2700V (plate voltage) for AL-80B?

Discussion in 'Amateur Radio Amplifiers' started by KB7QPS, Aug 7, 2016.

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  1. KB7QPS

    KB7QPS Ham Member QRZ Page

    I just received my newest purchase, a used AL-80B in excellent condition. First time ever messing with an amp.

    Turning it on and following the first few tuning steps, I notice that the meter is showing about 2700V to 2750V instead of 3100V that the manual says that I should be doing. I'm assuming (reasonably confident but have not verified) that the jumper is at the factory default of 125V and I measured my line voltage around 117.5V.

    I'm wondering if the 2700V is an issue, and whether I should move to the 115V tap.
  2. KB7QPS

    KB7QPS Ham Member QRZ Page

    Update: The jumpers are indeed set at the factory configuration. I tested out with a 120V power source (Honda generator) and got about 2800V.
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    It looks like that is the Max / Highest Voltage tap.

    So if it was set for 115, It would be over the Max voltage.

    I am sure it would work fine. The voltage drop on the power line comes into play too.

    It may be best not to mess with it.

    Have Fun.
    Last edited: Aug 7, 2016
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'd leave it alone.

    The amp is slightly easier to drive and produces slightly more output at 3100V, but the difference is very small and you probably would never notice it.

    If you re-tap for lower primary voltage, you run the risk of possible excessive filament voltage which will age the tube faster, requiring earlier replacement.
    KA9JLM likes this.
  5. N3DT

    N3DT Ham Member QRZ Page

    Yes, if you're up to measuring the filament voltage, I'd do that first before setting the HV higher. Mine sits at 3100 in idle, but the filament is slightly high, I need to lower it one tap. Remember you will get E drop during key down. I have everything to move to 240V but have not done so yet. I can still get 800W out most bands but usually run about 750. That's measured with my LP100A. I find the power meter on the amp a bit erratic, but it's close enough. My amp is off a dedicated 4 wire #10 wire from the panel, but it's also about 90' long so it will be easy to switch to 240.
  6. VE1IC

    VE1IC Ham Member QRZ Page

    I'd leave it where it is. Once you pump out already 800W or 1KW, 50W or even a 100W more won't matter at the other end. Also your line voltage fluctuates. It may be right now 117.5 V AC, but at a different time of day, month and or year, it is going to change.
  7. WB1E

    WB1E Ham Member QRZ Page

    As the last 3 posters say, the filament voltage is most important. For me, I'd feel good at minus 10% and not going over the rated level. Somewhere in that range. If you do check that, remember safety is only invented when you need it. Don't leave the test leads in your lap. I use clip leads always & monitor the HV well after the circuit has been de-energized before I put my hands back in there. If you don't feel comfortable, find someone else who has experience. Actually a very common standard procedure for an amp tech ham who knows about this stuff.

    Summertime line voltages are a little low where I am. 118Vac. In the winter, 125Vac is typical.
    Please tell us of your final outcome when you're ready!

  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    IMO, no reason to measure filament voltage at all. The AL-80B is well designed and the transformer is perfect for the job.

    If B+ is in the 2700-3100V range (idling), filament voltage will be fine.

    Your line voltage varies exactly inversely to what mine does! Mine is always highest in the hottest summer months and right now is about 127Vrms. During the winter it runs more like 120Vrms. The utility provider is obviously "cranking it up" for the summer as the consumer load currents are much higher when everyone runs their air conditioning.:p
  9. KA9JLM

    KA9JLM Ham Member QRZ Page

    With most new houses being all electric, The voltage gets jacked all over the place.

    The main fuse blows on Thanksgiving day.
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    We don't have any fuses, but do have a 200A service panel and 200A "MAIN" breakers.

    They've never popped.

    Our line voltage doesn't change much at all if we use our electric double oven (40A @ 240V which all four elements going) and A/C (40A @ 240V when it's running), compared with them both being off. Actually, at any given 120V outlet, the change is <0.5V from "we're using a whole ton of power" to "we're hardly using any.":)

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