Yeasu FL-2100F schematic and or manual...

Discussion in 'Amateur Radio Amplifiers' started by K5ABB, Nov 4, 2017.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Viewing the photos posted above reminds me why I really didn't like that amp (and haven't had one in many years, like 30+).

    Grids should be directly grounded. Filament transformer should be center tapped with positive bias from a simple zener applied to the center tap to bias the tubes, and large resistance switched in series with that to completely cut them off in standby; relay power should be relay power and serve no other purpose; and those round doorknob-looking caps should be real RF rated capacitors and not stuff from old TV sets (which is what Yaesu used in the ones I've seen).

    I completely reworked WA6NCN's FL-2100 back in about 1989 and this resulted in a more stable amplifier and higher output power on 10m, which was a good band at the time.

    Some really like that amp, but I never did.
    WA7PRC likes this.
  2. G3YRO

    G3YRO Ham Member QRZ Page

    Well I've always thought they are much better engineered than other similar amps, like the SB200, KW1000, etc . . . and certainly better than the cheap Ameritron amps ! They also use really good transformers . . . and electrolytics that seem to go on forever.

    I've also found them to be very reliable, and certainly never had any issues with the bias circuit. It's actually quite clever in its simplicity, and is actually more reliable than the more complex system used in the FL2100Z version.

    My own FL2000B (which is the same as an FL2100, but in a different case) worked great for 40 years, with no electrolytics or any other capacitor or component failures! (I sold it recently, as I got a TL-922)

    Anyway . . . coming back to the OP's problem . . . does this oscillation occur on EVERY band?

    Are the valves cut off OK on Receive? (ie no standing current?)

    On receive, of course there is no proper load across the output of the pi-tank, which may lead to oscillation if the valves are not cut off.

    It may be that with the Z bias arrangement in your particular amp that a component has failed, and they're not cut off very well. (as I say, the Z bias circuit is prone to failure, whereas the original simple circuit never goes wrong!)

    Roger G3YRO
    N8VIL likes this.
  3. K5ABB

    K5ABB XML Subscriber QRZ Page

    Thanks for your reply Roger... Yes, the oscillations seem to occur on every band, and they are tank circuit dependent in as much as I can move the oscillation signal around the band by moving the tuning capacitor thereby changing the resonant frequency of the tank circuit. I can watch all of this on the band scope.

    If by standing current, you are referring to plate current, there is a consistent plate current of 40mA or so at all times in receive mode, which increases to approximately 300mA when keyed to transmit depending upon tuning. I think this is typical for this amp, but I'm not dead certain on that. It has no means to measure the grid current.

    I'm going to pull the bottom panel so that hopefully I can measure the grid bias voltage and current under operating conditions... Does this seem like a good next step to you?

    Also FWIW, the amp seems less prone to oscillate when it's well and properly warmed up, i.e. after an hour of operating.


  4. G0JUR

    G0JUR Ham Member QRZ Page

    on receive the plate current should be zero, looks like you got a shorted ceramic cap somewhere
  5. G3YRO

    G3YRO Ham Member QRZ Page

    That is what is causing your problem !

    The standing current should be ZERO on receive . . .

    When keyed to Transmit (but with no actual Drive) the standing current should be around 100mA (0.1 A)

    You obviously have a fault in your Bias circuitry - as I said before, the circuit used in the Z series (which your Amp seems to have) often fails.

    So check all the components on that board.

    Roger G3YRO
  6. G3YRO

    G3YRO Ham Member QRZ Page

    I meant to add that you should be able to find the fault using an ohm-meter . . . ie without turning the unit on.

    Check that the relay on that Bias board is OK (both the coil and the contacts) . . . check that none of the diodes have failed . . . that the capacitors aren't short circuit . . . and the resistors are the correct values.

    Roger G3YRO
  7. K5ABB

    K5ABB XML Subscriber QRZ Page

    Ok, let me see if I'm understanding what you're saying correctly.....

    If there is plate current of any kind, it indicates the the tube is energized i.e.. there is current flow effectively from the filament (with no cathode in a 572B) to the anode. You're saying that if the grid were properly biased (having a sufficiently high negative voltage applied to it) there would be no current flow possible in the tube as the grid bias would shut it down.

    Therefore, there appears to be a fault in the grid bias circuit causing it to apply inadequate voltage to the grid to properly shut the tube down while in receive mode (hence the relay to the PTT or keying circuit which applies the shut-down bias to the tubes grid only when the amp is in receive mode).

    The solution would then be to inspect the bias circuit to find out why the proper voltage is not being sent to the grids.

    Am I understanding this correctly?

    If I am, then would I not first want to test the bias circuit to see what voltage is being applied to the grids before I start going over the gnarly tight little biasing board looking for the offending component(s), or does the presence of a plate current in and of itself provide enough evidence of a fault in this circuitry? Also, can you tell me what level of bias I would expect and need to see for the proper operation of these 572's?

    Thanks, just want to make sure I'm understanding this correctly. I appreciate the schooling
  8. WA7PRC

    WA7PRC Ham Member QRZ Page

    The PM I sent yesterday explains what is going on. :)
    Bryan WA7PRC
  9. G3YRO

    G3YRO Ham Member QRZ Page

    Yes you are !

    But to be honest, I have no idea exactly what the bias voltages would be . . .

    However - there's little point in measuring it. The bottom line is that there IS a fault in the bias circuit - or else you would have NO PA current on receive and only 100mA on Transmit !

    So you might as well start looking for the faulty component on that Bias Board. (which as I say, you can just do with an ohmeter with the Amp turned off.

    Might be worth also checking the 33 ohm resistors going directly to the grids . . . but these very rarely fail.

    As I've said before, it's shame you don't have the normal FL2100 bias/relay circuitry - it's much simpler, and very rarely goes wrong !

    Roger G3YRO
    Last edited: Nov 9, 2017
  10. N8VIL

    N8VIL Ham Member QRZ Page

    If you have the bias circuit like the one in the FL-2100z the bias voltage measured at r201 and r202 (the 33ohm resistors in the picture in my earlier post) in standby should be around -50 volts. If the bias circuit does not have the tripler or doubler then should be around -18 volts.
    Just curious if your circuit board looks like this schematic for the bias board in the 2100z. If it has a relay, it may be possible the relay contacts are stuck not allowing it to switch back to standby cutoff bias.


    WA7PRC likes this.

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