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Re: [TenTec] Centurion loading

To: mike.hyder.n4nt@charter.net
Subject: Re: [TenTec] Centurion loading
From: Robert & Linda McGraw K4TAX <RMcGraw@Blomand.Net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Mon, 20 Jun 2005 20:54:48 -0500
List-post: <mailto:tentec@contesting.com>

With the antenna system already adjusted for 1:1 SWR or on a 50 ohm load, I 
switch the amp into the OPERATE mode and add a small bit of drive being 10 
to 20 watts or so, adjust TUNE and LOAD controls for max output.  Then 
increase drive while watching grid current.  If grid current gets to the Red 
line, adjust LOAD to keep grid current below the Red line on the meter which 
is 280 ma.  Add more drive as necessary and then adjust TUNE for maximum 
output and LOAD to keep grid current below the Red line.    Also, watch 
plate current and keep it below the heavy Black line which is 0.8 amps.

In my case, I also drive the Centurion with the Collins S-Line.  It will 
deliver some 130 watts output which will easily over drive the amp. Thus I 
can exceed 0.8 amps of plate current and at the same time 280 ma of grid 
current.  Also, I have a Heathkit SB-610 Monitor scope connected such that I 
can observe the trapezoid pattern and can see when the amp is adjusted 
correct, when it is under loaded, or when it is being over driven.  To this 
end, I am surprised today at the stations that are being operated without 
any type of monitoring system.  They are just using blind faith that their 
system is working correctly.  On the other hand, they have no clue as to 
what is actually going on.  And then there are those stations that generate 
lots of "buck shot" splatter and don't know it.  Just question one of them 
about it and you'll find out that it will be quickly blamed on the receiver 
of the station questioning such operation.

FYI, I started at the numbers listed on page 2-7 of the Tentec manual. 
Figure 2-4. Model 422 Tuning Chart.  To that end I have made my own chart 
which includes the adjusted final numbers on the Tentec 238 tuner for the 3 
different antennas that I use.  Along with these numbers are then the 
numbers for the amp.  So changing frequency or band is quite fast and 
accurate with minimum fiddling around.

Hope this helps.

Bob, K4TAX

----- Original Message ----- 
From: "Mike Hyder -N4NT-" <mike.hyder.n4nt@charter.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Monday, June 20, 2005 7:12 PM
Subject: Re: [TenTec] Centurion loading

>I am running the amp on 230 VAC.  I would think my antenna impedance is
> close to 50 ohms as I am using a Drake MN-2000 tuner and adjusting my W5GI
> mystery antenna for almost no reflected power.
> Based on your load control settings, by the time I get down to 3.5 MHz, it
> ought to be near 10.  The load control has an effect but here's what it 
> is:
> as I move it from 10 down toward zero, the output power decreases with no
> corresponding decrease in plate current.
> As an experiment, I just tuned the Centurion on 3.730 MHz.  Highest output
> is still obtained with the Load control on 10.  Power out is 1100 watts 
> but
> could be increased a tad without exceeding the plate current limitations.
> Thank you for your advices thus far.
> 73, Mike N4NT
> ----- Original Message ----- 
> From: "Robert & Linda McGraw K4TAX" <RMcGraw@Blomand.Net>
> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
> Sent: Monday, June 20, 2005 7:43 PM
> Subject: Re: [TenTec] Centurion loading
> Depending on antenna/load characteristics, being 50 ohms resistive, or 
> close
> to 50 ohms with some amount of reactance, the loading control on the amp
> should be about #4 at 4.0 MHz, #6 at 3.8 MHz, and  # 8 at 3.6 MHz.  Tune
> should be about #4 at 4.0 MHz, #5 at 3.8 MHz and #6 at 3.6 MHz.   The load
> control definitely has noted effect on 80/75M.
> My amp was purchased new from Tentec in March of 1996.  No updates 
> applied.
> Still running original tubes with full rated output power.  The Paragon II
> or the Omni VI+ will drive it to full rated power.
> Make sure you know what your load is.  Power output on 75M should be 1200
> watts or more.  Also are you running the amp on 230 VAC?  or 115 VAC?
> Unless you have a really stiff 115 VAC service, the regulation and power
> output will suffer.  It is not recommended to run the amp on 115 VAC
> service.
> 73
> Bob, K4TAX
> ----- Original Message ----- 
> From: "Mike Hyder -N4NT-" <mike.hyder.n4nt@charter.net>
> To: "Ten-Tec Reflector" <tentec@contesting.com>
> Sent: Monday, June 20, 2005 4:44 PM
> Subject: [TenTec] Centurion loading
>> I'm new to this Centurion thing and have a couple of questions:
>> My loading control does not seem to have much effect on 80 meters.  I
>> believe the amplifier acts as if it does not have sufficient load
>> capacitance.  I base this on my finding that I can never create too much
>> grid current and that the maximum output occurs with the Load control set
>> on
>> 10, which I assume is maximum capacitance.  If my assumptions are wrong,
>> please tell me.
>> I purchased the amplifier new from Ten-Tec in September 2003.  Can 
>> someone
>> tell me if there have been updates to this amplifier centered around the
>> load capacitance?  Are there modifications suggested on the same subject?
>> Thanks and 73,
>> Mike N4NT
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