Amplifiers
Lots of people ask about which amplifier to use with the LS3/5A. The loudspeaker was designed to be used with amplifiers rated at a nominal 50W into an 8 ohm load. Because the LS3/5A has an impedance of 15 or 11 ohms, the power delived by a 50W amplifier designed for an 8 ohm load will be somewhat less than this, about 27W into 15 ohms or 36W into 11 ohms.
Any good quality 50W per channel amplifier should work fine. The LS3/5A is an easy load to drive. Higher power amplifiers can of course be used with care! The B110 makes a cracking sound if the cone hits the end stop and this usually results in the user diving for the volume control before any damage is done!
I use a pair of Quad IIs primarily because I like vintage tube gear, especially Quad. The II might at first appear a bit under-powered at 15W per channel. In practice they usually deliver a few more watts than specified and the combination works well.
As well as Quad solid state amplifiers, the BBC used many AM8/12 monoblocks manufactured by HH Electronics. The AM8/12 is rated at 30W into a 15 ohm load with a transformer balanced input. Sensitivity is adjustable up to 25V input for full power output.