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[TCML] Re: Finally finalizing my 304er VTTC

Hi there, Dick!

I happened to be @ the Roger Smith Tesla-Fest where you gave him that big coil... I’m pretty sure that I have a photo of it somewhere...

The 4 to 6’ discharges from the VTTC you referred to are unbelievable!!!

What was the power source and how many 304-TL tubes were used?

Bill Fix

Sent by Mačak's humble servant.

> On Apr 25, 2021, at 6:29 PM, hooverrl@xxxxxxxxxxxxxx wrote:
> Hello Chris,
> I have an old coil that runs directly from the AC output of a Thordarson 1500 VAC plate transformer (300 mA). It runs on 120 VAC. The circuit does not use the diode and capacitor voltage multiplier that you are running. I have a single 811-A triode for the oscillator. The primary has a second tickler coil for feedback to the grid. The secondary is 18" of close-wound #22 heavy Poly-Thermaleze (formvar) magnet wire wound by hand on 2" ID PVC pipe. With no top toroid (just using a 1/4-20 on a through-wall insulator). I get single dancing brush discharge up to 6".  Originally, I didn't seal the ends of the PVC and it arced down the inside of the pipe and burned a serious black trail, so I had to make another secondary. For the replacement, I sealed both ends closed and have had no further problems with arcing inside the PVC pipe.
> "304" - I asked about your application as I used to run a LECO carbon tester at work. It ran on 120 VAC, but maxed out at 22 amps. It was an 18 MHz induction furnace. A three turn primary would turn a crucible of iron filing red hot in 30 seconds. Co-worker and local HAM Ed Smith (RIP), used parts from one of the old furnaces for his Tesla Coil. He just changed the primary and added a big secondary. With a high voltage ring (from high tension work) he could get 4 to 6 ft continuous brush discharge for intermittent use. He swore by the twin 3B28's for his rectification. The third tube looked like yours, but was the 304-TL. The circuit was enclosed in the original induction furnace steel enclosure with two large cooling fans. The running fans were nuisance noisy, but bearable to be around when running.    
> Have you been to Roger Smith's Tesla-Fest in Chillicothe? I gave Roger one of my other secondaries with elephant stand primary. We have movies of both his big coil and the one I built (which has spaced secondary turns like the original coils that Tesla built.) 
> Remember to use your discharge stick when approaching the coil after use.
> Dick Hoover
> -----Original Message-----
> From: Chris Reeland [mailto:chrisreeland@xxxxxxxxx] 
> Sent: Sunday, April 25, 2021 12:41 PM
> To: tcml@xxxxxxxxxxxxxxx
> Subject: [TCML] Re: Finally finalizing my 304er VTTC
> Hi Dick and all,
> To answer the first question:
> And give some VTTC basics for those that do not know...
> And possibly clear up some (but not all) of the "mysteries" of these
> VTTC's...
> The most common VTTC oscillator circuit is self rectifying when feed with
> AC. This ends up being half wave as the power/oscillator tube can only
> conduct on positive cycles. So it basically has equal on/off time periods
> since off on negative, so overall current draw is lower and everything runs
> cooler.
> When rectifying full wave (center tap type or bridge type), the power/osc
> tube will now conduct near nonstop with the slight exception of the very
> short trip back to 0 then right back up because of ripple. Current draw
> goes up of course and everything tends to run hotter.
> If you filter this full wave output to smooth ripple, the power/osc tube
> now runs nonstop and so does current and again everything tends to run
> hotter.
> And now finally answering Dick's first question :^)
> Technically no, on AC power.
> It is a level shifted supply (or this is sometimes called a DC restorer).
> This output waveform is all positive with twice peak input and of course a
> lot of ripple here. It does have a longer period of falling to 0 and back
> up compared to full wave, but it is not much overall. Because of twice the
> peak voltage, current draw goes way up of course and in most ways,
> everything tends to run hotter just like full wave. My level shifter is
> currently set up with a solid state diode and a charging capacitor, which
> is the method used on VTTC's by most builders for the level shifter when
> used.
> Now this level shifter is a form of a voltage doubler, but we do not want
> to use the "traditional" voltage doubler circuit. We want this one with the
> "horrible" amount of ripple. This positive waveform has very nice long 60hz
> "ramps" that should be taken advantage of with an add on circuit. In my
> opinion, this should not be run full CW on VTTC's for very long. Everything
> gets hot quite fast, the same as full wave (I have experimented in the past
> with full wave without filtering).
> We really should take advantage of these nice long ramps with an
> interrupter circuit which "switches" the cathode of our power/osc tube at
> the right time. I have found that our traditional interrupter circuits are
> "switching" in late when used on level shifter supply. This traditional
> interrupter circuit was originally designed for normal AC input as the
> trigger part of the circuit is off a normal AC waveform. While this does
> work some for level shifted supply it is not optimum, as I said it does
> switch late. I have been experimenting with these the past couple of years
> and learning of a few different ways to better switch for the full extended
> ramp time this level shifted supply waveform offers. At lower break rates
> in interrupter circuits, this achieves the best longest, straightest swords
> that many desire, including me :^) This does make a difference.
> And as many know, these interrupter circuits are great for...at reduced
> break rates...for everything to run much cooler, which means greatly
> extended run times :^)
> But a word of caution...as you increase break rates with this circuit...you
> are now once again approaching full CW... which means more heat and
> possible problems if things pushed too far...as can be seen in my acrylic
> tube.
> Please correct me if anything is wrong here, but I think I have everything
> correct as I understand it. I can take it from everyone...if something is
> not right :^)
> And now to finally answer Dick's second question. I am really good at
> stalling... ain't I  :-D
> No, I am not using a pair 3B28 xenon gas diode tubes in a full wave center
> tap. This MOT transformer already has one side of the high voltage
> secondary inner wire attached directly to the transformer core, so at
> ground potential of course and I am using the above mentioned level shifter.
> I do have several of these gas diode tubes and other mercury vapor tubes
> and a few high vacuum type diode tubes. But I have a problem of finding the
> required low voltage, but very high voltage insulation type filament
> transformers. I only have 2 that I have gathered over the years in my now
> "mountain of junk". They do not come by very often these days. Seems, when
> they do, the seller knows what they have and I can not justify the high
> price. I often wonder where heck they all are, unfortunately I think many
> got scrapped over the years.
> So even though I am "mainly a VTTC tube guy", I am using a solid state
> diode in the level shifter for a few reasons. One high voltage insulation
> filament transformer I have is a 10V 10A  and has no nameplate on voltage
> insulation spec, so it is just a guess on it. Also it is quite large and
> heavy. It is 4-5 times larger than a regular 10V 10A filament transformer.
> I do have a transformer for 3B28's, a 2.5V with 10,000 volt rated
> insulation, but again quite large and also an unfriendly 240V input, so
> another added transformer would be required for 120V input and another
> variac(I like to have a variac to control filament supply).
> For this coil build I want everything as light as possible and 120V input
> and very easily portable.
> So...I have a solid state diode...still have the main tube of course :^)
> Ok... some damaged coil measurements coming out of curiosity and will post
> when I can...back to work here on this project.
> Chris Reeland
> Ladd Illinois USA
> Sent from my Samsung Galaxy Tab® S
>> On Sat, Apr 24, 2021, 4:54 PM <hooverrl@xxxxxxxxxxxxxx> wrote:
>> Chris, are you running your VTTC 304 on AC power? Or are you using a pair
>> of 3B28's for a full wave rectifier first?
>> Thanks,
>> Dick Hoover
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