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Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Dr. Spark wrote ...
Herr Zapp wrote ...
Goodchild -
You mentioned that your QCW coil uses a single 10nF, 10kV mica capacitor. In the world of mica transmitting capacitors, .01uF at 10kV is a rather unusual rating, hinting at a physically very large capacitor.
Is this a G-series capacitor, with a cylindrical ceramic housing and cast aluminum end plates? Or a cylindrical CDE cap with cast-epoxy case? Or something else?
Can you post a photo of your cap?
Here is what these juicy caps look like, a few ended up in Steve Ward’s QCW coil @ Cheers, Mica Man!
Strange, I seem to have a cap in my QCW that looks exactly like that.... I wonder how that happened....
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
Hi Dr. Spark, are you sure those are mica caps for sure, they might be film caps? Not that that is a bad thing but I would like to know if a QCW could use a film or does it have to be RF rated? mica transmitting caps are generally RF rated, I believe because of there low dissipation factor. why not use Russian door knob caps. I have seen them in Rf amp tank circuits. I have received a couple of thumbs down for them. The caps in Dr. Spark's picture have a 100KHz rating so at a QCW frequency of 350 to 500KHz are they suitable because of the low QCW duty cycle?
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
They are indeed MICA you can tell just by how heavy they are. A film cap would work but you wold need to make a MMC of it in order to get a suitable RMS rating. That MICA cap is an excellent QCW capacitor, as they will handle the high RMS ratings of a the QCW wich can be near CW. I bet a doorknob cap would work as well although you may need to make a MMC out it.
The caps in Dr. Spark's picture have a 100KHz rating so at a QCW frequency of 350 to 500KHz are they suitable because of the low QCW duty cycle?
Just because the IGBTs 60N60s are rated at 60A that didn't stop anyone from running them at 600A pulsed.... Ratings are made to be broken
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi teravolt,
Sorry to disappoint, but those all look like KVI-3 caps. I got fooled the same way - they're pretty useless for any useful reactive power handling. They are actually the same material and purpose as those blue drop HV ceramic caps, just in a fancier packaging...
I've found that general rule for russian caps is, if they don't have KVAR rating written on them, they aren't intended for it at all!
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Dr. Spark wrote ...
Have had good luck with Strontium Titanate doorknob capacitors as abused them in the dual 833c VTTC and they never got hot @ , only issue is they are mucho $$$$$$. Have lots of flavors of doorknobs, some work well for RF and others get hot and are more designed for bypass caps. Issue is if they get hot, the value changes detuning your tank.
Have been collecting Mica’s as a hobby as they are getting harder to find and the prices are getting silly. They are very heavy caps but worth the weight indeed. Seeing the Sangamd caps used for over $250 each…that is just crazy. Guess Mica’s are a good investment hee hee.
Rgs, Dr. Spark
I would much rather invest in MICA's then stocks right now Can I get the name of your MICA broker Dr. Spark?
Registered Member #1034
Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154
Teravolt, The Russian caps may not be the best but they work ok for me. Anything works better than vine bottle capacitors although I do miss the smell of ozone produced by the corona around the tops of the bottles.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
thanks for the encuragement RogerInOhio, I plan to use them in a pulsed duty application and I will derate them and see where it goes. I think they will do something. I have plenty of mica's to do what I want if they don't work
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QCW coil
