Tube amp forethought

Btw, how many ESL models did Quad make, i found these:

57
63
988
989
2812
2912
2805
2905

Kg, it must be around 6 by now. The current ones are the ESL-2812 and 2912. They are now owned by a Chinese company somewhere in Shenzhen and they are made in China.  The 2912's are something like $14,000. At that money the clear choice would be the Sound Lab 545 which is about the same money but is a seriously better loudspeaker in all respects and it is made here in the USA. 
The first Quad was the 57 and you definitely want to stay away from those. They are way too fragile. Next is the 63 which is much more reliable than the 57 but some would argue do not sound as good as the 57. I think that is probably romantic brains talking. Then there are a few in the middle which have a good reputation but I have never experienced them so can not comment on their sound. By then I was deep into Acoustats and not really paying attention to other ESLs. Acoustat is out of business. You see them pop up once in a while. Most of them have been broken up into parts. They were relatively inexpensive and audiophile hobbyists bought them up and tried to rearrange them into speakers they thought would sound better. A clean pair of 2+2's would be a real snag.
Sound Lab speakers come up on rare occasion but most of their owners consider them permanent purchase. Where else you going to go?  

Everything you need to know about the  glass bottle.

http://ken-gilbert.com/images/pdf/taste_of_tubes.pdf

Good information and history. 

I have long assumed that when anyone used the term the QUAD ESL they were of course referring to the original electrostatic model Peter Walker introduced in 1957. All other QUAD modes are referred to by their model designation---63, 989, etc., even the reissue of the original (a while after that model had been discontinued), named the QUAD 57.

I would also suggest Atma-sphere amps.