[Amps] SB-220 bias question

[Joe Subich, W4TV]

> Fine, but none of those amps change the plate voltage in the 
> different modes, so you mean to tell me they are designed wrong?

No, I'm saying they are all designed to operate at 1500 Watts 
output.  If one reduces power without reducing the plate voltage 
appropriately, the plate load impedance will change.  Unless the 
"L" in the pi-network is changed to the correct value for the new 
plate load impedance, the pi network will be very different than 
what was designed for normal operation. 

If the components (particularly the pi-network coil and band 
switch) are not sized appropriately for the higher currents 
and voltages, they will fail prematurely. 
  



> -----Original Message-----
> From: Gudguyham at aol.com [mailto:Gudguyham at aol.com] 
> Sent: Saturday, August 29, 2009 8:57 PM
> To: lists at subich.com; sub1 at rogerhalstead.com
> Cc: amps at contesting.com
> Subject: Re: [Amps] SB-220 bias question
> 
> 
> 
> 
> In a message dated 8/29/2009 5:49:01 P.M. Pacific Daylight 
> Time, lists at subich.com writes:
> > but the AAL-80, AL-82 et al. do not change the plate
>   > voltage on any mode.  The operator is told to adjust 
>   > power output according to the mode.  
> 
> Reducing the power output without changing the plate voltage 
> will result in a miss-tuned condition.  If the pi-network is 
> tuned for full output and the drive reduced (power adjusted). 
> If the output is retuned and the lower drive level, the plate 
> load impedance will be incorrect for the design of the pi- 
> network and the pi-network will need to be detuned (run at 
> a higher Q).   
> 
> Fine, but none of those amps change the plate voltage in the 
> different modes, so you mean to tell me they are designed wrong?
> 
>  
>