Yaesu FT-900 to Yaesu FL-2100B amp wiring questions?

Discussion in 'Amateur Radio Amplifiers' started by KE4CIJ, Jun 8, 2014.

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  1. KE4CIJ

    KE4CIJ Ham Member QRZ Page

    Recently, I picked up a fairly nice or seems nice FL-2100B, regardless of what my friend suggested about the amp I still think it was a good find, he simply said the Amp was Junk, he dislikes the FL2100 because of a bad melt down he had several years ago, swore them off and bought an Ameritron.

    Okay I also use an older FT900 and I would like to use the Amp with my rig. I know or at least I think I know I will need some RCA type connectors for the radio to the amp, and here's where I am lost.

    Okay do I used the ALC hookup on the Radio? Or do I used the PTT out on the radio? Or What do I use and how?
    On the back of the linear I see 4 connections, one being a ground, I am almost certain I'd use that with the RCA but where does the conductor go? When I speak of the ground I am not talking about the main grounding post, I am talking about the one on the amp on the back left bottom one of 4 connections I can see.

    I am not even sure this is a good combo, 900 and FL-2100 into a ground mounted vertical at the moment, but from all accounts it should be fine once I become acquainted with the amp tuning procedure.

    Believe this or not, and perhaps I didn't pose the right questions to Google but I couldn't find a single bit of how to on hooking up this amp using an 900 radio.

    Any help would be most appreciated being this is my first experience with the FL-2100B and I hope it does not turn out like my friends experience with his. He owned two and both of them turned into melted heaps of ruin. I made the comment to him, I thought it was Operator Error more than the amps fault which further fueled his hate for the FL linear!

    It's Sunday, I got a little winded on this but all I need is a basic idea of how to wire the radio to the amp that will give the best over all results without Melt downs please!

    thanks in advance,
    God Bless to one and all!

  2. G4FUT

    G4FUT XML Subscriber QRZ Page

    I have neither of these rigs, BUT....I strongly advise connecting a "soft-start" circuitry between the FT900 and the FL2100. the relay voltages of these tube linear are generally far to high for the more modern semi-comductor transmitters and will fry the relay on the TXs.

    I fried the relay in my ICOM 718 when I connected it to my home-made 2 x 813 linear.:mad:
  3. KE4CIJ

    KE4CIJ Ham Member QRZ Page

    Thanks for the reply and suggestion.
  4. KA0E

    KA0E Ham Member QRZ Page

    I used an Ameritron ARB-704 to key the FL2100B. An interface type device they sell to isolate keying voltages
    from the rig you using...You will want to use short, shielded RCA type cables for the connection.

    I found an adapter on e-bay that went from RCA to screw terminals. That made it easy to move around/unhook
    without messing with a screw driver on the amp end of it...I think it's the outside 2 screws that key the rig, not
    sure of my memory though...hi...don't trust me on that one..

    My rig only ran about 90 watts, so I never did hook up the ALC. Maybe should have but never seemed to have
    any problems, just backing the drive down a little.
  5. KA0E

    KA0E Ham Member QRZ Page

    Got to thinking, I have some pics still from when I sold the amp..It is the 2 outside screws that key the amp..

    Attached Files:

  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, on the FL-2100, the RY screw terminal and either one of the "E" (earth) terminals is used to key the amp from the transceiver.

    The FT-900 is a slick little rig and its internal amplifier keying relay CAN handle the keying requirements of the FL-2100 just fine. No outboard keying interface needed. The internal Yaesu relay can handle 220Vdc at 300 mA, which is way more than the FL-2100 relay runs. I would NOT recommend an external keying interface for that particular rig.

    However, the internal amp keying relay is shipped from the factory with that internal relay switched OFF. You have to switch it on, to make it key an amplifier from the TX GND RCA jack on its rear panel. You turn it on by sliding switch S2001 which is accessible through a hole in the bottom of the rig.

    I had an FT-900 and used it with plenty of FL-2100s. No special interface required.
  7. KA0E

    KA0E Ham Member QRZ Page

    WB2WIK is surely right...I guess I thought I read FT-990....If I remember correctly the amp call out is 100mA

    No...not right, I am now thinking of my AL-82.........................Nevermind, maybe some coffee would help:eek:
    Last edited: Jun 9, 2014
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Many older rigs can key amps directly with no interface required, because they were simply designed to do that. The FT-900, although all solid state and not too old, is in that category. Has a very robust keying relay, but must be activated to use it.

    My 1990-vintage TS-850S is like that, too: It can key almost anything "directly," once you activate that relay.
  9. KE4CIJ

    KE4CIJ Ham Member QRZ Page

    same as threard

    Thank you guys, all of you! Okay now which connection on the 900? I got that I need to turn on the dip on the FT 900 and I can use RCA connections on the amp. I scored that by robbing and older speaker I had. I found some shielded cable I had for smaller work so I made that connector in the picture above. On the back of the 900 is a ton of connections, so that is sort of confusing and some are shown as Din, and due to the fact I have never used any amp on the 900, sort of lost there. Someone told me to use the PTT on the back, others said to use some Din plug connection and then another said it was an RCA! So more confused by all that...

    Oh and I certainly know all about the coffee!

    The connection I think or believe I should use is the TX Ground on the back of the FT900 is that correct?
    I could if need be use the ALC but as said I don't believe It's needed, that might be different once I get it up and running however.
    Last edited: Jun 10, 2014
  10. KE4CIJ

    KE4CIJ Ham Member QRZ Page

    I was questioning myself on which connection on the back of the Rig I used, being FT-900. I put that in my post. I believe it should be the TX ground is that correct.
    Okay so I use and RCA, center to the connection on the amp, then the ground to the ground on the amp.

    Now if I wanted to use the ALC, do I also connect it the same way, go from RCA center to ALC on back of amp, and of course the other would go to ground?

    ALC I have never hooked up before as like you I only ran back about 90 watts, so that is confusing to me yet.
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