VTTC provisional results

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Herwig Roscher by way of Terry Fritz <twftesla-at-uswest-dot-net>" <herwig.roscher-at-gmx.de>


Hi all,

After having finished a series of tests I would like to inform you of 
the results and , of course  :-)  , I have a few questions as well.

My system:

primary coil:
diameter    : 8"
inductivity : 640 µH
capacity    : 700 pF
turns       : 67
coupling    : primary 1.2" above secondary

secondary coil:
diameter    : 4"
inductivity : 35 mH
turns       : 1370

toroid/corona shield 1.2" x 6", 1.2" above the secondary coil, 
discharge pin

grid coil:
diameter    : 8"
turns       : 8
coupling    : grid coil 1.4" below primary coil
grid leak R : 15 kOhm
grid leak C : 3.75 nF

The oscillator frequency  is about 200 kHz.
I am using a 4PR1000A tetrode, driven from a 10 kVdc (filtered) 
power supply.

Output (the most important thing of course):
I am getting a bunch of branched streamers which are 
accompanied half of their length by thick blue seams. Occational 
thick arcs to a grounded rod at a distance of 17". Should I be 
satisfied?

Measured full load values:
Plate voltage       : 8500 Vdc
Plate current       : 375 mA
Screen grid voltage : 1280 Vdc
Screen grid current : 140 mA
Control grid voltage: 200 V
Control grid current: 20 mA

Unfortunately (some of) these values are probably wrong, as I could 
not find a really "cold" reference point within the system. The tube 
oscillates in C-mode and there are spikes all around, 
superimposing the values to be measured. The only point 
connected to the rf-ground is the base of the secondary coil. All 
other "grounds" are connected to the ground of the house wire 
system. I have connected both grounds of course but could not see 
any difference.

Unfortunately there was another flashover between the primary and 
the secondary coil: From the flush screw (correct expression?) I 
am using to fix the upper end of the primary winding there was a 
thick carbon track (more than 0.1" wide and deep) to the upper end 
of the coil form. From here the spark jumped to the 6" protection 
tube I have placed between the coils and furtheron (without 
puncturing this tube!) to the secondary coil. It hit it at the same 
place(!) as it did before(one time). I am suspecting that this is not 
an accident. Any hints to prevent my secondary from being hit any 
more?

As tetrodes require high plate resistances I would like to increase 
the number of the primary turns even more. But there are some 
drawbacks:
- More turns means a higher coil (if the wire diameter was not 
changed) and a greater menace of flashovers - see above.
- More turns means a smaller tank capacity and a higher influence 
of the ambient capacities and capacity-changes. Has anybody 
used tank capacities smaller than 700 pF?
- More turns means a lower turns ratio primary/secondary and a 
lower secondary peak voltage therefore. This could be contrary to 
an improvement of the output. Is this correct?

Critics and hints are very appreciated.

Herwig