[TenTec] Ten-Tec 411 Centaur Amp Problem

Mon May 31 19:58:04 PDT 2010

Good evening Mike and Duane,

I have tried two different alternatives to the short coax 1) 3 foot #213, 
and 2) 25 feet or so of RG 58, and not a bit of change in the SWR.  I havbe 
not tried the whittling down foot by foot b/c I am convinced that the 
problem just was not in the design.  I need to find the problem in the 411.

The observation that there is only a 25 ohm resister in parallel with the 
THREE 811s seems to be too simple, but perhaps elegant.  If tghat is the 
case though, thenthere should be similar mismatches on other bands.

Kris KM2KM
Merschrod
123 Warren Road
Ithaca, NY 14850
www.merschrod.net
----- Original Message ----- 
From: "Duane Calvin" <ac5aa1 at gmail.com>
To: "'Discussion of Ten-Tec Equipment'" <tentec at contesting.com>
Sent: Monday, May 31, 2010 10:36 PM
Subject: Re: [TenTec] Ten-Tec 411 Centaur Amp Problem

> Why not just try a different length of coax and see what happens - that is
> an easy experiment.
>
> 73,  Duane
>
> Duane Calvin, AC5AA
> Austin, Texas
> www.ac5aa.com
>
>
> -----Original Message-----
> From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
> On Behalf Of Kris Merschrod
> Sent: Monday, May 31, 2010 9:31 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Ten-Tec 411 Centaur Amp Problem
>
> Good evening,  I am still fiddling and pondering the observations on this
> problem.  Gary's observation means that no matter the band the input
> impedance is the same except for the "intervention" of the coax between 
> the
> exciter and the AMP.  That is hard to believe, b/c my 8"jumper cable seems
> to keep the 160, 80 and 20 meter input "happy" (No SWR)  but on 40 it all
> goes to "pot."
>
> I can't believe that TT built non-matching rigs in the 1990s.  Something
> else has to be wrong.
>
> Kris KM2KM
> Merschrod
> 123 Warren Road
> Ithaca, NY 14850
> www.merschrod.net
> ----- Original Message ----- 
> From: "CSM(r) Gary Huber" <glhuber at msn.com>
> To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
> Sent: Monday, May 31, 2010 10:16 PM
> Subject: Re: [TenTec] Ten-Tec 411 Centaur Amp Problem
>
>
>> In the case of the Centaur 411, the input is simply a 25 Ohm resistor in
>> parallel with the cathodes of the 4 811s (which are also in parallel).
>>
>> The input load impedance of the Centaur is always less than 25 Ohms and
>> thus
>> the length of input coaxial cable plays a significant role in 
>> transforming
>> the SWR for the driving solid state transmitter.
>>
>> 73,
>>
>> Gary - AB9M
>>
>> (NOT an E.E.)
>>
>> --------------------------------------------------
>> From: <wow_chf at hotmail.com>
>> Sent: Monday, May 31, 2010 8:32 PM
>> To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
>> Subject: Re: [TenTec] Ten-Tec 411 Centaur  Amp Problem
>>
>>> Yes indeed.  In fact, there were two different lengths in the Collins
>>> 30S1
>>> manual, one for their transceiver and one for their transmitter.
>>>
>>> In my article the explanation as to why this works is as follows:
>>>
>>> "In cases involving RF signals, some time will pass during the 'round
>>> trip
>>> of the reflected energy and the phase of the reflection will also depend
>>> upon this length of time. Imagine that a resistor in a black box is at
>>> the
>>> end of a length of cable. From the outside world this length of cable
>>> will
>>> give the reflection from the resistor a phase shift since the signal 
>>> must
>>> make a round trip through the length. If a 100 ohm resistor has an SWR 
>>> of
>>> 2,
>>> a cable long enough to invert the signal after the round trip will make
>>> it
>>> look like a 25 ohm resistor, also with an SWR of 2 but with inversion (a
>>> cable with a multiple of 1/4 wavelength would do the trick). Since the
>>> impedance looking into this black box is a function of the SWR and the
>>> cable
>>> length, it can be seen that intentionally mismatched lines can be used 
>>> to
>>> transform one impedance into another. Notice that the 1/4 wave cable
>>> inverts
>>> the impedance and preserves the SWR. This impedance inversion may be 
>>> used
>>> to
>>> match two impedances at a particular frequency by connecting them with a
>>> 1/4
>>> wave cable with an impedance equal to the geometric mean of the two
>>> impedances. (The geometric mean is the square-root of their product.) A
>>> 50
>>> ohm, 1/4 wave cable will match a 25 ohm source to a 100 ohm load :
>>> sqrt(25
>>> x
>>> 100) = 50. Of course, it is not always easy to find the desired 
>>> impedance
>>> cable!
>>>
>>> Multiples of 1/2 wavelength will give enough delay that the reflection 
>>> is
>>> not inverted and the impedance will be the same as the load. Such cables
>>> may
>>> be used to transfer the load impedance to a remote location without
>>> changing
>>> its value (at one frequency).
>>>
>>> Other cable lengths will transform an impedance which differs from the
>>> cable's impedance with a reactive component. If the load is a lower
>>> impedance than the cable, a length below 1/4 wave will have an inductive
>>> component and above 1/4 (but below 1/2) wave a capacitive component. If
>>> the
>>> load is a higher impedance than the cable, the reverse is true. Above 
>>> 1/2
>>> wavelength, the reactance will alternately look capacitive and inductive
>>> in
>>> 1/4 wave multiples. This reactance will combine with the load's 
>>> reactance
>>> and offers the possibility of resonating the reactive component of the
>>> load.
>>> Therefore, a cable with the "right" length and impedance can match a
>>> source
>>> and load with different resistance and reactance values. Obviously, 
>>> these
>>> calculations can become quite involved and most engineers resort to a
>>> Smith
>>> chart, a computer program or perhaps the most common method, trial and
>>> error
>>> with a SWR meter or return loss bridge!"
>>>
>>> Sorry for so much bandwidth.
>>>
>>> 73 and Happy DXing,
>>>
>>> Mike
>>> W2AJI
>>>
>>>
>>>
>>> -------------------------------------------------
>>> From: "James Duffer" <dufferjames at hotmail.com>
>>> Sent: Monday, May 31, 2010 8:15 PM
>>> To: "Ten Tec" <tentec at contesting.com>
>>> Subject: Re: [TenTec] Ten-Tec 411 Centaur  Amp Problem
>>>
>>>>
>>>> I recall from some Collins manual for their amp 30S1 they specified a
>>>> length for the coaxial cable between the KWM-2 and the amp.  In that
>>>> case
>>>> that was their fix.
>>>>
>>>> Jim de wd4air
>>>>
>>>>> From: k9yc at audiosystemsgroup.com
>>>>> To: tentec at contesting.com
>>>>> Date: Mon, 31 May 2010 13:19:38 -0700
>>>>> Subject: Re: [TenTec] Ten-Tec 411 Centaur  Amp Problem
>>>>>
>>>>> On Mon, 31 May 2010 15:55:31 -0400, wow_chf at hotmail.com wrote:
>>>>>
>>>>> >I submitted the article draft to QST, and it was questioned by the
>>>>> >Technical
>>>>> >Review folks, and although I have been published in QST before, they
>>>>> >could
>>>>> >not see how this would "transform" the apparent input SWR.
>>>>>
>>>>> Because it's a POOR fix for the fundamental problem, which is 
>>>>> something
>>>>> wrong
>>>>> in the input circuit of the power amp causing a mismatch. The proper
>>>>> fix
>>>>> is
>>>>> to find and correct the problem in the input circuit. Adding coax is a
>>>>> band-
>>>>> aid.
>>>>>
>>>>> 73,
>>>>>
>>>>> Jim K9YC
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> TenTec mailing list
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>>>>
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