveling and when I would be in a new town, I would pop into a high end dealer and listen and quickly decided on the MLs. All the shops powered the MLs with transistor amps. I figured my VTLs were monsters so I would have no problem. Wrong.

Of course, after I described what I was hearing to my local stereo shop, the guy said "Oh that is the tubes, you can;t drive MLs with tubes"... Great.
A simple test is just borrow a friend;s transistor amp and compare for yourself.  The transistor amp does not have to be a big one, just a quality unit.... you will see (or hear).
Peace,
Bruce in Philly

atmasphere's avatar
atmasphere
11,556 posts
 
There is no doubt, it was the tube amplification. Before I purchased the MLs, I was traveling and when I would be in a new town, I would pop into a high end dealer and listen and quickly decided on the MLs. All the shops powered the MLs with transistor amps. I figured my VTLs were monsters so I would have no problem. Wrong.

Of course, after I described what I was hearing to my local stereo shop, the guy said "Oh that is the tubes, you can;t drive MLs with tubes"... Great.
You certainly can- I have had customers driving MLs with great success for the last 28 years, and we make OTLs! You use something called the ZERO (www.zeroimpedance.com). That gets rid of the glassy sound and opens up the highs.
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