Thanks. I've learned this lesson, and appreciate both moderators taking the time to warn and advise on this. It's logical, but I have had limited experience and particularly as it was okay earlier, I couldn't believe what I was seeing. I know, I should have. Fortunately, the heaters are still lighting up.
Before seeing that the circuit had been posted, I had traced the heater connections to those valves from the output valves. A gap in continuity showed that while the valve nearest the front is connected to the centre, the one behind it is not. I think this is the missing bit of this heater circuit. The inner valve should have a connection to the centre to either pin 4 or pin 5. I will now study the circuit diagram provided by roffe.
Thank you very much for posting it! 
As you say, there will be others who will be delighted to have it too.
