Here the air cooled 50 ohm, 1100 watt glitch resistor assy is installed.
Consists of 4 x 50 ohm, type SP globars.....wired in series - parallel.
These are the glass bodied types, designed for oil immersion.... made for
dummy loads. For this application, air cooling is ample. The cooling air
is from the intake (filtered) air that feeds the intake of the EBM-Papst
330 cfm @ .9" blower. The open space in the middle of the chassis is
where the blower will hang down from the RF deck above this power supply.
(both in the same cabinet). The air being sucked into the blower 1st has
to pass by the entire power supply assy as seen here, including the 50 ohm
glitch assy.
Each resistor is 1" diameter x 12" long. Ceramic standoffs used plus
1/4" thick Teflon mounting plates.
In normal operation, with a 2.5 amp DC plate current load, for CCS data
modes, total diss in the glitch assy is 312.5 watts or 78.125 watts per
resistor. Using processed SSB, average plate current is just 1.25 amps,
and total glitch assy dissipation is 78.125 watts or just 19.53 watts per
resistor.
Each resistor is rated for 275 watts CCS in free air, BUT this is at a very
high temp, 350 deg C (662 deg F).
Each resistor is rated for 3200 joules / 10 kv... or 12,800 joules in
total. Energy stored in the 20 x 2500uf lytics is 3515 joules. This is
with 7.5 kv no load. 1 joule = 1 watt second.
The filtered B+ is 1st fed to the BUSS HVU-3 HV fuse..... then to the 50
ohm glitch assy.....then off to the RF deck. With any B+ to chassis /
grnd arc, or say an anode to grid arc, the fault current is 7500v / 50 ohms
= 150 amps. 150 amps will open off the 3 amp rated HVU-3 fuse in 1
msec (tested). The 50 ohm glitch assy LIMITS the fault current to a safe
value.... while the HV fuse INTERRUPTS the fault current....... event over.
https://www.youtube.com/watch?v=unvJ3oV2kBw&t=349s
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