connex 4300hp bias setting

[troyota]

hello,
i just replaced the final in this rig. i was looking for the info on setting the driver and finals bias. anyone know the procedure, and voltage?
thanks and happy new year


oops...i forgot to say i put a 2sc2879 in, because i had no 2sc2290, thanks

 

[9C1Driver]

That's probably not good, that radio was set up to handle a 2290. cbtricks.com probably has the alignment procedures. I would get with a tech on the forum that's willing to talk with you and see what else has to be changed/swapped/upgraded to match up to that larger final. Those radio's were always touchy, i'm sure with a 2879 it will be downright cranky and run even hotter.

 

[mackmobile43]

7 mA on the drive, don't think it has final bias but that's with the 2sc2290 final.

There are heat sink limitations to that radio and a 2879 produces a bit more heat.

 

[troyota]

thanks for the replies,
the 2290 dissipates 175 watts of heat and the 2879 dissipates 225 watts of heat according to the datasheets. that is if i read it correct. i was not going to run it full out. maybe 60-70 percent. depends on how it acts.
i see vr11 in the corner of the board next to the 2166 driver. i assume that is the bias vr for the driver.
is there a certain procedure? like band, mode, and channel to set it to before adjustments? to get my 7ma where do i hook my meter? i have a dvm, with current readings too.
thanks

 

[mackmobile43]

thanks for the replies,
the 2290 dissipates 175 watts of heat and the 2879 dissipates 225 watts of heat according to the datasheets. that is if i read it correct. i was not going to run it full out. maybe 60-70 percent. depends on how it acts.
i see vr11 in the corner of the board next to the 2166 driver. i assume that is the bias vr for the driver.
is there a certain procedure? like band, mode, and channel to set it to before adjustments? to get my 7ma where do i hook my meter? i have a dvm, with current readings too.
thanks

Not sure about most of that but measure the voltage on the base leg of the drive stage transistor.

 

[troyota]

i was working on a 2510 president a while back. the driver is a 2sc2166, just like this one. the bias setting on it was 50ma. why would the cutoff be different in this radio with the same transistor? different circuit? because of the 2290 final? i thought the 50ma was to cut it off, mabey they dont work like a tube cutoff. not doubting you, just askin.....
thanks again

 

[mackmobile43]

i was working on a 2510 president a while back. the driver is a 2sc2166, just like this one. the bias setting on it was 50ma. why would the cutoff be different in this radio with the same transistor? different circuit? because of the 2290 final? i thought the 50ma was to cut it off, mabey they dont work like a tube cutoff. not doubting you, just askin.....
thanks again

Bias voltage is there to keep the transistor turned on between audio peaks to eliminate distortion so if it turns off then there must be a clamping circuit involved.

If you're referring to idle current it should be constant, that's what the regulator circuit does , 5 volts and is most likely what a mosfet runs at but the 7mA being just over 1/2 volt is close to class ab.

Not sure if you rig has constant voltage on the transistor or is switched on at time of tx(what I prefer) but it should remain constant during tx.