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ND4JS
10-20-2010, 08:21 AM
I have been using a Ten Tec OMNI C with a clipperton L amp for some time now, but just recently noticed that there is a high swr between the rig and amp.
Ten Tec usually can handle high mismatches but I am wondering what I should do? Would it be a good idea to put a small antenna tuner between the rig and amp?

What would you do?

Thanks and 73 Jay KC4PHR

NN4RH
10-20-2010, 10:22 AM
I am no amplifier expert and I've never heard of "Clipperton L" amps, but it seems to me that amplfiers ought to be designed for 50 ohm input. If it is, it should match your 50 ohm output of the TenTec with nothing else needed

So if there's a high SWR between the two, that would indicate a problem. Sticking a tuner in there won't fix the problem.


Run the radio only to a 50 ohm dummy load using the same cable. If the SWR is good to the dummy load, then the problem is with the amplifier. If the SWR is bad then try a different cable. If it's good with a different cable, then the problem is with the cable. If it's still bad, the problem is with the radio.

That's as far as I go since I don't know anything about amplifier input circuits.

W8JI
10-20-2010, 11:29 AM
While you may have a cable problem, Dentron manufactured many amps without tuned input and without matching on the input to 50 ohms. The Clipperton falls into that category. Some of their amps that did have tuned inputs had wrong component values on some bands.

The best thing to do is add a tuned input system, but in some cases using the tuner in the rig or an external tuner will work..

http://www.w8ji.com/tuned_input_circuit.htm

KD1MA
10-20-2010, 01:23 PM
W8JI

As always, when I saw a reference to your site I immediately went to it to read what you had to say. At the bottom of the article, I came across this:

Using Tuners in Radios, or External Tuners, for Matching


If the amplifier contains a proper low-pass tuned input, and impedance is close but not quite right for your exciter, there is nothing wrong with using an external tuner.
May I assume that where you refer to 'external tuner', that that can also be interpreted as an internal radio tuner?

The reason I ask is that I use an OCF dipole that varies in SWR from 1.1 to 2.1. I need the full output of my rig to drive my amp and do that by using my internal tuner to fool my radio. I do not have a tuner after the amp because I have an Ameritron with a tuned input circuit and the mismatch is not great enough to bother it. Is this a safe assumption for me to make?

By the way, thanks for all your input. It is invaluable to those of us who were not fortunate enough to be trained in electronics but are still techno wannabes.

73

Bob KD1MA

W8JI
10-20-2010, 03:08 PM
There is nothing wrong with using the radio's tuner to touch up the match.

KL7AJ
10-20-2010, 03:16 PM
I usually keep an el cheapo antenna tuner around for taking care of such things. It can really do wonders. :)

Eric

VE3FMC
10-20-2010, 09:14 PM
There is nothing wrong with using the radio's tuner to touch up the match.

I do that every time I run my amp on 75 meters.

SB-200 and FT-950. SWR input is high on 75 Meters. Internal tuner makes the rig happy so it puts out the full power.

The rest of the bands between the amp and radio are pretty good so no need to use the internal tuner.

Remember those older amps like the SB-200 were built during the days of tube final rigs with PI networks. Those rigs would be happy if you loaded the rig, then the amp then reloaded the rig. I did that with the SB-200 and a TS-520.

N7WR
10-21-2010, 02:36 AM
While you may have a cable problem, Dentron manufactured many amps without tuned input and without matching on the input to 50 ohms. The Clipperton falls into that category. Some of their amps that did have tuned inputs had wrong component values on some bands.

The best thing to do is add a tuned input system, but in some cases using the tuner in the rig or an external tuner will work..

http://www.w8ji.com/tuned_input_circuit.htm

I agree. If your Clipperton does not have a tuned input you might look around for one as they are sometimes available. I had a no tuned input Clipperton once and the auto tuner in the exciter kept everything happy.

K7ZRZ
10-22-2010, 01:51 PM
Jay,

I haven't seen anyone mention the possibility of tubes that have suffered in some way, causing their input impedance to change. Each time I have had tube-problems in my Clipperton L, input-mismatch has been the primary indicator... well, other than the inability of the amp to produce the same kind of power that it once could.

I've read lots here and on other sites about what happens to a 572b tube when it starts to fail in its ability to make power. If this is a condition that has been "developing," then I would surely suspect bad tubes. And in which case, I agree that adding a tuner between the rig and amp is somewhat the wrong solution.

WS2L
10-23-2010, 11:28 AM
Although placing a tuner between the radio and the amp will take care of the problem I would be asking myself what is the cause of the high SWR. I had a similar problem once and it turned out that the solder job I did on the feedline going to the antenna tuner was not my best work. I swapped out the feedline and the problem was gone. It might be worth checking your feedline just to be sure it is not just a simple problem that can be easily fixed.

VE3FMC
10-23-2010, 12:03 PM
Although placing a tuner between the radio and the amp will take care of the problem I would be asking myself what is the cause of the high SWR. I had a similar problem once and it turned out that the solder job I did on the feedline going to the antenna tuner was not my best work. I swapped out the feedline and the problem was gone. It might be worth checking your feedline just to be sure it is not just a simple problem that can be easily fixed.

In my case there is no problems with coax cables etc.

It just has a high SWR input when on 75 meters. This causes the radio to drop back in power. The auto tuner takes care of that.

When I ran this SB-200 with a Kenwood TS-520 it would work fine because the Pin Network on the radio would be happy loading into the amp.

However, one day I put a manual tuner between the amp and the TS-520. The tuner could by pass the tuner.

With the tuner in line to take the SWR down to 1:1 between amp and radio the radio out put was higher, the out put of the amp was higher.

So using the tuner made the old hybrid happier.

Now it could be that I have a bad input tuning slug on the amp. The guy who did the Harbach mods on this amp played with the input tuning and could not get it any lower.

The tuner helps, yes it is not the proper solution but it works.

KE5BYM
12-30-2010, 11:46 PM
I have an Ameritron AL-811 (600 watts) connected to an Icom IC-756PROII and I use a Heil PR-781 microphone keyed with a foot switch. I have not had any problems with this for over 3 years, until lately. Now, when I key the rig by depressing the foot switch to transmit and let off of the foot switch to unkey the rig, the amplifier and radio remain in transmit mode. I also use the Ameritron ARB-704 amplifier buffer relay. I have tried reducing the power from the rig to the amp, and I have tried to reduce the amp output, and still no joy. FYI, I have the rig connected to a SteppIR 2-element beam with the transciever interface that automatically tunes the antenna for a near flat SWR. Any ideas as to the cause (and fix) to this problem? ANY help with this would be much appreciated. 73,

Darrell
KE5BYM

W8JI
12-31-2010, 10:47 AM
I have an Ameritron AL-811 (600 watts) connected to an Icom IC-756PROII and I use a Heil PR-781 microphone keyed with a foot switch. I have not had any problems with this for over 3 years, until lately. Now, when I key the rig by depressing the foot switch to transmit and let off of the foot switch to unkey the rig, the amplifier and radio remain in transmit mode. I also use the Ameritron ARB-704 amplifier buffer relay. I have tried reducing the power from the rig to the amp, and I have tried to reduce the amp output, and still no joy. FYI, I have the rig connected to a SteppIR 2-element beam with the transciever interface that automatically tunes the antenna for a near flat SWR. Any ideas as to the cause (and fix) to this problem? ANY help with this would be much appreciated. 73,

Darrell
KE5BYM

You have so much stuff connected to the radio that could be causing the problem it is hard to tell. It could be a bad foot switch, or a problem in the tuning interface, or in the wiring. Since the radio stays keyed, it is very unlikely to be in the amplifier or in the ARB system.

I would look at the foot switch, the Step IR interface, and other things that tell the radio to transmit.

73 Tom

WC5P
12-31-2010, 03:19 PM
SB-200 and FT-950. SWR input is high on 75 Meters. Internal tuner makes the rig happy so it puts out the full power.

The input circuit on the SB-200 has a slug tuned coil. You can adjust it for whatever part of the band you want. Perhaps the original kit builder adjusted it for 80 meter CW. Adjustment is shown in the assembly manual. You need a plastic hex tuning wand. Be careful, there is exposed HV with the covers off.

KM3F
12-31-2010, 08:09 PM
The Clipperton has little in the way of specific input matching.
Using an external tuner presents no issue.
It would be no different than if you could put that tuner inside the amplifier and able to adjust it with it's knobs out the front.
I have seen amplifier designs that use an "auto tuner" for the input circuit that can be purchused right out of a catalog for external use.
The total issue comes about because those old amp designs were used with tube final rigs that usually were run at there rated output so the mfger did not need to increase costs by including componants to present a 50 ohm match.
As well the old rigs usually did not have adjustable power out like todays units and needed to be less concerned about IMD and total harmonic output as opposed to todays radios and rules.

W8JI
12-31-2010, 11:43 PM
The Clipperton has little in the way of specific input matching.
Using an external tuner presents no issue.
It would be no different than if you could put that tuner inside the amplifier and able to adjust it with it's knobs out the front.
I have seen amplifier designs that use an "auto tuner" for the input circuit that can be purchused right out of a catalog for external use.
The total issue comes about because those old amp designs were used with tube final rigs that usually were run at there rated output so the mfger did not need to increase costs by including componants to present a 50 ohm match.
As well the old rigs usually did not have adjustable power out like todays units and needed to be less concerned about IMD and total harmonic output as opposed to todays radios and rules.

There is a big difference in performance depending on where the tuned input is, how long cables are, and what type of tuned input it is.


It is all explained here:

http://www.w8ji.com/tuned_input_circuit.htm

W0JBC
01-02-2011, 06:26 AM
Tom ,
I NEVER used a matching system ( in amateur ) between the exciter and the
amplifier . It was resolved in the exciter's pi- net and was 50 ohms .

The continuous ' key down ' after the foot switch was disengaged ,
makes me think of BASIC trouble shooting . Unplug the foot switch !

I have used the foot switch idea for many years . It still works to this day .

KE5BYM ( Darrell ) , resurrected this thread from October , 2010 .

That thread was discussing the Clipperton - L . Then went into the 811 .

They are not EVEN the same animals . :confused:

I agree , the foot switch would be the first place in the trouble-shooting
stage . Once it is dropped out , the system SHOULD unkey .
I just cannot fathom why anyone would put a ' TUNER ' between the
exciter and the amp ( normal amateur service ) ! :confused:

I am glad you are here to help .

J

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