I am very close to making a swept frequency measurement of a large Pi
network, for a tetrode amplifier. The two vacuum variables are mounted
vertically, by coincidence, because it makes for short path for ground
(lower L) and our mechanical layout of the tuning shafts are underneath the
power amp deck, below tube socket. Using flexible shafts for part of it.
I measured an old 50 Ohm Carborundum style resistor last night. Sometimes
they are called Globars. It is similar to those made by Cesiwid now. It is
an 885 AS style, is 0.75 inches in diameter, and 2.5 inches long. The power
rating of this part is 15 watts average, with 2500 Joule peak energy dumped
in it, or 4 KV peak across it.
Dc resistance was about 52 Ohms or so. Using the Hp 4815A vector impedance
meter, i cranked it from 1 to 108 MHz. The magnitude stayed slightly over
50 Ohms, and the phase angle only began to slip positive, about 2-4 degrees
from zero, at 108 MHz. That says that this particular R is pretty damn good
for a "non-inductive" power resistor, and might work nicely in a particular
damping or suppressor application. Sometime when I have one handy, I'd like
to measure one of the bigger pieces.
John
K5PRO
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|