Kat 6550 build (yes really!)

[Infinitely Baffled]

Hello, All. I wonder if someone can put my mind at ease about this. I am in the middle of building an old Kat 6550 kit that I have had for ages, and I am not too knowledgeable about the principles involved. You probably know the design employs 4 x 6550 valves and I am at the stage where I am wiring up the heater wires between the tag boards and the four valve bases. The instructions say to connect tag CL15 to pin 7 on each of the four valves bases, and connect tag CL18 to pin 2 on each valve base. That's clear enough. Because the two wires going to each valve base are to be twisted together I carefully used a continuity meter to ensure that I connected the correct wire of each pair from the correct tag to the correct pin. No problem, but once finished I did some testing with the continuity meter to ensure I had got it right. I found that all four pins 7 connected back to tag 15 (correct), and all four pins 2 had continuity back to tag 18 (also correct) BUT I was also getting continuity signals between the wrong pins and tags and also between pin 7 and pin 2 on each valve base. In other words, despite my efforts to observe the right tag to pin connections, it turns out that everything has turned out to be commoned up somehow. Looking back at the tag boards, whilst the soldering is not the highest standard, it is perfectly OK and I'm fairly confident that I haven't inadvertantly linked up tags 15 and 18. So I'm left wondering how the two separate circuits have come to be joined together. The only possible explanation I can think of is that the two heavy grey wires that run from the tag board back to the mains input transformer somehow join the two circuits. One of the grey wires is soldered to tag 16 (which is connected via a jumper wire to CL15) and the other to tag 17 (again, connected via a jumper wire to CL18). Now, I have no idea what goes on inside a mains transformer, but is it possible that the two grey wires and the transformer are somehow bridging tags 15 and 18, and with that the pin 2 heater wiring and pin 7 heater wiring? And if they are, is that correct, or is it going to end in tears when I finally switch on? Whew, that's a lot of information, and thanks for sticking with it to the end. What do you think - has something gone wrong here? Cheers and thanks. Infinitely Baffled.