Originally Posted by Duggeh
1200V? Amazing
As for the 1950s design, thats no bad thing. The ESL57 has no shortage of fans today!
The original used -1550v for bias. It was quickly changed to + for obvious reasons and then it was lowered due to some changes in the drivers.
The Quad ESL is still a great speaker because it was simple and didn't try to be something it wasn't. Peter Walker was very adamant that the basic operating principle should be left well alone so no dual membranes, curved panels or other tricks that don't work. He did go a bit off track with the 63 but it is still a good speaker and the new ones are a great evolution. The drivers are from the 50's and while that isn't necessarily bad, the basic design was "stolen" from Janszen so no real development continued until much later. Not that there is much to develop in a square driver...
