Centaur 411 Amp

Chuck (Jack) Hawley c-hawley@uiuc.edu
Sun, 22 Dec 1996 09:29:47 -0600

Paul, Wv3j wrote:
> 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.

So not we know that it doesn't have a step start....not unusual though
for this price class but too bad anyway. I wonder if the (cheap), in
series with the line current, thermister type of current limiting would
be a good idea for these inexpensive power supplies (Astrons), amps and
>         Frequent arcing of the plate tuning capacitor.

That's what Doug DeMaw said in the CQ "review" but I think he should
have gone on to say "don't buy it". I pretty much decided to drop CQ
magazine based on the superficial reviews that McCoy and DeMaw put out.
They are both nice guys it seems and pretty smart cookies but if they
won't be knowlegeable or straight about what they are looking at
(subconsciously or otherwise) then who needs to pay 'em to do product
reviews for the rest of us.

>         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

I'm not qualified to comment on the poor performance but I'm sorry to
learn about these additional questions about the amp. I guess I would be
wondering about the tubes also.
> (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 woulda been disturbed by the scratches and chips. Is there a simple
cover that can be replaced for 10 or 15 bucks that took most of the
scratches? I always figured that I would be safe buying a TT because
they could supply me with a new cover for most of their stuff.
> 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

Good luck. It's really difficult to deal with these well meaning, nice
people when they just don't have the same technical rules and standards
that you have. Although I'm sure that your reduced output on the higher
bands is below their standards, I am reminded of the guys I know who
tried in vain to like the Omni 5's and 6's that drifted or jumped 30,
50, or 80 hertz from night to night on 75 Meter phone. It's not that
important.....but darn it...it's frustrating when you spend a couple of
hours to get it really close and then it's off again the next night. The
factory thinks you're nuts to be nit picking like this....so eventually
these guys drifted back to rice boxes that always end up at the same +/-
3 hertz every night. Now we can do that in this country and it shouldn't
matter why we want it.....the rest of the world seems to think it's
important enough to do it and is willing to sell us expensive tcxo's.
Now I know I'm going to hear a bunch of stuff about phase noise and
crystal controlled oscillators....can't we do it with more stability?
...even though it doesn't matter? I guess not....not with voltage
controlled capacitors pulling the crystals and microprocessors
correcting the master oscillator at least.

I really want to say some more about my brain damaged TT auto tuner but
it's discontinued and nobody seems to know anything about it, so I won't
mention it.

Paul, is there room for a bigger tune cap in there? Just wondering.

73, Chuck, KE9UW

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