Advice with an 811H amp

Discussion in 'Amateur Radio Amplifiers' started by K1OIK, Dec 29, 2017.

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  1. K1OIK

    K1OIK Platinum Subscriber Platinum Subscriber QRZ Page

    1. First look at the video and pay attention to the last click, what is it? I thought it was an arc but there is no snap.

    2. Also the normal dip and load doesn't seem to play out as advancing the load if anything slightly lowers power.
    3. What output should I run on AM?
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If a tube arcs internally, even for milliseconds, it can take out a diode that operates the metering and from that point on, you can ignore the panel metering because it won't be right.

    AL-811H safe carrier power for AM is about 75W (carrier). That's per the guy who designed it.
  3. K1OIK

    K1OIK Platinum Subscriber Platinum Subscriber QRZ Page

    It clicks with these tubes and the previous weak tubes so its not tubes arcing.
    Can I use a variac to the amp to lower the input voltage to get less AM output, right now with my Ranger it is 200 watts (that won't fly long).
  4. KP4SX

    KP4SX Premium Subscriber QRZ Page

  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Lots of things can make a "clicking" noise, including the HV filter capacitors and their equalizing resistors, or a less than perfect connection anywhere in the HV string from the supply to the tube anodes.

    Don't run the amp at 200W carrier power, that will grossly exceed the amp's ratings.

    Don't use a variac, that would reduce both B+ and filament voltage and be damaging.

    Best way with a Ranger as an exciter would be to reduce the Ranger's output via a 6 dB power attenuator.

    Frankly, a Ranger can run at least 50W carrier power output on AM, which with 100% peak modulation is 200W PEP. The AL-811H can run safely at about 350W PEP on AM, so the difference isn't much. Huge difference between plate modulation and a linear amplifier when it comes to AM.

    To run "serious power" on AM with a linear amplifier, a 1500W PEP amplifier is pretty much the way to go and some (with big enough power supplies and cooling systems) can run 375W carrier power on AM. An AL-1500 can do that.
    N2EY, WA7PRC and K1OIK like this.
  6. K1OIK

    K1OIK Platinum Subscriber Platinum Subscriber QRZ Page

    As I watch the video I notice the meter light flicker on the click. But in the shack it certainly doesn't sound like an arc, no snap, no smell, sounds like a big relay engaging but there is no big relay.
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If the meter light flickers, almost for certain it's a HV power supply arc.

    Open it up and carefully check all the filter capacitors and their parallel equalizing/bleeder resistors.

    It can help to operate with the cover off and any HV interlock defeated, then turn the lights out and operate in a completely dark room and look for any evidence of a small arc. They don't need to make any smell or snap, just a "click." In my experience, this is often a filter capacitor.
    K1OIK likes this.
  8. WZ7U

    WZ7U Ham Member QRZ Page

    Don't use your tongue to check for leaks o_O
    KQ9J likes this.
  9. WJ4U

    WJ4U Ham Member QRZ Page

    It's not working right unless you get a 59++ report. :cool:
  10. K2XT

    K2XT Premium Subscriber QRZ Page

    It is a little hard to tell about the click, since you were keying it on and off, and a viewer is not accoustomed to the environment (how loud the snap really is because of room acoustics).
    But I will offer one other possibility - the plate coupling cap. It has happened to me twice with amps. The cap gets leaky, and the B+ voltage arcs to ground through the plate choke across the load capacitor.
    With the other good suggestions you have been offered here Burt, I think you can locate the source by process of elimination. Remove tubes (you substituted others so you might have eliminated a tube as the source already), unsolder b+ to isolate the power supply, unsolder the coupling cap to eliminate anything in the pi network circuit.
    Even within the power supply, you could isolate the filter caps in case it was an arc in the transformer hv winding.
    Good luck with it. I think you are close. And aren't you happy it is not a fancy solid state amp with some exotic problem?
    Oh, one more thing. You might post a short note in the amplifier forum in the technical area that this discussion is taking place. People like Louie, W1QJ hangs out there and he might have ideas.

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