Carborundum resistors were also common in tube FM broadcast transmitters
down to 1 kW level for the same application. Dale or Ohmite (or Ward
Leonard!) 25 watt wirewound resistors don't hold off voltage well across
4 kVDC, when there is a low impedance breakdown to ground at the RF
circuit/tube. If one is lucky, they blow open like a fuse, as mentioned
by others. If not, they allow the load arc to take out a bit more metal
than Eitel and McCullough can tolerate. It's an insurance policy, not
needless over-expense, by my estimation.
Big amp here running today at 325 kW avg. Don't use globars for series
limiters at that level, use active crowbar devices with very small
resistance to keep the crowbar alive when clamped.
73
John
K5PRO
On 4/17/13 4:19 PM, Carl wrote:
Ameritron/MFJ sells a Globar they use for a glitch in their "senior"
amps. Overpriced and uneeded IMO at those power levels. A plasma isnt
going to even get started before the fuse blows anyway...this aint a
250KW application!
Carl
KM1H
-
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|