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This was my first coil and in the true beginner's tradition it was mainly constructed from stuff that was lying around the workshop.




1: Hanging around waiting for the time it was needed.
As this is the most delicate part, hanging it up seemed the safest way to protect it from getting any damage, and is still the method I use today.






2: Primary was stored under the bench with the toroid.

The toroids, made from aluminium ventilation duct, are easily dented.






3: The main part of the old coil sitting in its 'kennel'.

The curtain dropped down and all the dust was kept out. Dust and high voltage can be a bad combination, especially if the dust is conductive.






4: This old toolbox originally housed two 10,000 volt 50 mA NST's.

Originally the coil was designed and powered by a single NST which was housed in the box that is the base for the coil. The I progressed to using two NST's, then to four, before building a transformer. Finally I end up with a PDT or Pig.






5: The NST output plug's were simple 'banana' plugs that pushed into corresponding terminals on the Terry Filter, making a quick easy connection.

All four earth leads (NST, Terry filter, Strike Ring, Base of secondary) simply bolted together with a wing nut onto the main RF earth cable.







6: Ready to go.

The four uprights supported the primary coil deck that just dropped onto the posts. The MMC was then a single sheet of 0.5 inch Acrylic. This was strong enough to take the secondary and toroid weight.






7: NST plugs (see 5 above ) were plugged in and ready to go.

The thick blue lead went from the capacitors down to the spark gap, which was located inside the box that formed the base.





8: The two NST plug's connection into the Terry Filter.

These leads are not using correct high voltage wire, so they needed to be kept apart. The current they carry is only 100mA, so this type of push-in connection was sufficient.






9: Ready for the primary to be dropped on.

The primary located on the four plastic studs (circled in red) sticking up in the end of the acrylic rods. The secondary then screwed onto the central threaded stud (circled in blue).






10: The primary just dropped on.

In its base it had four holes that aligned with the locating studs mentioned above.





11: The primary is in place and you can just make out one of the locating studs (circled).





12: The connection that went to the inner coil of the primary.






13: This just tightened up by hand using the large knurled nut.






14: The circled mounting post is where the lead from the outer of the primary fastened onto.
This completed the connection onto one side of the MMC.





15: The lead (circled) is now in place.

Again a knurled nut was used that was easily hand tightened.






16: The main spark gap was inside the base at the bottom.

This had an airtight cover and can be seen in more detail HERE.
This cut down the spark gap noise significantly. Adequate air cooling took care of the heat issue.






17: My first attempt at the outer (movable) clamp (tapping point) on the primary

To move the clamp a short distance you simply unscrewed the bottom bolt a quarter turn, allowing the clamp to slide. This bottom bolt is also the connection for the other end of the lead shown above in 15.
To move into a different section (the primary's deck is split into 6 sections because of its mounting combs) you need to undo the two knurled top nuts and open the clamp up (see below).






18: Inside there was a little brass 'shoe' that made the contact.

This was free to move up and down in the surrounding acrylic, and was pushed hard against the tube by the bottom bolt.
Although this made a very good contact, it proved too fiddley on a dark night with cold hands! For this reason I made the one shown below.





19: The second attempt at a primary clamp.

The original one was just too fiddley on a dark night!







20: This short piece of studding that screwed into the base of the secondary allowed one to hang it up easily (see photo 1 above).






21: Once the studding above was removed, the secondary then screwed onto the mounting post.

The post was able to be raised up and down to alter the coupling factor by removing a pin and locating in different holes.






22: The secondary partially screwed on, and then shown fully home.

The electrical connection to the RF earth was made through this mounting post as well.





23: This half inch aluminium rod at the top end took the toroid.

The toroid was a simple push fit.







24: The underside of the ridged toroid showing the locating brass bush.
All my toroids have had the same mounting arrangement.





25: The fully assembled 4.7 inch coil.

The two suction pipes for the sucker gap can be seen either side. Also the front cover is now in place. The black plastic thing in the front cover was the air inlet pipe. It was just a coincidence that it bore an uncanny resemblance to an old Hoover brush attachment.