[TenTec] PA current control

[Dr. Gerald N. Johnson]

On Sun, 2007-09-23 at 22:36 -0500, Bob McGraw - K4TAX wrote:
> The control of PA current is derived from a R in the A+ line to the PA.  The
> voltage across the R is fed to the 2nd mixer board and driver which reduces
> drive inverse to the PA current.  The current never gets to max
> destruction value.
> 
> Having a Paragon manual in front of me, the current sensing R is R1 {0.015
> ohm 10W} located on the DC power board.  This voltage is fed to U2a which is
> a level shifter and its output  feeds U2b to which the output if it exceeds
> the Ic limit of 22 amps at full power, diode D25 is forward biased and ALC
> actions results, therefore reducing drive to the PA stage.  Thus PA current
> will always be limited to a max of 22 amps for some 300 watts input
> regardless of load Z.  Yes, in theory, it will drive a dead short with rated
> output.  Remember the Tentec PA is not current limited.  It is drive 
> limited.
> 
> The fuse, the circuit breaker and power supply limiting serve no purpose 
> except
> in the event of catastrophic failure and thus exists simply for the 
> protection of
> other components.
> 
> Big difference.
> 
> 73
> Bob, K4TAX

I can't find my Corsair II manual at the moment, but I've not observed
that collector current reduction in my Corsair II. Given a bad load Z it
simple blows my fuse protector.

73, Jerry, K0CQ