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FL-2100F Continued

Discussion in 'Amateur Radio Amplifiers' started by K6GB, Jul 28, 2018.

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  1. K6GB

    K6GB XML Subscriber QRZ Page

    Put a new pair of tubes in and the amp doesn't seem to load properly, On 80 I'm getting out about 400 watts but the loading is at zero, and I'm not getting a dip. What do I check next?
  2. G3YRO

    G3YRO Ham Member QRZ Page

    If you're not getting a dip, how high is the Plate current (when you have 400 watts output)? If it's very high, hope you are only transmitting in short bursts ! (2 - 3 seconds)

    Is it the same on 160, 40 & 20m?

    If it's bad on all bands, first thing to check is the main RF Choke - are there any signs of burning on it?

    If that looks OK, I would suspect the main coupling capacitor from the anodes to the pi-tank (on top of the RF choke)

    If it's just 80m, you probably don't have the fixed loading padder capacitors in circuit - either because they are faulty (unlikely) or a burnt-out bandswitch (more likely).

    You should be able to inspect the bandswitch visually . . . hard to do a resistance check without disconnecting things.

    Roger G3YRO
  3. K6GB

    K6GB XML Subscriber QRZ Page

    Ok, I'm getting about 300ma on 80 much less on 40 and up, the bandswitch looks ok RF choke clean- no burned or discolored spots. I know which capacitors you mean, since it's open is there a cleaner recommended for the switch? You're referring to c C223, C226, C224, 224 on the plate side and the other 2 on the loading side of the inductor?
  4. G3YRO

    G3YRO Ham Member QRZ Page

    I always use Servisol switch cleaner/lubricant . . . never found it causes any issues, even on Linear Amp band switches.

    If you're only getting 300mA PA current . . . AND not much of a dip, then it sounds like you don't have much drive. (if you had high PA current and not much of a dip, it would be like you had the PA over-loaded, ie not enough capacitance on the Load control . . . which is why I said the Load padders might be faulty or not switched in. But I don't now think that's your problem)

    How much power are you driving the amp with? (for full power output it needs 100 watts drive)

    And you are getting a BIT of a dip, right? Which corresponds with max power output? (ie the PA Tank circuit IS resonating OK)

    With 100 watts drive, and the Load capacitor fully meshed (ie at 0 on the panel markings), you should get a BIG dip in PA current. (ie from nearly full scale down to about half scale) As you then increase the Loading cap a bit at a time, you should gradually get less of a dip, as the power Input (and output) increases.

    Just do make sure when you are doing these Tuning checks, you always just do it in short 2/3 second bursts, if you want your PA Valves to last a long time!

    Roger G3YRO
  5. K6GB

    K6GB XML Subscriber QRZ Page

    100 watts drive, only a hint of a dip on 80 none on the higher bands, I'm going to open it up and look around. I'll take notes, it has had a soft keying board installed, but that shouldn't make any difference, it looked like a very well done job.
  6. K6CLS

    K6CLS Ham Member QRZ Page

    Did it work correctly with the old tubes?

    I've burned a band switch, it had zero conduction, but no visible damage or smell.
  7. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    This is a good suggestion... check the wiring and switch out with your favorite VOM-DVM.
  8. K6GB

    K6GB XML Subscriber QRZ Page

    No, just about the same, guess I have a spare set.
  9. G3YRO

    G3YRO Ham Member QRZ Page

    The things you are saying are contradictory to what I would expect . . .

    With 100 watts of drive, if you're not getting much of a dip that would suggest there's too little load capacitance. BUT your PA current would be very high (and you say it's not)

    And also if there was a problem with the bandswitch or the Anode coupling capacitor, this would cause low output . . . BUT again, the PA Current would be very high.

    So . . . the symptoms are just like low drive . . . and NOT a problem with the Pi-Tank.

    Does the SWR between your rig and the Amp look OK?

    Also, in Tx but with no drive applied, what is the Amp's Standing Current?

    Roger G3YRO
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I know some love the FL-2100s but I've serviced so many of them over the years I'd always recommend an SB-200 instead, if possible.

    Very similar design, but better components and a better design IMO: It (the SB-200) monitored grid current (!), the most important thing to monitor with any kind of tube amplifier.

    I'd always pay more for an SB-200 than any version of an FL-2100.:)

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