Both of the topics I see discussed here are things I had to deal with
also in the past few years. The type N connectors kept blowing up at
4 kW peak RF, 200 MHz, when VSWR crept up during tuning. THis is
about 900 Watts of average power. This was in the interstage
connection from Driver to IPA, and the driver was an old RCA cavity
amplifier with 7651 tetrode in it.
We switched the 7/16 DIN connector, as it had superb specs, and never
have had another problem. At 200 MHz, type LC, C or UHF (PL-259)
would not be best choice.
Another thing I have seen is the use of UHF connectors by some HV
power supply companies such as Universal Voltronics. They remove the
phenolic or PTFE insulator from the chassis mount female, and recess
the center pin back inside the chassis. The male cable plug is a VERY
modified UHF, only using the outer shield ring, and with a special
center plug. Looks real cheap but works.
-----------------
We use some common spark plugs (no i don't know or really care if
they are antifouling as long as they ionize and fire) as protectors
for the screen to cathode of 4CW250,000Bs. I have two on each tube,
and I purposely file off the bridging wire (ground side of gap) to
make the voltage more predictable and repeatable. With it, they
breakdown fairly easily, at a few kV. With the wire gone, they seem
to fire at 4 kV or more. This is easily verified with the hipotter,
and at our altitude (7000 feet above sea) it is important to test
every one first. I pulse that screen grid at up to 2500 Volts, so I
need some margin here.
We also use them in large power supplies between the negative lead of
the capacitors and the chassis (in this case, the wall of the room).
When there is a crowbar or arc on the B+ lead, the negative jumps,
and it is held within a few kV of ground via sparkplugs, as well as
some husky Harris (now Intersil?) MOVs.
We inspect these once a year, and usually replace a few which are
burnt up. They're cheap enough and so easy to purchase at Pep Boys.
For lightning protection, i would imagine that spark plugs get
'fouled' pretty badly from a direct hit. I would also imagine that
they would go flying across the room like a projectile. BUT, they are
probably very good to prevent damage from nearby hits, where the
induced voltage on an antenna is enough to make a healthy jolt to
your rig.
73 and Happy Thanksgiving,
John
K5PRO
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