DIY REPAIR OF "BD-10" VIOLET WAND
VACUUM LEAK TESTER, QUACK TESLA COIL
2015 W. Beaty
These handheld Tesla Coils from the 1950s are still being
made, and repair-parts are still available. Today they're commonly used
in physics and chemistry labs, science
classrooms, and also used for finding pinholes in plastic tank liners.
They create ozone and UV light, and are still found in use for skin
treatments in some beauty parlors and barber shops. They originated in
1905 from the quack-medical arena, where they were claimed to cure
everything from baldness to diabetes to cancer. Today (2015) the new ones
cost $250 and up, but you can still find many antique versions on eBay.
(After you've repaired these one or two times, you can buy cheap dead ones
and get them working again.)
Secrets of disassembly
- Make or buy a custom 5/16 nut-driver
- Remove the nut found deep inside the HV socket
- Remove (unscrew) the plastic adjustment knob from its brass screw
- Dig out the brown sealing wax from two brass screws on the flat base
- Remove the two screws
- Unscrew the entire Bakelite upper half
- Push out the buzzer assembly Be careful not to break thin wires
between two coils
The small nut inside the HV socket is 5/16". However, the inside
diameter of the HV socket is under 7/16", much narrower than any nutdriver
tip's OD. This custom tool can be bought from
Electro-Technic, or you can make your own by grinding down a standard
5/16" nutdriver's tip to under 0.42" 0.D.
Plastic adjustment knob
(*) The plastic knob on the adjustment screw is sometimes too tight to
remove. Try turning it
CCW (all the way out,) then twist hard so the plastic knob unscrews from
its threaded post. If it's more than finger-tight, you'll need thin
needlenose pliers or a small 11/64 wrench. Use one of these to grasp the
flatted brass screw-shaft below the knob, then twist the knob CCW by hand
or with pliers padded with paper towel. Don't squeeze the bakelite knob
Main Assembly Stuck!
(*) Sometimes the main assembly will not budge from the bottom plastic
cylinder. It's a common failure: the wax capacitor adjacent to the 120V
buzzer drive coil has melted, and glued itself to the inner surface of the
Bakelite. Often it's possible to force a thin steak knife into the gap
between the plastic and the wax glob. Work it along until you can pass
the knife entirely around the main assembly. That frees it up.
HOW IT WORKS
See a typical schematic.
- The AC drive on the lower coil will keep the small iron slug
- First, the vibrating contacts are open. This lets the AC
supply-voltage momentarily charge the wax capacitor, max 160V at peak.
coil is in series, so the current and magnetism is building up there.
- The vibrating contacts close. This connects the wax capacitor to the
few-turns Tesla primary. A large oscillating impulse appears, with path
through the wax capacitor and the Tesla coil primary.
- With the contacts closed, the Tesla primary is providing a path
between the 120VAC
power supply directly to the vibrator coil (since the Tesla primary acts
like a short circuit for 120VAC. It's inductance is tiny.) The AC drive
then kicks this coil, keeping the vibrating contacts going.
- The high-freq oscillation in the Tesla coil primary is driving the
Tesla coil secondary. Extreme high voltage appears between the AC neutral
wire and the hollow metal connector in the end of the device.
- The high-freq HV oscillation dies away. The contacts open. This time
there was a large current in the vibrator coil, so with open contacts
removing the short, the
coil dumps its stored inductor energy into the capacitor, charging it
well above 160V.
- The cycle repeats, but with much higher voltage on the wax capacitor.
- [Note that the AC line has a direct metal path to the Tesla coil
terminal. If the AC hot and neutral connections got reversed, any metal
object stuck in the socket becomes a 120VAC electrocution hazard!]
A BIT OF HISTORY
These are the last of the quack-medical violet wands, the Bleadon-Dun
Model Ten "Violetta." The brown phenolic case even still reads BD-10.
These were saved from the 1951 FDA banning because all kinds of
professional scientists and neon signmakers were using them to ignite
plasmas in glassware, detect pinhole leaks in vaccum systems, or to serve
as an inexpensive pre-built Tesla Coil for various instrumentation and in
university classrooms. After Bleadon Dun Inc was no more,
Electro-Technic products, Welch Scientific, and Chicago Electric
Scientific Co. were selling them. Yet, the "alternative health" pamphlets for BD-10 can still be found, with claims to
be cures for alcoholism, arteriosclerosis, cancer, TB, diabetes, deafness,
epilepsy, whoopig-caugh, warts, and of course brain-fag (fatigue.)
Here's the first one, the
B & B Coil of 1905, only $165 (so, over $4000 in 2015