Yaesu FT-991 to Henry 2k

Discussion in 'Amateur Radio Amplifiers' started by AD0AC, Dec 5, 2016.

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  1. AD0AC

    AD0AC Ham Member QRZ Page

    I'm going to be connecting my new Yaesu FT-991 to the Henry 2k in my shack. The Henry uses a 12V T/R relay and the transceiver only needs to ground the center pin of the RCA jack to key the amp. My Kenwoods were able to do this without a problem, but the Yaesu does not appear to use an internal T/R relay for external linear amp keying. The Yaesu manual is less than helpful when describing the connections on the TUNER/LINEAR jack on the back panel of the amp. I'm assuming that if I connect the RCA to the pins for TX GND and GND, it should provide the path to ground to key the amp.

    I ordered a cable on eBay that should arrive today or tomorrow, and my plan is to see which pins the connector is actually soldered to. My assumption is that they connected it to the 13.8V pin and TX GND connector. I don't think it will hurt the T/R relay in the amp, but would it damage the transistor keying in the transceiver? I was thinking that if the transceiver is keying 13.8 volts on transmit, I could just use an external relay with the transceiver keying that relay, which would then close the coil on the Henry and key the amp. Am I getting too complicated with this setup?
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    No, the keying voltage comes from within the amplifier not from the FT-991, so there would be no connection to +13.8Vdc.

    They keying pins are at the TUN/LIN connector, pins 2 & 3. Pin 3 is ground, pin 2 goes to the center post of the Henry's phono jack for keying.

    The FT-991 manual doesn't seem to state the ratings for the internal keying switch. Might pay to just call them and ask.
    AD0AC likes this.
  3. AD0AC

    AD0AC Ham Member QRZ Page

    Thanks Steve, I figured 2 & 3 were the proper pins, so I'm hoping the cable is wired like that. Otherwise, I'll just redo it myself after I call Yaesu to confirm the connection. The new rig works great, but I wish the Yaesu manual was a bit clearer like the Kenwood manual.
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yeah, it's a very l-o-n-g manual that's long on stuff nobody needs to know and short on actual technical information.

    Unforgivable for anyone to create a consumer product with lots of I-O ports and not address specifically the ratings of all pins and connections.

    Just as unforgivable, and most amateur equipment manufacturers are guilty of this (it's not just Yaesu) is to have I-O port connections that can be damaged by overload or short circuits. Resettable, tiny surface mount fuses cost pennies and could protect everything very well. Even your USB ports on your computer use those, in case you short circuit a cable or try to use something that draws excessive current. It's all "behind the scenes" and the user needn't know about them -- but they're there.
    AD0AC likes this.
  5. N6YFM

    N6YFM XML Subscriber QRZ Page

    I have a Henry 2k amp.

    Yaesu transceivers are famous for using a very wimpy tiny transistor for switching the amp keying output.
    The Henry amp uses a standard large 12 volt relay. It draws a little less than 150ma going from
    memory. I also use a Yaesu 3000 transceiver, and don't wish to risk killing the transistor on
    the Yaesu PCB, since it is a common problem and expensive to fix.
    The Yaesu FT-991 keying output "should" be able to handle the 150ma, but I am concerned
    that so many Yaesu owners have lost the output transistor.

    So I use a keying buffer between the transceiver and my Henry 2K amp just for extra safety.
    There are lots of them available, from Harbach Electronics, MFJ, and other sources.
    You can also make one.

    It may not be technically necessary, depending on the rating of the 991 key output line,
    but if you google for problems, plenty of Yaesu users have them :-(
    Better safe than sorry.






  6. AD0AC

    AD0AC Ham Member QRZ Page

    Thanks Neal. I may do that. I left a message at Yaesu and sent an email, so we'll see what they say in a couple of days. I actually replaced the T/R and other relays in the Henry this fall when I was finishing up the repairs that took a better part of three years to complete. The new Potter and Brumfeld relays are rated to draw 100 mA. I may just use the keying line on the Yaesu to key a much smaller relay that will ground the T/R relay in the Henry.
  7. KA8NCR

    KA8NCR Ham Member QRZ Page


    I never interface a Yaesu radio without an opto-coupler.
    KD2ACO likes this.
  8. K6BRN

    K6BRN XML Subscriber QRZ Page


    I don't think a buffer between the Henry 2K and the FT-991 will do any harm. But I've looked at the keying circuit in the FT-991 Technical Supplement (service manual), and it should be able to key the Henry 2K without damage.

    The FT-991 keying circuit (TX GND) uses a reasonably strong 2SD2211 transistor in an open collector configuration to drive its TX GND port. This transistor is rated at 160 VDC C-E, 1.5A continuous, 3A intermittent and 2W dissipation. It is protected against inductive surges by a reverse biased diode and inductor (for RF protection as well). Plenty robust to key a 12 VDC/150 mA relay, unless the Yaesu PWB traces are gossamer thin. I'd guesstimate that this interface is probably safe up to at least 30 VDC and 500 mA with margin - enough to key even the mighty Henry 5K at 26 volts, without damage.

    That said, the FT-991 TX GND interface, like that on the FTDX-3000 and FTDX-1200, can only be used to drive a +VDC keying line to ground. An AC keying voltage or a negative keying voltage (or reversed lines) will destroy the keying transistor, protection diode and possibly even the PWB traces. So do NOT try and directly key an old tube amp, like the SB-200 or similar, that uses a -100 VDC or AC keying line - the Yaesu will go BOOM!

    There are posts on this and other forums that INCORRECTLY state the Yaesu (FTDX-3000, 1200, 991) solid-state TX GND keying interfaces are capable of driving negative and AC keying lines. NOT TRUE! This very bad advice has probably lead to a number of destroyed keying interfaces and blown PWB traces on Yaesu rigs.

    Best Regards,

    Brian - K6BRN
  9. K6BRN

    K6BRN XML Subscriber QRZ Page

    Ummm. Just found yet another post that states the FTDX-3000 TX GND line can handle up to 100 volts AC. IT CAN'T! DO NOT DO THIS OR BOOM!

    Brian - K6BRN
  10. AD0AC

    AD0AC Ham Member QRZ Page

    I received the cable on Friday and hooked it up to a little "buffer" box I built a couple years ago to deal with a 30L-1 I was testing. The radio has no problem keying the little SPST relay from Radio Shack in there, I think it's rated to draw something like 30 mA. I haven't tried using it to key the Henry directly, but BRN's description of the keying circuit gives me more confidence to do so.

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