Centaur 411 Amp

[Paul, Wv3j]

After reading the Article in CQ and observations from other users (and as
one who has been well satisfied with Ten Tec's gear and service) I ordered
one of the demo Centaur 411 amps.  I am now about half way through the
month's evlauation period.  The amp was clean inside and humidity was low.
I warmed it up several minuits before beginninig to check it out into my kW
dummy load and through my 238 tunner to an 80 Mtr loop antenna. I had
several problems right from the start:

        A loud THUNK on power up.        

        Frequent arcing of the plate tuning capacitor.
        
        Low output indicated by the 411's and 238's wattmeters as follows:

                f       Load    Tune    Ant     P (411)   P (238)  Notes

                1850    10      7       loop    475       600     80mA grid    

                3500    8.5     3.5     dummy   450       500

                3670    5       3       loop    450       500     @1.6 kv

                4000    1       2.5     loop    425       <500  

                7.125   9       1.5     loop    475       500    1.6 kv,
100mAg, 5000mAp

                14.200  7       1       dummy   400       450    same w/ loop

                21.200  7.8     1       dummy   250       150    

Post conversion 28.100  7       1       dummy   50         40   100w in,
120mAg, 400mAp

(The old SB 200 loaded all these frequencies easily with no arcing and with
full power indicated by the 238 (except 160 meters, which it was not
designed to do)).  I thought maybe the 15 meter low pass filter might be the
problem particularly on 15 mtrs, so I got the 10 mtr conversion from Ten Tec
and installed it.  Unfortunately things remain as tabulated above, difficult
to get a dip on 20 mtrs and above, with poorer  output as frequency is raised.

Did I get an amp with bad tubes for my 5% demo savings or did I get a bad
amp?  If the tubes are bad did the former operator of this demo amp maybe
ruin them and maybe also arc the cap plates so much that they are now too
close at melted edges?  I'd have thought a demo would have been gone over a
time or two more than a new one.  I was prepared for (and not alarmed by)
the small scratches and paint chips, but not for sub-standard performance.  

I'm sure Ten Tec will make good on this as they have always done, but it is
the beginning of the weekend, and Christmas shipping nightmare to boot.
I'll call them Monday, but meantime I'd welcome comments from any of you as
to the probable nature of these problems.

Thanks and Christmas greetings too all.

73,

Paul Helbert - Wv3j

              


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