Can you hook up a Linear Amp to a Flex 3000

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How do I go about connecting an Amp. to my Flex 3000?
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David Kutiej

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Posted 3 years ago

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John

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ofcourse you can. What are you worried about ?
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David Kutiej

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Everything?  How do you tune the amp without a SWR/Power meter to set power for the different bands? Do you run it from radio to amp to antenna?
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Bill -VA3WTB

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you should have a good SWR meter in line. I use an Amaritron antenna tuner with a SWR meter built in.

so, Flex to amp, amp to meter,antenna into meter.
You can just run radio to amp and use the antenna tuner. But you really should have a meter to see what your power and SWR output is from the amp.
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David Kutiej

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Bill thank you for your quick response. You've made it sound simple and I will try it later today. I have a good SWR/Power Meter, it is a Kenwood SW-2000 that I was using with my Kenwood TS-2000. So far I really like the Flex, aside from some minor things like the amp I'm enjoying the radio.  THX.......David.
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Bill -VA3WTB

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make sure you set the tune power low to start, it is found under tx menue under setup.
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David Kutiej

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Bill, THX for the tip......David / KE7JHA
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John

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I suspect you are worried about the internal atu first of all ( switch it off ) and then the ptt from the flex to the amp. I use an old challenger 3 amp with a pair of 3cx800a7 tubes in it and have used a foot switch to key the amp. It works for me , but might not for you. In that case you can use the info on pages 5 and  6 of the user manual. I suggest you look at the amp first and see what it requires, then look at these pages.
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David Kutiej

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John, thank you, I understand the Bypass of the ATU, but you lost me on PTT part. I'll look into the manual like you suggest.
THX   David.
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Bill -VA3WTB

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Yes I have had an Amaritron amp connected to mine for 7 years.
Connect the amp to TX out on the Flex, that will key the amp. I recommend a keying buffer between the amp and the Flex.
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David Kutiej

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Bill,what is a keying buffer?  Where would I get one and how do I install it?
David.
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Ross - K9COX

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David, what amplifier do you have?
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David Kutiej

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Hello Ross, I have a Kenwood TL-922A....David / KE7JHA
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Ross - K9COX

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The Flex 3000 has relay contacts to actuate the amp keying line. A external buffer will not be required to interface with your TL-922 amp. Here are the Flex specs:
 (6) External Keying Line This keying line, which can be given a delay, can be used to key an external device such as a linear power amplifier or transverter. The external keying is provided by a relay closure to ground, with a rating of 250 VAC, 220 VDC at 2 A and with a 2.5 ms nominal switching time.
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Bill -VA3WTB

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Ross is right, in my case and yours the only reason to have a buffer is security against a possible voltage spike, but as long as things are working well you won't need it. Amaritron makes one. Here is a post with it.
https://community.flexradio.com/flexradio/topics/ameritron-arb-704-flex-6500-and-ameritron-al-80b-am...
(Edited)
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David Kutiej

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Thank you Bill, you've been most helpfull.    David / KE7JHA
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Steve W6SDM

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it sounds like you have it pretty well covered and have some great advice.  I ran my Flex 3000 for years with a Kenwood TL922-A amp.  You didn't ask but I will offer you some advice that nobody's mentioned yet since you seem new to running a linear.

1.  Double check all your grounds and make sure you have a central ground point with good connections.  This is a good practice anyway but even more important when you are running lots of power.

2.  Be prepared to use ferrites on various cabling throughout your station.  Where you may not have any noticeable stray RF at 100 watts, you just might with a KW.

3.  Tune your antenna to the best SWR before you put your linear on.  A little reflected power at 100 watts is  a whole lot at 1.5 KW.

Congrats on the linear. 
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David Kutiej

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Steve, thank you for your advice, I will use everything you suggested.  David / KE7JHA