Carlos:
To read the current, you can unsolder the red +12 V lead to the driver
and final board and insert a milliammeter in series with it. This will
give you total current into the board. I don't know if the 30 mA and
140 mA settings refer to total current or collector current, so this
would affect the procedure, which I don't have. If it's total current,
you set the current into the board to 30 mA, then go key down with no
drive and set the current to 140 mA. If the values represent collector
current, you will have to set the driver bias to min, read the current
into the board and adjust the driver bias for an increase of 30 mA, then
go key down and adjust the final bias to increase the current by 140
mA. I'm looking at the manual for my Corsair, which used the same
driver transistors (MRF-475) as the Century 22. The Corsair manual says
to set the driver bias to 4 to 8 mA, so the 30 mA must refer to total
current into the board. After I replaced my C-22 finals, the total
current into the board was 159 mA, which I reset to 140 mA TOTAL.
I wasn't sure about this procedure, so last week I contacted the factory
by e-mail, asking how to set the biases and Paul Clinton replied and
said that I should set the base voltage on the drivers to 0.07 volts,
then with the drive at zero, lock the radio into transmit and set the
final bias voltage to 0.07 volts. There is a test point pin next to the
base of each transistor. Here is the text of his e-mail:
"With the 579 in receive mode set the base voltage of the driver
transistors 0.07 volts DC using a digital voltmeter. Place the 579 in
LOCK with no drive and adjust the base voltage of the final transistors
to 0.07 volts DC."
This is a very much different procedure. My guess is that the C-22
driver and final were originally set up for class AB linear operation
and Ten-Tec later changed it to class C, since CW transmitters can run
OK in class C. Maybe someone else has some insight into this. I haven't
tried the 0.07 volt settings yet. My C22 is presently on the bench with
a possible intermittent short that causes excessive current drain in the
final. I'm still working on it, but will let you know when I get it
back on test.
By the way, Ten-Tec replaced the original drivers and finals with type
2SC1969.
73,
Bob WB2VUF
On 1/28/2011 4:08 PM, carlos popelier wrote:
hello,
current settings for driver and pa by tentec are 30 mA and 140 mA,
this is done by setup driver and pa potentiometers,
question: how can i measure this current values and the best way to do it,
or the entire setup procedure.
thanks carlos
|