[TenTec] century 22 setup driver and pa

[Bwana Bob]

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
>