KLH model 9 electrostatic Speakers

@jayctoy , ESL have always been amp sensitive (not power cord senstive) They are also a very reactive load and their impedance drops dramatically as the frequency goes up. By 20K they can be under 1 ohm.
This has destroyed many amps. Current demands increase with frequency. Many amps will overheat because of this. 
Back when JGH was reviewing the KLH 9's there were very few if ant high powered amps. Amps like the Crown 150 and Phase Linear 700 would overheat and self destruct. The best amps to use back then were the Marantz Model 9's and several Mcintosh amps. Today You would use a High power Class A amp with a lot of heat sink or an Atma-Sphere amp.
M60's would be perfect!

Mijostyn my Plinius sa 100 has no problem powering the nines. I get all the dynamics and musicality of the nines, my Norh monos sounds good on the Nines.How much power is the atmasphere  M60?

Today You would use a High power Class A amp with a lot of heat sink or an Atma-Sphere amp.
M60's would be perfect!

How much power is the atmasphere  M60?

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While the power of the M-60 is fine (about 60 to 80 watts) the high frequency impedance will cause the amp to sound rolled off, which it is not. To solve this a set of ZEROs (www.zeroimpedance.com) should be employed. With the ZEROs the M-60s will make more like 80 watts.

Ralph thank you for your response, I checked the zeroimpedance unit $1149 a pair. 

Ralph it looks like my Art Audio concierto 40 w will be benefited from the Zero impedance, I think the KLH need to be using 16 ohm.Thanks again...