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Re: Toob coil questions



Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 

You might look up my cousin, Matt Pujol, who is in the Fort Collins area..
He's a ham and has fooled with high power tube amps, and might be able to
help you out a bit...Should be in the book.

Filament temp is critical for most tubes.. check that voltage AT THE
SOCKET... Also, be aware that some tubes have significant electron
bombardment heating of the filament, so if you're running currents and
voltages that aren't in the usual range...

Measure grid current with a run of the mill analog meter in series with the
grid... Watch out for reverse bias on the grid (kills it right quick now,
because the grid starts to act as the "plate", and gets real hot, real
quick).


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, September 18, 2003 6:12 PM
Subject: Toob coil questions


 > Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
 >
 > Hi All,
 >
 > I may be an expert on some Tesla coil things, but not toobs 0:-p
 >
 > So I got this tube coil off E-bay that is really cool!!  Makes 16+ inch
sparks!
 >
 > http://hot-streamer-dot-com/temp/P9180017.jpg
 >
 > http://hot-streamer-dot-com/temp/P9180018.jpg
 >
 > Far easier just to buy one in my case rather than trying to figure it all
 > out from scratch.  I have been trying to figure it out, but I have some
 > questions:
 >
 > 1.  Grid current - Can one just use any DC ammeter in series with the
 > grid(s) (maybe need a bypass cap?) to measure this current?
 >
 > Apparently it is easy, but I just wanted to be sure of the real method
 > used.  I had to replace to original tubes since a blew one up and one
 > broke...  I got two new Svetlana 811A tubes that are working great
 > (http://rfparts-dot-com/ - super great place!!), but I was wondering if I
 > needed to recheck this grid current thing.  Svetlana tubes are said to be
 > "different" than "American" or "Chinese" versions of the 811A.  An RF guru
 > at works says to always get Svetlana since they are the only ones that
 > "know" what they are doing anymore...  I was going to ask him about this
 > but he just had to fly out to Germany.   When I explained it shot 16 inch
 > arcs off the top, his eyes sort of glazed over with that "deer in the
 > headlights" look anyway...  The plates barely get hot enough to glow but I
 > really have not turned it up yet till I am sort of sure I will just not
 > blow it up due to something not being adjusted right.  I think the plate
 > current is probably right on since the place metal in the tubes just
starts
 > to glow hot now, but I am unsure if the grid current needs to be adjusted
 > with the new tubes.
 >
 > 1a  What should this current be for Svetlana 811A ?  I guess there is a
 > quiet DC current and an operating DC current?
 >
 >
 > 2.  Grid resistance.  There is a resistance to ground in series with the
 > feedback coil and the grid of the tubes.  Like R1 in this very similar
 > circuit (no SCR stuff) at the bottom of John's page (note sure if these
 > things have "official" names?):
 >
 > http://members.aol-dot-com/futuret/page3.html
 >
 > Right now that resistance gets really hot and I note a number of people
are
 > using big variable power resistors like Digikey sells.  That allows for a
 > lot more heat dissipation and I guess grid current adjustment.  So I was
 > just going to replace it with the big variable power type.  I was just
 > wondering if the inherent inductance in the big power resistors is a
concern?
 >
 > I would like to add an ammeter and make this adjustable.  I will get
 > Svetlana 572Bs if (when ;-)) I blow these up...  The 811A is out of
 > production now and the 572B is supposed to be even better...  But the
 > 811A's are cheaper ;-))
 >
 >
 > 3.  How long do the tubes have to heat up before plate power and all is
 > turned on?
 >
 > I think I blew the one tube up by not letting them heat up enough before
 > turning on power.  I also note that the heaters are very bright but I
think
 > that is normal for this type of tube...  I can check the heater voltage I
 > guess ;-))
 >
 >
 > 4.  Do I need the plate chokes and resistors like the schematic above has
 > in series with the plate connectors?
 >
 > "Plate chokes:  10 turns 14awg magnet wire wound on 30 ohm 20W
 > resistor."  Right now, it does not have these.
 >
 >
 > 5.  I note the "primary" has a big heavy inductor and big heavy tank
 > cap.  Are these "tuned"?
 >
 > It does not seem like they are tuned to the right frequency now (not
 > sure...).  Maybe they just have to be "sort of close" since these coils
 > tend to self tune?
 >
 >
 > 6.  I imagine the feed back coil produces enough voltage on the grid to
 > make the thing turn on and off (oscillate) within the tubes operating
 > curves and all?  Any insight into that?
 >
 >
 > 7.  Sometimes it seems like the thing has a little trouble getting
 > oscillation started.  This may just be because I don't hear it breaking
out
 > yet or something too...  But if it has trouble getting the oscillation
 > started, is there something I can play with to help that?
 >
 >
 > When the tube blew up, it tripped out my $4000 tek scope, but the scope
 > protected itself (thank goodness!!).  But I have beefed up the input stuff
 > with some MOVs and all to help protect other stuff on the AC line.  I
think
 > these coils could use a little study into the fault protection and
 > optimization areas.  If anyone has any thoughts as to how tube coils could
 > be improved or studied, maybe I can help?  I am definitely no expert on
 > tube stuff, but I do have the equipment to checkout just about anything
here...
 >
 >
 > As you can see, "I know nothing"  0:o))  so any advice, tips, insights,
 > links, and answers are welcome!!
 >
 > Cheers,
 >
 >          Terry
 >
 >
 >
 >
 >
 >