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Re:Re: Caps Question:
I believe all ceramic "door knobs" are "DC" rated. I have used 30 KV 4000
pF ones in service with 15 KV 120 neon and with a Vac tube coil, they do
work, but are quite loosy at RF frequencys. They tend to heat up and drop
in value, which can affect tuning.
Yeh, MMC's are great.
On Wed, 6 Sep 2000, Tesla list wrote:
> Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
> Hi All,
> I was involved in the development of MMCs so all my research effort went
> into that direction. The doorknobs caps are still alive and well. I still
> use MMCs since they are so easy to adjust and I now have a number of coils
> that require tight value caps.
> I run all my caps really hard in an effort to prove out MMC designs. I go
> over voltage and over current as standard practice. However, it is easy to
> conservatively design them too. Much information is at:
> I can't say too much or your doorknobs. If they are unmarked, they could
> be anything... All I can suggest is to try them and see if they blow up
> which is not a great option...
> At 10:24 AM 9/6/00 -0400, you wrote:
> >Thanks Terry! It sounds as if you have tried the doorknob caps and
> >traded them in so to speak for the mmc's. What would be your principle
> >reason for using the mmc's? Better spark? More Spark? Why did you stop
> >using the doorknobs? It sounds like you are on to something that I have
> >yet to get a grasp on, even with my previously bad experience with the
> >mmc's. Maybe I used the wrong types of caps and expected too much from
> >them. Will your mmc's take a sustained run? There is not much more time
> >to Halloween, and I need something good for a new fourth coil I am
> >building. I need two good coils running simultaneously and cannot find
> >any more 'good,cheap' doorknobs to fit my budget. I would need a minimum
> >of 30 more ganged in series for my 4th coil. That is why I wonder if I
> >could use my existing 40kv doorknobs singly, so I could split up my
> >supply of them. They are 'new' caps and cost $25 each. I have 30 of
> >them. Do you think that maybe that is why they cost so little and have
> >no coherent A.C./D.C. markings? Possibly seconds or fallouts? They
> >do work very well in series, but I am scared to try them singly unless I
> >can somehow find if they are 40kv A.C. rated. Although I may never
> >really know. Al
> >On Tue, 05 Sep 2000 17:49:30 -0600 "Tesla list" <tesla-at-pupman-dot-com>
> >> Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
> >> At 03:09 AM 9/6/00 -0400, you wrote:
> >> >Hi Terry! Is this the proper way to get into the website when I
> >> have a ?
> >> >about coiling? If not please tell me how and I will rewrite this
> >> >mailing.
> >> Yep, this is it!
> >> >If it is correct, then, is there anyone on the list that could
> >> >tell me if my doorknob caps would be rated for A.C or D.C. if there
> >> is no
> >> >mention of it on the cap? The people I got them from did not know
> >> the
> >> >voltage type. They are .004mf at 40kv. So, is there any unwritten
> >> rule
> >> >that will tell one what type of volts the device is rated for when
> >> there
> >> >is no info on the cap? Reason I am asking is because I would like
> >> to use
> >> >the 40kv caps as singles on my coil rather than doubling them up in
> >> >series the way I have them now, but I don't want to fry them by
> >> learning
> >> >the hard way that I did when I used a gang of hockey pucks which
> >> were
> >> >15kv rated and stamped as D.C. volts on the shell. It gets very
> >> >expensive in a hurry when these caps fail.
> >> If they are new, you can tell be the price. AC high Q door knobs
> >> are
> >> really expensive. Like $100+ each... It is odd they are not marked
> >> I
> >> have a bunch of 30KV 1.72nF TDK caps that are about 1.5 inches in
> >> diameter
> >> and 3/4+ inch thick. If they look of very high quality and have
> >> heave
> >> terminals they may indeed be nice high-Q types. If anything on them
> >> looks
> >> like rolled paper, they are definitely low-Q.
> >> >I had the 15kv D.C. caps
> >> >doubled up in series for a 30kv D.C. rating on my two 15kv -at- 60ma.
> >> neons
> >> >and the caps still fried fairly quickly. So should I just leave
> >> the good
> >> >40kv caps doubled up as I have them now just to play it safe,
> >> because
> >> >they appear to be indestructible when doubled. Has anyone else had
> >> >experience with this kind of setup? I know that M.M.C. cap banks
> >> seem
> >> >to be the rage, but my luck with them was no good when I used them
> >> for a
> >> >sustained 15 minute run. Have any of you coilers had better luck
> >> than me
> >> >with M.M.C. caps on extremely long runs? Because those little
> >> M.M.C.
> >> >scutters get real expensive too when the banks fry. I have never
> >> had
> >> >just one go bad, nosiree, they would short or open up in grand
> >> fashion
> >> >and drove me nuts troubleshooting the banks looking for the
> >> culprits. I
> >> >would like to try the M.M.C.'s again but would like to hear from
> >> others
> >> >first. Is there a really prime M.M.C. cap available that would go
> >> for
> >> >say, at least possibly more than an hour with no damage that I
> >> could use
> >> >on my yet to be built fourth coil? Thank you, Al.
> >> MMCs will easily work but you have to use polypropylene pulse rated
> >> caps
> >> and only run about 3 amps RMS through each string. If they get
> >> fairly
> >> warm, the current through them is too high and they will melt
> >> internally.
> >> If you try MMCs again we can help with the details.
> >> >
> >> >So many questions! So little time!
> >> >
> >> Cheers,
> >> Terry