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Re: Dump the RSG
From: Robert W. Stephens[SMTP:rwstephens-at-headwaters-dot-com]
Reply To: rwstephens-at-headwaters-dot-com
Sent: Sunday, November 09, 1997 8:01 PM
To: tesla-at-poodle.pupman-dot-com
Subject: Dump the RSG
All,
As a further note to my last post about increasing the pulse power of
a given triode employed as a power oscillator while maintaining
manufacturer's specified average power by gating it to shorter duty
cycles I forgot to mention that this works until you overvoltage the
tube to the point of sparking internally, or exceed the electron
sourcing ability of the cathode structure, this latter limitation
being the subject of previous list discussion.
I have picked up a pair of rather unique vacuum triodes known by the
part number JAN-6544. These look like external anode, forced air
cooled transmitting triodes of the ~5 kW plate dissipation class except they
have a much more humongous cathode structure. They are specifically designed
to pulse modulate HVDC to magnetrons and the like and can deliver 1 MW
of continously repeating pulse energy at 20 kV.
Specs courtesy Richardson Electronics on their own National NL-6544
follow.
Absolute maximum ratings:
DC plate volts...................................20 kV
Peak plate volts.................................25 kV
DC grid voltage.................................. -600 volts
Peak positive grid voltage.................. +1500 volts
Peak negative grid voltage.................. -1500 volts
Pulse cathode current......................... 75 amps
DC plate current................................ 250 mA (? rwstephens)
Grid dissipation................................. 75 watts
Plate dissipation................................ 1 kW
Pulse duration.................................... 6 uSec
Duty factor........................................ 0.03 %
Typical operation:
DC plate voltage................................ 18 kV
DC grid voltage.................................. -250 volts
Pulse positive grid voltage................. +1200 volts
Pulse plate current............................. 65 amp
Pulse grid current.............................. 7 amp
Pulse driving power.......................... 12 kW
Pulse power output.......................... 1.0 Mw
Pulse output voltage......................... 15.5 kV
Duty factor....................................... 0.003 %
Some general characteristics:
Filament voltage................................ 6.0 volts
Filament current................................ 60 amps
Fil starting current............................. 300 amps
Cath. warm-up time.......................... 10 minutes
Amplification factor.......................... 90
Spec sheet description:
"The NL-6544 is a shielded-grid triode designed primarily for use as a
switch tube in hard-tube pulse modulators for radar applications. It
delivers a peak pulse power output of one megawatt with less than
10 kW of driving power. The tube incorporates a beamed electrode
structure to minimize driving power. This design avoids the
fine-wire grids usually used in tetrodes and provides a rugged
structure. The shield grid is strapped to the cathode internally and
protects the cathode from transient arcs. These features provide a
tube which operates much more stably at high voltages than hard-tube
modulators of earlier designs. The high amplification factor
combined with low grid currents results in unusually low driving power
requirements. Additionally, the the input and output circuits are
isolated so that their feedback capacitance is small. The cathode is
a unipotential oxide-coated type. The anode is force-air cooled and
is capable of dissipating 1 kW with an air flow of 80 cfm."
I should think that a small hydrogen thyratron employed as a pulser
ala radar modulators could be efficatiously employed to provide the
modest 10 kW pulse power required to drive the grid of this switch tube from
a low power control signal circuit.
I submit this information to this open forum fully cognisant of the
fact that it will only add to the state of confusion as to what
choices we have, as Tesla coilers, to gap alternatives. It appears that a
medium sized maggy could be operated from a pair of these tubes in
parallel (Richard Hull?!). It (still) will be interesting to see if anyone
out there amongst you sleepyheads comes up with any working models of
anything other than a relatively straightforward spark gap,
stationary, series chained, blown and/or sucked on, or mechanically whirled.
John Freau has reported some interesting work pulsing vac tube TC's
in novel ways. Others are coming on-stream in vac-tube TC
experimentation. Good luck all!
rwstephens