Jeff Mullin's   

Single 833C Tesla Coil

Story by Dr. Hankenstein

    Jeff always wanted to build a Vacuum Tube Tesla Coil, so in the spring of 2007 he had gathered enough parts to begin the project. Jeff approached the idea like many of us do; that is: Get an idea what you would like have, then start gathering the parts. This process could take some time due to the many variables involved. Some parts are expensive, others hard to find, but once he was  ready to rock and roll...there was no stopping him! Jeff ask Dr. Spark and myself many questions throughout the decision making process. He chose to make his first coil not too complicated. It would also need to perform quite well and provide hours of experimentation and fun. The 811A coil was a bit too small, a dual 833C coil like Dr. Spark's was too expensive, so why not try a single 833? 

 

Arranging the Parts

(Please click on pictures to enlarge)

2 x 1.05uf / 2kv caps 

4 x 5k / 100W Grid Resistors

MOT and Coupling Caps 

Level Shifter Diode Assembly

Plate Meter Shunt Resistor

Plate Meter

Filament Supply

RF Deck

So there it goes for the rough layout.

    Unfortunately there was trouble in paradise: At first light the coil performed miserably. Jeff though he had smoked the 833. He came over to the lab to have me take a look at it. I had some spare tubes, but was unable to make the coil work. Only about 3" sparks or so. I hadn't any experience with the 833's; only the smaller 811A and 572B's. Jeff packed up the coil and went over to Dr. Sparks' garage. Dr. Spark had previous experience and luck with the larger tubes. Dr. Spark noticed right away that Dr. Mot was using a coil designed for a small spark gap coil....a poor match for a VTTC. So the primary and secondary were replaced with a new one and a special vortec accelerator was installed. What a difference! 21" Sparks! Way to go Chris!

Vortec Accelerator

21 Inch Sparks

 And Now For Some Sizzling Sparks!

 

A little Arizona Humor

"I was putting on a demo of my new single 833C coil...."

 

"All of a sudden I heard a really loud bang.....from my coil!"

 

"I didn't know what happened......It became really dark and I was scared....people came running from all directions to see the destruction..."

 

"I ran outside and discovered that the explosion had created two Dr. Hankenstein's!..."

 

"After the lights came back on, I found the problem: A bleeder resistor had flashed over and exploded...."

 

"Shortly after the authorities left, I became an instant celebrity!...I was famous! The news people wanted me to tell the whole story on how I caused a 50 mile blackout affecting three counties!..."

 

Disclaimer

Although the above was a fictitious rendition of the actual event; serious injury could have occurred. It was discovered that a bleeder resistor with a 500 volt maximum rating was placed across a high voltage filter capacitor. The resistor was properly sized for ohms and watts, but not for voltage withstand. The capacitor was charged to several kilovolts when the resistor failed.

 

Lesson Learned

Put several resistors in series or use a high voltage rated component when the potential exceeds the maximum part rating. 

Copyright Audiotesla 2008

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Important note about bleeder resistors

The incident about to be described could have had a very bad outcome, we were lucky.