Centaur 411

[Duane Calvin]

About a week ago I posted measurements made on my new Centaur 
showing that the power output appeared low from 20m upwards.  Discussion 
with Scott and some offline notes prompted me to debug my ICOM 765's 
auto-tuner to improve the match between the rig and the amp.  Apparently 
the 765 starts power foldback at about 1.5:1 SWR.  Below are resulting 
measurements made while driving the amp to full input spec.  Performance 
looks considerably better.  Close enough to spec that I'm not going to 
worry about it, and will happily hold on to my 411.
     On the arcing problem - I have not had this happen since the first 
round of measurements - and I've done several since.  It must have been 
genuine factory dust on the capacitor plates that got vaporized (HI!).  
QSK - great!  Thunk - put your SWR bridge on the cabinet top - solves 
that problem.  (If you're really concerned about inrush, check out the 
ARRL handbook for some simple solutions, one involving a single relay.) 
 On loading techniques, it pays to heed the manual (and Doug DeMaw's) 
instructions about "tightening" up the loading and paying attention to 
the grid current.  Increasing the loading coupling allows you to apply 
more power without causing the grid current to take off.
     Fan noise - well, I'm still sensitive to this, but I plan to hold 
on to the amp and either a) wait for a factory mod to quiet this down, 
or, b) do my own mod later on.  I'll try to get used to it for now, but 
certainly not without using headphones!  I know someone in our company's 
thermal lab . . .
     Thanks to those of you who sent suggestions and encouragement - 
this kind of help on a reflector is nice to find.  Hopefully, I can 
contribute similarly in the future.


	Power Meas.(W)	  XMTR Meas.				
Freq	Centaur	Bird	SWR	Drive 	Arc?	Ig (mA)	Ip (mA)
----    ------- ----    -----   -----   ----    -----   -----
14000	480	631	1.0:1	100	No	115	630
14350	550	661	1.1:1	110	No	125	650

18100	490	491	1.1:1	80	No	150	750		

21000	480	535	1.1:1	110	No	110	750

24900	450	550	1.1:1	90	No	110	850	

28000	420	580	1.1:1	100	No	100	850		

(Driving resistive 1KW dummy load)

73,  Duane  		
----------------------------------------------------
Duane Calvin, AC5AA
email:  ac5aa@juno.com  -or-  duanec@prodigy.net
packet: ac5aa@w5syt.#aus.tx.noam

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