Re: Tube coil makes sparks

At 04:18 PM 3/9/1999 , you wrote:
>Original Poster: Brandywine <brandywine-at-writeme-dot-com> 
>Fellow Coilers,
>   There has been some debate over the usefulness of the MMC capacitor
>arrangement. I am currently using 6-- 0.018 uF, 1600Vdc, Panasonic
>metallized polyprop caps in series for the tank capacitor (result =
>0.003 uF). They were  mildly warm after a 5 minute run at 4000 Vac and
>probably 4+ kW.  I was hoping they would run stone cold. A permanent
>setup could incorporate 24 caps in a series parallel arrangement, for
>example. Despite the modest heating, I must tentatively conclude that
>they are satisfactory for high power tube coil duty.

Glad to here that you have had first light with this coil. I have been
using the Panasonic caps also, I am using 10 of the 0.015 uFd-at-1.6KV in
series wired so I can tap the last 4. They do perform well in my opinion,
but they get warm after several minutes, although, even after the heating,
they do not loose capacitance value, as do the doorknob variety.  I must
add that they are of great quallity, as mine have all measured within 2% of
their rated value.

>   I have in my possession a total of 4-- 833As. It turns out that one
>of these produces a beautiful blue glow consistent with John F's
>description of a current sucking corpse that is distinctly unusable. Of
>the 3 tubes remaining, 2 have graphite plates. To say that they are more
>stout than those with conventional plates is an understatement---where
>the conventional plates are bright orange, the graphites are barely
>glowing. I may need to bias the tubes separately.

Sorry to here about that tube. Yes! Those Graphite variety are real beasts!
I have just tried my three in parallel (2 graphite 1 sheet metal), and the
poor sheet metal one gets very bright, while the Graphite ones show no
color at all on the plates. 

>   I'm using a 100 watt, 10K variable Ohmite resistor for grid-bias
>duty. $ 25.00 from Digikey. I almost bought the 225 watt version. Wish I
>had. The 100 watters can get quite hot, especially when  less than half
>of their resistance is utilized. In retrospect, it may have been better
>to obtain several fixed value units so that the full heat dissipation
>capacity of the single resistor may be mobilized.

I have to agree, I use several in series (100 and 200 watt) and they still
get hot. 


David Trimmell

>  So there is my report. Much work to do. The cancerous desire for more
>power was felt very early on. I know that 3 tubes will produce much more
>than 20" sparks, but a gentlemen at Elex electronic supplier mentioned
>the availability of 10,000 watt industrial oscillator tubes. ...
>Dave Hartwick