[TenTec] Tuning Amp on 17 meters

[Richards]

On 4/17/2013 5:06 PM, Jim Brown wrote:


> Measured how? By the rig, or by the amp?  The SWR indicator in the RIG
> will measure the match between the rig and the amp. The SWR indicator in
> the AMP will measure the match between the rig and the feedline.


	Right.    That is what I am talking about.




> It is quite normal for different SWR indicators to give different
> readings on the same antenna.  Don't be alarmed unless one of them reads
> VERY high (much greater than 3:1).


	OK...  I am not as worried as I am curious why
	the rig sees a higher SWR with the amp on than
	with it off.   The amp tuning circuit plus antenna
	must present the rig with a different SWR than the
	antenna alone.   I am wondering why that happens
	- especially when it happens on 17m but not on
	15 or 10m when I size the same exact antenna in
	proportion up or down in size for the different
	bands?





>> * Does this have anything to do with working 17m
>>     opposed to another band?
>
> No.


	Shoot... another WAG misses the mark !    ;-)





> BTW -- FWIW, my Titan 425 amps, designed in the late '70s, work best on
> the WARC bands when I set the amp to the band BELOW the WARC band I want
> to work.


	OK... maybe I should try that, instead, and
	see what I get.
	
	What could be the harm in doing that?   After all,
	there is only so much smoke, so once it is out,
	the danger is over, right?     ;-)


	


> Another BTW -- the right way to tune a triode power amp is to drive it a
> bit below the power level needed for rated output, tune Tune and Load
> for maximum output, increase the drive only enough to get rated output
> (or lower power if you want) and re-peak Load and Tune.



		OK... I get that.



NEVER use ALC
> between the rig and the amp to set power level -- that is a recipe for
> massive splatter.


	I will remember that.   As this is Centurion
	and an Omni VII I am spared all the fuss and
	bother of ALC circuits.





AND -- a great way to tune a power amp is to use your
> paddle to send a series of dits, which reduces the stress on the tubes
> and the power supply, while still causing the amp to operate at its peak
> output level (and thus provide the cleanest tuning).



	I should do that.  I have just gotten into
	the easy habit of hitting the tune button
	and it lowers power to 17 watts so I guess
	I figured that was going easy on it.

	I do know pulse tuning is a preferred method.




>
> Before I got my KPA500, I occasionally used the Titan to get me to 200W
> on 30M. Two of my Titans are happy on 30M, but the oldest one, probably
> built before WARC bands were authorized, is not. I suspect that the
> input circuit is not sufficiently broadband to pass 10 MHz (I tried both
> 40M and 20M settings of the bandswitch), and in either position it
> seemed like something was overheating, even at only 200W out. That would
> be consistent with trying to run power through a resonant circuit
> outside of its design range.



	This was the sort of thing I was guessing
	at above.   I figured it was a WARC band and
	the amp would not tune as cleanly as on 20m
	and 15m.



		

> Remember that SWR is a very limited way to describe what's happening in
> a system -- as the late Dick Heyser said of frequency response, "it's
> like trying to write poetry with only one word in your vocabulary."



	Agreed.   And the examination prep books and other
	materials do a lousy job of explaining this.
	So many of my friends think the antenna is
	"resonant" when SWR is lowest, and that is all
	they ever look at.

	I know better, but I honestly don't know enough
	to say I fully understand all the rest that is
	involved.   Someday I will.  If I can learn to
	put the seat down, I can learn this, too, right?
	
	;-)


Thanks for the uptake.

------------------------- K8JHR -------------------
	
>
> 73, Jim K9YC
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