Some companies are reportedly running 3500 to 3800 volts on their 3-500Z
amps. I'll stand by the tube manufacturers ratings of 4000 volts as being
absolute max with 3000 volts being typical. Plate current per tube should
not exceed 400 ma. Based on these values, I believe that Tentec has
designed the Centurion amplifier correctly and with a margin of safety and
longevity while others may have pushed things to the edge. The result is
likely shortened tube life, stressed components and the requirement for more
expensive components to withstand the higher voltage.
The real secret to keeping a 3-500Z amp alive is to carefully monitor and
control grid current. Proper tuning and loading is the key to success in
this area. There is no doubt or question, a pair of 3-500Z tubes can be run
to legal limit safely. Power supply components, high volume cooling and
high efficiency tank components are key areas to making the tubes work at
this level.
73
Bob, K4TAX
----- Original Message -----
From: <atrampler@att.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Saturday, January 17, 2009 3:32 PM
Subject: Re: [TenTec] Centurion question
> 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@Blomand.net>
> To: "Discussion of Ten-Tec Equipment" <tentec@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@att.net>
>> To: "Discussion of Ten-Tec Equipment" <tentec@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@pactor.com>
>>> To: "Discussion of Ten-Tec Equipment" <tentec@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
>>>>
>>>>
>>>>
>>>> _______________________________________________
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>>>
>>> _______________________________________________
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>>>
>>
>>
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