MegaTC

      13.8.2005 I though that I will not make any bigger TC because I don't have enough space for it. But once I had a walk I found laying 1,5 m long piece of nice 160mm PVC pipe so I decided to pick it up and make a mega TC ;). I cut the pipe to be 92 cm long (let the h/d ratio is 6:1) and though about a wire that I would wind on it. Such a big pipe would need a kilometer of wire or more. I had only some remaining 0,2mm wire that I used on BigTC but it was too short. I think that some 0,35 - 0,5mm wire would be optimal. Fortunately upcoming radio hamfest in Holice will be soon so I hope I will buy some wire there. And really I got some cheap spool of 0,3mm wire there. As usually I used my improvised winding machine made of a driller powered by variac and some support for holding the pipe. But during the winding I got a bad surprise - when I wound about 1/3 of pipe the wire had broken because somebody made a bad joke and put a layer of sticky tape inside the spool. Because I had the spool placed behind my back I didn't see it on time and didn't stop the machine. I'm a perfectionist little bit so I didn't accept any inhomogeneity in the winding so I rather removed it and started again. But when I wound off entire spool I had covered only 2/3 of my pipe - that damned 1/3 of wire I threw away was missing now! This pissed me off...

      1.10.2005 I was thinking if I should leave the winding as is and cut the pipe or unwound it and start again. I wanted to keep original design so I decided to do it again. I had a luck and bought quite big spool of 0,355mm enameled wire. I guess there was about 3 km of wire on it so I could wound this pipe twice. New winding process was done without problems and I wound entire pipe. Then I varnished the secondary coil by acrylic spray as usual I did on other coils. Here are some photos of the tiring winding process:


      2.3.2006 New secondary coil was idling in a pantry for some time because I didn't have a free time and I couldn't get some piece of bigger pipe for primary coil. Then I finally got a piece of 250mm PVC pipe from my friend. Maybe 300mm would be better but one meter of such pipe costs about 600 CZK. I wound 37 turns of insulated wire with 4 mm² profile as a primary winding on the pipe and 17 turns of 0,5mm insulated wire above the primary winding as a feedback coil. I plan to use this primary coil for VTTC powered by 1 or 2 GU-81M tubes. More details about windings you can see here.
      Because of higher weight of these coils I made the base board of 18mm chipboard instead of my favorite plexiglass. To make a manipulation with MegaTC easier I mounted 4 small wheels on the bottom side of the base board. Primary and secondary coils are not mounted in a hard way but can be removed easily. This will be good for transports or when I will need to replace primary coil accommodated for different kind of driver.

     

I calculated that resonant frequency of the secondary coil is 107 kHz and then measured 120 kHz. Currently I missing a suitable resonant capacitor for primary tuned circuit. It should be ~ 7 nF / 10 kVAC or some suitable smaller capacitors that I could wire into a MMC. I hope that I will have a luck and buy them somewhere. I'm forward to the first light. I'm curious about spark length compared to my previous smaller TCs at the same input power.