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Registered Member #76
Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458
within the next weeks i want to build my third vttc. the only problem i see is to get useful tubes for this job, a good one is so hard to find. i had a look on a few websites to find a tube. now i want to know if i can use one or two gi15b1 triodes , they are relatively cheap and can handle around 100watts each. its not going to be a large vttc so 200 watts would be more than enough.
heres a datasheet of the tubes i want to use, i can get one for around 4$
for the transformer, the tubes can withstand 1kV maybe a little more, so i cant use a mot, but thats no problem, im expierienced in winding transformers in the low KV range, so a 1kV Transformer should be easy to build.
what do you think, can it work or is this tube totally unuseable?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
One thing you could do is compare this datasheet to various tubes that are already proven for VTTC use, such as 811A, 810s, 304TLs, etc... and see if the specs come even close to match.
Did you check EBAY for tubes? 304TLs usually go for not too bad of a price.
I'm planning on building another tube coil in the near future as well. I have two original RCA 810 tubes never opened. Should be a beaut!
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Just a comment on the 304TL that Dan mentions. I wouldnt try to buy them, they are all very old and the filaments are very brittle. Most of the 304's that i bought were destroyed in shipping. I did get a couple good ones, but ended up destroying a working one myself when i bumped into the wooden base where the tube was mounted (filament just fell apart).
Go with more recently made tubes. 833s are very popular for VTTCs for a reason. Very rugged tubes and can process lots of power.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
I would recommend the 811a, those things will work for coils with input powers up to 1kw, and will take plenty of voltage in... (i have run them at >4kv with no arkovers). They are cheap ($17 buy it now on ebay), robust, and there are a lot of designs based around them...
Also, they work well for small vttc's, the first (or the third depending on how you count it, I just kept changing pieces of one) one I made uses a single 811a and a mot (with full 120v in) with a 2.7" by 5" secondary that gives beautiful streamers about 4" long from an 8" by 8" footprint, and about 12" tall.
Registered Member #76
Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458
thank you guys for the help. i had a look on ebay and found a 811a for around 19€ from england. i think i´ll buy one.
i have a mot lying around and all the other parts i need as well (resistors, doorknob caps etc)
thank you, that will be a nice project
hehe, now i can get serious
i got a eimac 4-250A Tube for a good price seems like i have to go bigger
update
today i wound my filament transformer. cause i want to build the whole thing with tubes, i searched for a high voltage rectifier tube and i found a py88, which i want to use for the levelshifter.
now i have a question about levelshifters. first, i get 2x the peak voltage rating of the mot, right? but the tube is ratet at 4kv and i want it to be reliable, can the tube withstand the voltage or do i have to worry about tube arcovers?
what size should the capacitor in the levelshifter have? i only have a 1yF MO capacitor is this enough?
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
The 4-250A is a good tube and should handle the 5kV peaks supplied by the level shifter.
As to how much capacitance for the level shifter. That depends on the current draw. With my dual 833A coil i had to use 4-5uF usually. My smaller 304TL coil needed 2-3uF. Im guessing you will want 2 MO caps in parallel at least (1 will work, but it will probably limit your sparks to 10" or so). There is room for experimentation. Basically, the amount of C changes the RF envelope shape to some degree, and this will alter performance.
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questions for new vttc
