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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