If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #55297
Joined: Mon Jun 22 2015, 04:36PM
Location: India
Posts: 3
Hello! I'm a high-schooler from India currently working on finishing up a tesla coil model, based on Steve Ward's dual 811A schematic. I was hoping I could get some advice/help with it, is there anyone who could lend me a hand, please? I'm somewhat new at this, and I'd really appreciate any and all support from the wonderful members of this forum.
Please find here a document with a report on the Coil, I'd love advice. Thank you!
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
Welcome to the forum! I'm not quite sure what area you need help in. Do you want advice for the physical construction and tuning of the VTTC, or help with the theory of operation and math for the report?
If you need help with the construction, it will be very useful to post pictures of your current progress. With pictures we can see if anything needs to be improved or changed, it will speed up the help you receive.
In your report (haven't read it all yet) I noticed you were looking for a program to draw circuits. I'm currently using "TinyCAD" which is a small free program that's super simple to use. It doesn't have a vast library of symbols, but its enough for non-serious hobby projects.
Registered Member #55297
Joined: Mon Jun 22 2015, 04:36PM
Location: India
Posts: 3
@GrantX, thank you! Well, I sort of need help with both those areas. :P Thanks for the circuit advice, made my diagram which I hope is accurate — please find it attached. Build photos also attached, please do tell me if you want me to put a specific angle.
My current objective is to tune and test the coil — I need it to work at least once ASAP (preferably within the week), but I'm fairly under-confident of my own calculations and efforts. :/ I have connected the vacuum tubes properly (I hope), based on the manufacturer's guide on its terminals, and got the rest of the circuit ready. Even though I have studied theory, I'm still unclear about the purpose of the computer power supply, and also about whether using this on 240V supply (which we get in India) versus the 110V Mr. Ward used merits any changes to the schematic.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
1. How to connect the computer power supply
Your schematic is incorrect, that is, you have drawn the vacuum tubes with the wrong internal components. I cannot find a datasheet for "813A", but i can find them for "813", and it shows the tube has multiple grids which requires some extra components.
From reading the datasheet, we find that G1 (grid 1) is the main control grid, takes the same function as the grid in a triode. G3 is an "internal shield" which, for Class C oscillator is to be connected to 0V (ground). G2 has to have a voltage which tracks along with the plate voltage supply, this is simply accomplished with a resistor from the MOT output to G2. It is unclear whether there needs to be a capacitor to filter this voltage at G2, but if so, i think a value of 1nF with a rating of 3kV (small ceramic disc cap) would be OK. I would try without this capacitor at first. The resistance to feed G2 is not something i know, but the datasheet suggests no less than 5k ohms, and I've seen other VTTC schematics with higher resistance here for smaller tubes. I would think 10K ohms will work, but maybe some tuning can be done here to improve performance. Less resistance should allow more tube current, but too low of resistance could damage the grid and ruin the tube, so keep it to 5k or greater. I have attached a schematic showing 1 tube, you can figure out how to make it for 2 tubes.
I see you have the 30 ohm resistors already in circuit. Simply use 2 new pieces of wire (say 40 cm long each) and wind each piece around each resistor and solder the ends to the resistor terminals. The process and result should be very simple, you only need about 10-15 wraps of wire on each resistor. This coil will look like a "short circuit" across the resistor except at *very* high frequencies (10's of MHz) where this small coil will have some reactance. I have attached a picture demonstrating the construction. Wire insulation does not need to be thick (magnet wire would be OK), but the wire should be heavy gauge. I show a thin wire because this was just to demonstrate, but you should use something >1mm diameter.
Practically speaking, you could simply eliminate the 30 ohms resistors and inductors (just short circuit them) as they are mostly there to help protect the vacuum tubes if there was an internal arc-over between the plate and the grid.
Also, i noticed you are trying to solder connections to the tube, i would not do this! Applying heat to one small area (the contact) of the tube can thermally stress the glass to metal seal and ruin the tube. Hopefully your tubes are still OK. Tubes are meant to be connected with some sort of spring/clamp connection which clamps onto the pins without soldering. Also, a proper tube socket does not rigidly fix the positions of the tube pins, but rather, allows the tube pins to move slightly as the tube heats up and physically expands the distance between pins.
EDIT:
With a bit of searching, I found John Freau's suggestion for dealing with the 813 "extra grids", sounds easy and effective. I believe he is saying connect G2 directly to G1, and connect G1 to the rest of the circuit as usual. G3 still connects to cathode ground.
" Still trying to get this dual 813 VTTC going, with no luck. The main problem right now is figuring out what to do with the extra grids (G2 and G3) of the 813 tubes."
The easiest approach is to tie the control grid and the screen grid together and use the combo as the control grid. The suppressor grid should be grounded to the cathode.
If you want to run the screen grid separately, use a 40k ohm resistor of about 100 watts. It will draw some current in it's role as a dropping resistor. You want about 700 volts on the screen. These resistor values are for a single tube.
In my setup I used a level shifter (ac doubler) MOT and obtained 16" sparks without staccato from a single 813. Longer sparks are probably obtainable with some better adjustments. I show some similar schematics and stuff at my website at:
Registered Member #55297
Joined: Mon Jun 22 2015, 04:36PM
Location: India
Posts: 3
Thank you so much, Mr. Ward! I'll do those things.
The reason I had to put this 813 was that the website I designed the schematic on didn't have the accurate diagram, so I'll make one myself based on your super-helpful photo.
EDIT: the specs for the particular tubes I have seem to make them look identical to the 811As you used in your original VTTC, so I connected it accordingly, even though the schematic doesn't show it.
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
Considering that the wire-wound ceramic resistor is also a similar coil, should some thought be given to winding these "TWO" coils in the same direction??? The internal resistor winding direction should be simple to determine.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Dual 813A VTTC — based on Steve Ward's design: HELP NEEDED
