[Amps] SB-220 bias question

[Joe Subich, W4TV]

> That was not the original question. The gentleman asked if he 
> tuned up at 1500 watts output and then reduced the drive so 
> the output was now 800 watts, would that harm anything? You 
> answered yes it would cause harm and you were mistaken. It 
> won't. Retuning was not part of his question. 

If you don't retune the output network when operating in a 
continuous power mode (CW or RTTY) at a lower power level, 
the loading will be incorrect.  Linearity may or may not 
suffer, efficiency will certainly suffer, and since the 
loading is incorrect it will be difficult without doing 
the math or taking measurements in an intentionally miss- 
tuned amplifier what the voltages/currents in the tank 
are.  

One thing is certain, improper loading has caused more 
damage to amplifiers than any other cause.  Intentionally 
mistuning an amplifier is, to quote the President, "stupid."
  



> -----Original Message-----
> From: Bill, W6WRT [mailto:dezrat1242 at yahoo.com] 
> Sent: Sunday, August 30, 2009 9:44 PM
> To: lists at subich.com
> Subject: Re: [Amps] SB-220 bias question
> 
> 
> ORIGINAL MESSAGE:
> 
> On Sun, 30 Aug 2009 13:49:00 -0400, "Joe Subich, W4TV" 
> <lists at subich.com> wrote:
> 
> > You can
> >not operate a network designed for one plate load impedance 
> >and twice the impedance without returning (sic).  Once you 
> return, (sic) 
> >the network is different - the Q is different and the currents 
> >are different. 
> 
> REPLY:
> 
> That was not the original question. The gentleman asked if he 
> tuned up at 1500 watts output and then reduced the drive so 
> the output was now 800 watts, would that harm anything? You 
> answered yes it would cause harm and you were mistaken. It 
> won't. Retuning was not part of his question. 
> 
> All the other stuff you have been quoting is nice but is NOT 
> related to the gentleman's question. 
> 
> Please do what I suggested - perform the action above on a 
> real amp and see if you can find where any component has any 
> increased stress whatsoever. Report back with enough detail 
> so everyone can understand your procedure and  duplicate your 
> setup. I can't wait to hear the results. 
> 
> 73, Bill W6WRT