Quad 2905

I thought the original speaker, aka the '57 required a constant charge- and that the later models didn't. But I can dig down a little. 
Are these the models that were manufactured in China? There's another recent thread on here about panel failure due to the glue. 
I used to keep mine- both the '57 and the '63 plugged in 24/7 but different speaker. More if I find an answer or if someone else with knowledge of this Quad posts here. 
Yeah, typos, the bane of my existence.  And auto-correct makes it worse sometimes....

I did a little poking around and found the manual, as you say, it doesn't address the issue. FWIW, Kent McCollum, who rebuilt my '57s, had this to say (not on your model but on the difference between the 57 and 63 as regards charging the panels): http://estatsolution.com/faq.html
As mentioned, there was a thread here recently about panel failures which attributed cause to the glue. I can't imagine that turning them on and off is going to make a difference if that is the real source of the problem, but I'm speculating. Might be worth try to talk to a rebuilder- I don't know if the manufacturer retains the know how they once had- it has been a long time since I dealt with the company, though I did get to meet Peter Walker many years ago!