[TenTec] Centurian data points.

[Bob McGraw]

Depends on the dummy load.  Good quality loads stay very close to their 
R values when cold to hot.  While others will usually migrate up in R 
value.   The air cooled loads are more prone, from my experience, to 
change more and at a faster rate than liquid cooled loads.

I've three different loads, one is a Bird 1.5 kW forced air cooled load 
that is quite stable.   One can buy a nice new transceiver for what one 
of these costs.  And then there are the two "gallon bucket" loads with 
mineral oil or transformer oil. These do increase in R value about 10% 
from ambient to quite warm.  The one with transformer oil is more stable 
than the one with mineral oil.  There are a number of good quality used 
commercial loads on the market. 
https://www.nm3e.com/loadSampler.htm#LoadSampler

I've given thought to getting a new empty gallon paint can, making some 
fins from copper sheeting and soldering these around the can in order to 
improve conduction to the air.   That of course is one of my " 
'round-to-it" projects.

73

Bob, K4TAX

On 2/24/2021 8:48 AM, CARTER GRABARCZYK wrote:
>   What kind of dummy load? An off the wall idea, but when the "dummy load gets very warm", is it still 50 ohms - or is the resistance changing?
> 73,Carter   K8VT
>
>      On Tuesday, February 23, 2021, 2:00:25 PM EST, Ken Brown <kenradiobrown at gmail.com> wrote:
>   
>   Hi Bob,
>
>      Not sure exactly where your numbers are coming from. Is Pin your
> calculated Plate Power input using Plate Current and Plate Voltage meter
> readings from the amplifier? How are you measuring fwdWatts? The built in
> meter in the amplifier? Are you using any kind of RF wattmeter separate
> from the amplifier, such as a Bird 43 with a 2500H element? You mentioned
> an RF Voltmeter, have you used that yet. What kind of RF Voltmeter is it?
> Do you trust it's accuracy and flat frequency response on all of the HF
> bands? And is it high enough impedance to have negligible effect on the 50
> Ohm  system? If so measuring RF Volts directly at a good 50 Ohm
> non-inductive termination should be a good way to accurately determine RF
> power.
>
> Ken N6KB
>
> On Tue, Feb 23, 2021 at 7:48 AM Bob D. <ajamas.rn at gmail.com> wrote:
>
>> New to me Centurian.
>> I was a bit surprised to find a 15A and a 25A fuse.
>> 20 A x 2 is specified for 230V so I replaced them.
>> Total is the same :-)
>>
>> Here is what I see with a 50 Ohm dummy load and the Centurians meters.
>> The LED peak reading varied from 1.2 * to 2 * the "wd" meter.
>> Drive varies from 50 W to 100 W with lower on the higher bands.
>> Drive is Eagle via 18" coax and a 6' piece of RG213 to the dummy load.
>>
>> Band(CW end) m, Ig mA, Ip mA, fwd Watts?, Pin
>> 10 260 390 600 1100
>> 15 260 430 900 1200
>> 20 230 420 1100 1180
>> 40 200 500 1200 1400
>> 80 230 600 1200 1700
>> 160 250 600 900 1700
>>    Ep 2.8 kV at 600 mA
>>
>> Things don't add up.
>> 10 m 1100 W in 600 W out is not unreasonable
>> 15 m 1200 in and 900 out seems rather good but not impossible.
>> 20 m 1180 in and 1100 out is nonsense
>> 40 m 1400 in and 1200 out is  unbelievable
>> 80 m 1700 in 1200 out is not unreasonable
>> 160 m 1700 in and 900 out is a bit low but how efficient is this amp on
>> 160?
>>
>> Yes, the dummy load gets very warm.
>> Anodes glow nicely on 10 m so the input power is going somewhere :-)
>>
>> I suppose I'm going to have to dig out and check calibration on my RF
>> voltmeter and measure at the dummy load to have a good number for the
>> output. Will also have to study up on the metering circuitry to see why the
>> results are so weird.
>>
>> The manual says no more than 800 mA Ip. They must have used a different
>> transformer to get 800 mA!
>>
>> 73, -Bob ah7i
>>
>>
>> -do not look into LASER with remaining eye!
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