[TenTec] Centurion question

Sat Jan 17 16:32:42 EST 2009

Bob et alia

I agree whole-heartedly that the Centurion in no way needs the transformer 
of HV PS replaced, unless it has failed.  I provided the link only to show 
what one man has done, and to show that yes, higher voltage can be run on 
then, but it is only with a purpose, such as moving the amp into a truly 
differetn power class.  I think the Henry 3K-A runs a couple of 3-500Zs or 
3-500ZGs; I Elmered a pretty wealthy guy around 1980 who bought the 2K-4 
Classic X...before he had his license...and with the higher voltage, 
somewhat more rugged tank components and cooling it was a legal limit amp.

You are right Bob about the reliability of the Centurion.  I am going to 
send mine back at some point because I had a loose bolt or two on my 
vertical and arced the plate capacitor on 20 meters severely...enough that I 
went in with a file to smooth it out to keep it form arcing after I fixed 
the antenna.  It still arcs every once in a while.  Also, I notice that on 
40 meters in particular, into a dummy load or antenna, my loading is 
generally up close to 10...if I'm only running 600 or 700 watts, it may be 
10.

I don't know if there are fixed capacitors in the circuit on 40, but if they 
are I wonder if they have strayed...

So I'll send it back, and also of course have the meters adjusted.

I love the amp though...it was just me not checking factory-assembled parts 
when I installed this vertical.

73,
Art

----- Original Message ----- 
From: "Bob McGraw - K4TAX" <RMcGraw at Blomand.net>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Saturday, January 17, 2009 8:16 AM
Subject: Re: [TenTec] Centurion question

> Phil, Art and all;
>
> The Centurion I have was purchased new by me from Tentec in March of '96.
> It has the original tubes, transformers, capacitors, diodes and such.  I
> find it to be a very reliable amp and a work horse.  Consistently, it
> delivers some total 1400 watts output as measured on 2 different watt
> meters.  Now, although it is rated at 1300 watts output SSB, do remember
> that the 1400 watts I measure does include about 100 watts of drive power
> from the transceiver.  That power also appears as part of the output.
>
> Transformer wise, I find it to be quite solid.  Yes, the voltage per the
> manual shows 3100 to 2600 and is a "no load" to "full load" condition.  No
> load condition will never exist except during stand-by as the tubes are at
> full cut-off.  Full load condition will exist on TUNE only with carrier
> which will net about 2600 volts at 0.8A of plate current for 2080 watts
> input developing an output of 1300 watts {amp power less drive power} for
> 62.5% efficiency.
>
> For SSB, the duty cycle being very short, the Keyed voltage should be 
> about
> 2900 volts {tubes at idle current of 100 ma} and with voice the voltage
> drops another 100 to 200 volts.  This is the result of the capacitance in
> the power supply holding the voltage very solid.  On a 230 VAC source, my
> amp is running 2900 this morning, KEYED {no signal} it drops about 100 
> volts
> to 2800, and with voice I can see about another 100 volt drop.  This is a
> regulation of 93.1%.  Very acceptable in my opinion and experience.
>
> I would say that replacement of the transformer is totally un-necessary
> unless one has failed.  As to going to higher voltage, the 3-500Z is rated
> at 4000 volts maximum and 3000 volts typical.  Based on my measurement,
> observation and results, higher voltage is not necessary.  In conclusion,
> this is not a "legal limit" amp but with my results the station is capable
> of 1400 watts as opposed to the 1500 watts legal limit.
>
> Regarding duty cycle, I frequently run AM at 250 watts of carrier output
> with no problems.  I also run full QSK CW at 750 watts output and 
> experience
> excellent results.  For a desk top amp, the Centurion is a very good buy.
> The input and drive impedance nets a 1.5 : 1 SWR on all bands and
> frequencies except 160M where it will be 2.0 :1 at the band extremes. Most
> transceivers tolerate these value very successfully and thus provide
> adequate drive to the amp.
>
> I'd say the biggest fault that might exist with the Centurion is largely
> improper operation.  Having repaired a few of these for other folks, these
> faults are likely the result of poor antenna load conditions, either wrong
> antenna for frequency, or antenna with suddenly high SWR either from a
> shorted line or open circuit.  Changing the band switch while tuning is
> always one that produces a failure mode, hot switching between RX/TX due 
> to
> improper transceiver interface means, and of course lightning strikes 
> where
> little if anything survives.
>
> All in all, the Centurion is a well designed amp and a day-in and day-out
> work horse.
>
> 73
> Bob, K4TAX
>
> ----- Original Message ----- 
> From: <atrampler at att.net>
> To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
> Sent: Saturday, January 17, 2009 4:37 AM
> Subject: Re: [TenTec] Centurion question
>
>
>> Phil,
>>
>> You can read about people replacing the transformer in the Centurion
>> (there
>> was something about TT losing the guy who made their transformers/getting
>> them from somebody else) but I think the issue you are talking about is
>> one
>> of design, not of robustness.
>>
>> I pull a KW (and a bit more if I wanted to) easily from the unit.  If the
>> RF
>> deck were designed for more power, then yes, running a higher plate
>> voltate
>> would or could make sense to increase the power out.  Some Henry's ran 
>> 4KV
>> key up, and produced about 2KW out from a pair of 3-500Zs.
>>
>> In case you really want to, look here:
>>
>> http://hamradiomarket.com/articles/Ten%20Tec%20Centurion.htm
>>
>> The neat thing about the Centurion is that the plate transformer is just
>> that...the plate transformer, not supplying filament or other voltages.
>> So
>> this fellow modified his by building an external 4KV supply.  He claims
>> the
>> RF deck is nice and robust and good for this and therefore the unit
>> becomes
>> a legal limit amp (he was pulling 1700 watts out of it), but I don't feel
>> comfortable with that.  That's just me...I'm not an engineer.
>>
>> So I hope this short answer was worth it.  One nice thing about the
>> modification he did is that the HV PS now sits on the floor away from the
>> amp which is made considerably lighter.
>>
>> 73,
>> Art, K0RO
>>
>>
>> ----- Original Message ----- 
>> From: "Phil Sussman" <psussman at pactor.com>
>> To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
>> Sent: Saturday, January 17, 2009 3:10 AM
>> Subject: [TenTec] Centurion question
>>
>>
>>> Greetings,
>>>
>>> I am considering the purchase of a Centurion HF amp. After reviewing the
>>> specs,
>>> I'm wondering about the 3100vdc supply dropping to 2600vdc under 'full'
>>> load.
>>> Is the power supply heavy enough? My past experience with dual 3x500Z's
>>> has
>>> plate voltage holding at 2900vdc to 3000vdc typically under full load
>>> conditions.
>>>
>>> Comments certainly welcome.
>>>
>>> Thanks,
>>>
>>> de Phil - N8PS
>>>
>>>
>>>
>>> _______________________________________________
>>> TenTec mailing list
>>> TenTec at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>>
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>
>
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