[TenTec] Omni C PA bias
k4mt1950 at charter.net
Fri Dec 13 20:29:35 EST 2019
I am working on an Omni C for a new ham and it has PA bias issues.
I can see and adjust thr\e driver bias but PA bias adj on the bias/OT
board does nothing. I measure .7 volts on the
bases of the PA transistors but see no current other than driver bias.
There is a regulator IC and pass transistor on regulator board. I only
see .7 volts on the bias pin to the PA and I guess since bias is feeding
right into base/emitter junction that might be normal. If I unhook PA
from bias board i read over 7 volts output but once I connect the bias
comp diode it drops below 1 volt. And drops again when I hook bias to
PA devices down to .7 volts which I can adjust with the bias control.
The PA devices check OK with ohm meter and all the junctions are there.
What am I missing? Is the regulator for the PA bias not functioning
correctly? Are the PA devices shot and have no gain?
I have worked on these in the past but its been too long to remember
what is normal.
I have not tried putting drive to PA to see if it outputs power.
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