Swan 1200-X

Discussion in 'Amateur Radio Amplifiers' started by N8SAN, Jun 28, 2017.

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  1. N8SAN

    N8SAN Ham Member QRZ Page

    Hello everyone! First thank you to all.
    I got the heater re-wired to the proper 6v series on 2 sets of 2. PIECE OF CAKE!
    Plugged in new 6LF6 tubes. And hit the switch....
    Everything came up normal. Heaters on looking good!

    I let it sit idle maybe 10-15min (did some research today and found some people let new tubes sit idle for an hour or so)
    Tuned up the Kenwood, then followed the instructions for the Swan. I have to say the instructions are very simplistic for this tuning compared to the Kenwood Hybrid.
    Tune for max smoke pretty much. Not very "technical" in comparison. But I see this seems very common for PA's of this nature.

    Anyway, unfortunately I now have LESS power out. **insert trombone whaa whaaaaaaa**
    I have a Heathkit HM-2140 measuring power and SWR

    For reference...
    with 8950-
    20m-500
    15m-400
    10m-90 (weird)

    With new 6LF6
    20m-400
    15m-320
    10m-50 (really?!)

    SWR
    20m -1.5
    15m-1.6
    10m-1.5

    So I'm either doing something wrong, or something is hurt in the amp itself. Probably not that far of a stretch.
    Any tips or suggestions where to look would be great.

    Thank you again!
     
  2. W0SNL

    W0SNL Ham Member QRZ Page

    Hmmm. Troubleshooting that won't be as easy as the rewiring was. Not knowing anything about the amp it is hard to even provide a starting point. I assume those SWR readings are into a dummy load? I am normally used to seeing lower SWR readings than that into a dummy load. So that brings up something often overlooked -- the coax jumpers you are using. The number of times bad connector solder jobs and/or even bad coax causes a problem is surprising.

    Not knowing if the amp uses tuned input circuits or not, it still might be helpful to put your SWR meter between the rig and the amp. Knowing the drive wattage and the SWR the amp is presenting to the rig on all the different bands might tell us something.
    -Phil
     
  3. N8SAN

    N8SAN Ham Member QRZ Page

    Phil, thank you for responding.
    Well, I don't have a dummy load....:eek: So that is through an antenna. I know this isn't proper.
    I'm using "DX Engineering 8U DX Series Low-Loss 50-ohm Coax Cable Assemblies"

    I was talking it over with a buddy and I thought about this same thing. I have an MJF portable balun/tuner/wattmeter.
    Right now I don't have enough patch cables to connect Kenwood--> tuner -->amp --> Heathkit meter. I will Thursday.

    I connected the Heathkit first between the Kenwood and Swan.... great thought, SWR off the charts. I have read that the Swan is not a tuned input circuit and people have used tuners in-between, BUT no one has ever mentioned what transmitter they were using. I was, incorrectly thinking if I tuned the Kenwood as normal connected to the Swan that it would tune correctly, obviously I was wrong.
    So I put the MJF in-line and was able to get the SWR from Kenwood to Amp to 1.2:1.
    But I have no way of measuring output from amp until the patch cables arrive.

    This will be an elementary question, but I don't understand something. While the SWR was high, it still made a solid 100watts out. So is it reason to believe that since SWR is a measure of % returned energy, that the amp was never seeing 100watts of drive? Is that accurate thought process? If so, how is that? If the meter sees it why wouldn't the amp?

    Yeah theory! :D:D:D
    Thank you!
    Ryan
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Actual power applied is forward power minus reflected power.

    "100W forward power" doesn't mean much, if SWR is very high and there's 40W reflected...that means an actual 60W of output power.
     
  5. N8SAN

    N8SAN Ham Member QRZ Page

    So I wasn't off really. The meter actually reads what the transmit power is, and you have to derive the actual output power by the SWR reading.
    It was showing probably 4:1.:eek:
    That's 36% loss. No wonder power is down.
    Looks like my cables will be there today.....I'll find out tonight. Hope this helps.

    Running this tuner inline is pretty much the only way to accomplish this, correct?

    -Ryan
     
  6. W0SNL

    W0SNL Ham Member QRZ Page

    In my opinion, you can't troubleshoot amplifier problems without a dummy load. Using a tuner / antenna interacts with the output stage, so if you change one it changes the other. If the problem is in the output stage you will wind up chasing wild geese. The amplifier needs a stable 50 ohm non-reactive load during troubleshooting.
     
    AF6LJ likes this.
  7. N8SAN

    N8SAN Ham Member QRZ Page

    That's totally fair. I just didn't intend on getting an amp (if ever) so I don't have a dummy load capable of that type of power.
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Everybody should have a dummy (load).:)

    For HF, one can be homebrewed; however surplus commercial loads can be such a good deal, I've never bothered to homebrew a kW load. My Bird 1200W load is rated for a kW continuously and is good to 2.5 GHz so it's useful on 16 ham bands if you use the original N connector or a 7/16" DIN; that can be swapped for a UHF SO-239 connector and it's still useful on 12 ham bands. It cost $100 (used/surplus of course) at the local ham swap meet.

    Re your actual subject, I have no idea if input mismatch is really your "problem," or not. If the power dropped substantially when you changed tubes (after heater rewiring), I suspect "something else" may be the problem.
     
  9. N8SAN

    N8SAN Ham Member QRZ Page

    I have one, but I don't have a solid 50ohm impedance, nor can I withstand 1kW. :D
    And I know I should have one...

    That's impressive! Certainly not that cheap on ol eBay.

    I guess it's a question of what is "substantially", I messed with it more last night and squeezed 430-440watts on 20m, didn't check anywhere else. So that's 60-70watts down.
    But being that the mismatch is what it is, I certainly wouldn't call this "consistent data."

    I'll be interested to see tonight what it does with the tuner inline.
     
  10. N8SAN

    N8SAN Ham Member QRZ Page

    Well. I guess I'll have to wait until I can acquire a dummy load.
    Virtually no difference.
    What I DID notice however, is in "tune" it's getting the 430ish watts out. But once I turn to SSB and I talk, I saw over 500watts. I'm used to seeing that the other way.
    Tune gives solid 100% output but when you talk it shows lower.

    I also payed very close attention to the meter on the Swan during the tune up. It states that I should see 100ma cathode voltage (with 8950 tubes) during the 2nd step of tuning, before running up the load. I'm showing maybe 80ma? That's 20% but how would that effect output?

    From the Manual- Paraphrasing.
    2-Turn the 1200x function switch to "tune cw" position. Set the bandswitch to proper band and the PA load to 9'oclock. Turn the mic gain control down on the transmitter and be sure the carrier is balanced out. Key up, the PA will now draw "idle current" of about 100ma.

    So this will be on hold for some time until I get a dummy load.

    Thank you to everyone
    Ryan
     

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