Re: [TenTec] Ten Tec Centaur 411 10m Mod Needed

["Bob McGraw - K4TAX" <RMcGraw@Blomand.net>]

This amp does not have a tuned input but does have a 250 ohm 25W swamping 
resistor terminating the input, and electrically located on the output of 
the 15 meter filter.    The "15 meter filter" is a low pass input filter to 
prevent operation above 22 MHz.  When replaced with the designed 12M/10M 
filter, having a higher cut-off frequency,  it allows operation up to 30 
MHz.  Being a LP filter it would naturally attenuate any frequency above the 
design cut-off frequency while passing frequencies below the cut-off 
frequency.
The output network is a Pi design with a Q of about 12 depending on band. 
There is no output filter for spurious attenuation other than what is 
provided by Pi network attenuation.
73
Bob, K4TAX




----- Original Message ----- 
From: "Rick - DJ0IP / NJ0IP" <Rick@DJ0IP.de>
To: "'Discussion of Ten-Tec Equipment'" <tentec@contesting.com>
Sent: Friday, February 14, 2014 1:36 AM
Subject: Re: [TenTec] Ten Tec Centaur 411 10m Mod Needed


> Though Brian is correct, it is still bad practice to do this because it 
> does
> cause additional distortion in your signal.
> If you use an input filter rather than just direct coupling (with or 
> without
> a swamping resistor), it improves linearity about 10dB.  This means your
> signal will be broader on the band than it would be if the linear were 
> wired
> correctly.
>
> Although many of the first amplifiers did that when the first SSB linear
> amplifiers came out, we quickly began adding input filters to our
> amplifiers.  There is always a cost for cutting corners!
>
> BTW, at first I also made the same assumption Jim made.
> I thought he removed the output filter which would be the case for a
> transistor amplifier.
> Silly me; I forgot that the output side (here) is a Pi network and all you
> have is taps to the coil.
> Jim, we're getting' old!
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Brian
> Carling
> Sent: Friday, February 14, 2014 5:13 AM
> To: Discussion of Ten-Tec Equipment
> Cc: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Ten Tec Centaur 411 10m Mod Needed
>
> The absence of a low pass filter on the input stage of a linear amplifier
> doesn't always mean that you will automatically have unacceptable 
> harmonics.
> Radio amateurs have use linear amplifiers for years with a 50 ohm or 200 
> ohm
> swamping resistor on the input at the cathode of the amplifier whether 
> then
> a low pass tuned filter.
>
> You may very well be right there, depending on the design of the 
> amplifier.
> I have not looked at the circuit all taken a measurements.
>
> Best regards - Bry Carling
>
>
>
> > On Feb 13, 2014, at 9:44 PM, "Bob McGraw - K4TAX" <RMcGraw@Blomand.net>
> wrote:
> > The filter is a Low Pass filter with a nominal cut-off at about 23 MHz or
> slightly above 15M.  As designed this prevents operation above this
> frequency being on the 12/10M  bands.  This filter also provides 
> attenuation
> of harmonics above the designed cut-off frequency.  Now with the 12/10M
> filter installed the cut-off is raised to about 32 MHz thus allowing
> operation on 12/10M and yet  still providing adequate attenuation of
> harmonics above that frequency.
> > Removing the filter and replacing it with a jumper will allow the amp to
> work on 12/10M but WILL NOT provide ANY harmonic attenuation.   Any
> harmonics, i.e. 2nd, 3rd, 4th,  could fall into one of the Public Service
> bands.  Should interference occur and the user complain to the FCC, a
> written explanation by the operator will be required.  Frankly, in this
> case, I can't think of an explanation that would be acceptable.  Just
> remember, it is your amp and your license.
> > 73
> > Bob, K4TAX
> >
> >
> > ----- Original Message ----- From: <w8au@sssnet.com>
> > To: <tentec@contesting.com>
> > Sent: Thursday, February 13, 2014 8:06 PM
> > Subject: Re: [TenTec] Ten Tec Centaur 411 10m Mod Needed
> >
> >
> > > At 02:48 PM 2/13/2014, Kris Merschrod wrote:
> > > > I did the mod from the schematic and parts that T-T sent on a perfboard
> - it really isn't much, but, before hand,  I pulled the 15 meter filter 
> and
> put in a jumper wire - it worked like a charm w/o the filter - I am not 
> sure
> what the harmonics on that looked like - others can do the hi-tech work 
> :>)
> > > Ooops... there goes the FCC type approval.. ;-)  (hope your antenna was
> selective)
> > > Perry   w8au
> > >
> > >
> > >
> > >
> > >
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