Need 811a vttc tank cap. / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

Need 811a vttc tank cap.

1 2 next

Move Thread

LAN_403

Arcstarter

Fri Oct 17 2008, 03:51AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

I am making 811a vttc's and sellin' them and i need a good 1nf tank cap that will NOT die. I have a small doorknob 20kv 1nf tank capacitor, but in 10 seconds it gets too hot and loses performance and after 15 seconds the sparks disappear. I used a transparency capacitor i made and it worked great, but of course that will not last long. I would like a capacitor of about 40kv AT LEAST. I used the transparency capacitor and there was a ton of ozone so there is quite high voltages in the tank circuit apparently.... as well as current.

So, anyone know where to get one for cheap?

J. Aaron Holmes

Fri Oct 17 2008, 04:01AM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

I've actually heard only good things about the Chinese SrTi doorknob caps sold by Yish on eBay, i.e.:
http://stores.ebay.com/yishstore

Direct from China, and cheeeeeeap, cost-wise (well, compared to the TDK UHV's anyway).

If I ever get around to finishing my 572B coil, I'll probably use these.

Cheers,
Aaron, N7OE

Mads Barnkob

Fri Oct 17 2008, 06:43AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Hmm Im driving my dual 811A VTTC on a single 4nf 6kV (20kV pulsed) mica doorknob from 1969, and there is no problems with heating or decreasing performance at all.

I feed the tubes with about 3kV so the maximum the capacitor will ever see is about 10kV.

J. Aaron Holmes

Fri Oct 17 2008, 07:06AM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

The big transmitting mica caps generally get high marks for VTTC use, however they can be hard to find, expensive, bulky, and are often lower-voltage than the much cheaper and more available ceramic doorknobs. I know Steve Ward uses the SrTi doorknobs (TDK UHV series) in his VTTCs and he's said several times here on 4hv that he hasn't had any overheating. If you're not building a super-high-powered VTTC, the ceramic doorknobs are a nice way to preserve the "cuteness" of your project. Plus for the Yish prices, when one blows (unlikely) another one can just take its place; they're like shark teeth

Cheers,
Aaron, N7OE

Mads Barnkob

Fri Oct 17 2008, 08:59AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

I noticed in the ebay shop that he will lower prices on custom orders, but as we are all around the world, i guess the reshipping wouldnt make up for the small bargain we could get :)

Hazmatt_(The Underdog)

Fri Oct 17 2008, 09:03AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I use the TDK UHV 9A and UHV 6A caps for my bank, but I would go for the Yish store in this case too. I needed 40KVDC 2nF caps that were indestructable and MATCHED, but you really don't need a set of 20 or 30 matched caps so I probably wouldn't bother getting the TDK caps... that is unless you want to buy 5 at a shot for $100, it's pretty worth it to me, but we don't know your price range.

I generally pay $20 each for the suckers which is a pretty good deal considering they're $400 each new.

It all depends on what kind of reliability level you're looking for, selling points to the customer, power level, asthetics.

Steve Conner

Fri Oct 17 2008, 09:54AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Mica capacitors are always good for RF. Ceramics however come in two kinds, one good for RF and the other for DC blocking only. If you use the DC types as tank capacitors, they get hot and their capacitance changes wildly, throwing your coil out of tune.

So when shopping for ceramic tank capacitors, don't buy anything that doesn't have a kVA rating. (Or AC voltage and frequency ratings, which amount to the same thing as specifying kVA.) The DC block caps have a DC working voltage rating only.

Yish lists the two types as "High frequency power" and "High voltage".

Bamacoiler

Fri Oct 17 2008, 12:01PM

Registered Member #1628 Joined: Wed Aug 06 2008, 08:48PM
Location: Huntsville, AL USA
Posts: 95

I can also recommend the SrTi caps from TDK, Murata, and Yish. I have ran them all in a 833c vttc and after 5 minute runs they don't even get warm. They are awesome in my opinion and you can't beat the price on the yish.

Steve Conner

Fri Oct 17 2008, 01:52PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

So are you guys saying that the brown ones from Yish are good for RF too?

Bamacoiler

Fri Oct 17 2008, 05:36PM

Registered Member #1628 Joined: Wed Aug 06 2008, 08:48PM
Location: Huntsville, AL USA
Posts: 95

Well after 5 min run in my single 833c the 40kv 2000pf yish is cold. That's all I can speak for. Worked great for me.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob