rf - Free and Open Source Software

4 x 150 Sockets
Larry Jack, WA3AQS
7421 Gwynndale Drive
Clinton. Maryland 20735
It was abo ut a week after completing the
small sideband rig that I realized its single
watt wasn't going to be enough. After a
few, "You're readable, but kind'a weak" signal
reports, I returned to the junk box, this
time for parts to build a linear. From a­
mong the assorted trivia were unearthed a
handful of 4x ISO's. Two hundred watts
output at least -va very good tube for the new
amplifier- but I didn't have any sockets for
the m. Being a little impatient to get started,
an d ad vent urous at heart, I elected to
build the sockets rat her than wait out an order
fro m a supply house.
A simple modification of a regular octal
socket provided a new base. A ceramic type
(for its low losses) was selected. Then all the
metal pins were carefully removed from the
collar. The pins are crimped to make firm
connections with the new size pins of the
4x 150, and then are replaced back into the
socket.
SCREEN AIN G
FIGURE 2
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FIGUAE 1
A grid connector was made by flaring the
top of a semi-circle of sheet metal about 1 Yz
inches high (Fig. JJ. This connector was
placed into the socket key so that the gap
between the semi-circle lines u p with the
slot in th e key of the base. To prevent the
co nnector from slip ping out again, solde r
was melted about it, on the underside of t he
new tube base (Fig. 2). For cooling, the
tubes were placed almost directly in the
mouth of a large squirrel cage blower.
I originally had used only a single .0 I IlF
capacitor soldered directly at the socket pin
as the screen by-pass. The rig took off, so
to speak, in a very unstable fashion , so small
straps on a standoff insulator wit h another
.01 IlF capacitor was put above the chassis
to by-pass t he tu be's screen ring. This cured
the troub le (Fig. 2).
Cooling never fig ured as a problem. At
50 MHz with inputs reaching 600 watts, a
120
FIGUAE J
single 200 cfm blower has kept a pair of onefifties
running cucumber cool. Not so many
"kind'a weak" reports now.
.. .II'A3AQS
,
73 MAGAZINE