Re: [TCML] Tube question

["Phillip Slawinski" <pslawinski@xxxxxxxxx>]

David,

I run 10K on my 833C coil.  It's working quite well now that I've worked out
most of the bugs.  I'm getting about 21" in continuous mode without a
grounded target.

On Sun, Sep 21, 2008 at 5:04 PM, David Rieben <drieben@xxxxxxxxxxx> wrote:

> Ed,
>
> I've also discussed my situation with Cameron Prince and he feels that my
> problem is likely with the grid resistance. I am
> using a appr. 100 watt rated 0 - 25 K ceramic wire wound
> resistor that I have set at 10 K. However, I epoxied the resistor
> down to the base and the epoxy has also glued down the "ring"
> of the slide tap so I would almost certainly destroy the resistor by trying
> to unglue it and vary the tap. Cameron stated that he
> had to bring down the 10 K closer to 8 K to get his 833(C) to
> work correctly with his coil after replacing the 833(A). So it
> looks like I may have to opt for a high wattage variable rheostat
> with a 0 -20 K resistance rating, or something like that.
>
> David
>
> ----- Original Message ----- From: "Ed Phillips" <evp@xxxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Sunday, September 21, 2008 12:56 PM
> Subject: Re: [TCML] Tube question
>
>
>
>
>>
>> David Rieben wrote:
>>
>>  Ed,
>>>
>>> I am not currently metering the grid (or plate) current
>>> in my setup, so I cannot answer the current question. I am really pretty
>>> dumb on vacuum tube coils and this one
>>> was based loosely on Steve Ward's 833A VTTC that
>>> is supposed to yield 22" sparks in stacatto mode. The
>>> only difference is that I am using 2 seriesed MOTs
>>> through the voltage doubler circuit, just like Cameron
>>> Prince did on his. As a matter of fact it was my perso-
>>> nal viewing of Cameron's coil's output that convinced me to take on this
>>> as my first VTTC project. Anyway,
>>> I have used two or three different used 833As and always
>>> got about the same output. However, I decided to or-
>>> der a new (Taylor) 833C because Cameron had pur-
>>> chased a used one on eBay and had reported good
>>> results, mainly the plate stays cooler at a given power
>>> level. However, when I tried my new 833C tube in   my circuit, it had a
>>> very limited spark length output and the spark output would not increase
>>> beyond about 40%
>>> on the variac knob but would instead start to take on
>>> a "crackly" sound. BTW, the output at this point is only
>>> about a pitiful 6 to 8", in continuous mode! Further ramp-
>>> ing up of the variac beyond this point does not increase the
>>> spark length any further but it is apparent that there is more
>>> plate current as the graphite plate will begin to take on a
>>> glow. BTW, the output sparks will continue to grow pretty
>>> well linearly with increase in the input via twisting up the
>>> variac knob when using the old 833A until I can't really turn it up much
>>> past 60% on the variac knob due to ex-
>>> cessive plate glow (in continous mode), but the spark length at this
>>> point is around 16 to 20".  Any more suggestions, I'm all ears :^)
>>>
>>> --
>>> David Rieben
>>>
>>>  David:
>>
>>   Without current measurements I don't really know what to tell you -
>> there simply isn't enough information.  Do you have meters so that you can
>> do that?   I would suggest boosting the filament voltage and see if that
>> makes a difference.  The fact that the output doesn't go up after a certain
>> plate voltage is suggestive of limited emission and going from 10 volts to
>> 11 volts should make a significant difference and certainly won't damage the
>> tube in the short run [few minutes of operation].  You didn't tell me what
>> value of grid resistor you are using but it's possible cutting it in half
>> for a test might also increase the output.
>>
>>   The increase in "plate glow" [hope it's a very dull red at most] with
>> plate voltage doesn't necessarily imply an increase in plate current as the
>> voltage increase alone will increase the power loss in the tube,
>> particularly as you don't get more output.  The plate input power goes
>> either into the load [streamers] or is lost in the tube.
>>
>> Ed
>>
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