Which Transformer for homebrew GS-31B

Discussion in 'Amateur Radio Amplifiers' started by K5JCT, Dec 25, 2011.

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  1. K5JCT

    K5JCT Ham Member QRZ Page

    I'm gathering parts to build a 1000-1200 watt amp with a GS-31b tube. I am ready to order a transformer. I like the availability and cost of the Ameritron tranformers. I have looked at the AL-80b and AL-572 transformers. Its hard to tell by the manuals but the AL-80b one has higher voltage but less current rating. The AL-572 has a higher current rating but less voltage. The AL-80b is rated to 1000watts and the AL-572 1300 watts. Yet, the AL-80B transformer is a few pounds heavier.

    So, will the AL-80B transformer handle the extra power out? Is the amp just limited by the 3-500z? I know the AL80b transformer would be a little heavier because it likely has more windings, but 5 pounds difference. I'm sure that either one would suit my project just fine, I just want to fit the best one.

    AL-80B 2700vdc @ 0.6 amps 26lbs
    AL-572 2500vdc @ 0.7 amps 21lbs
  2. KO6WB

    KO6WB Premium Subscriber QRZ Page

    From the specification I have read the GS-31b tube will work better at a higher plate voltage. There are some that use 3KV. If you are not planning on running more than 1KW with the GS-31b then the transformer for the AL-80B would be a good choice. At higher power output levels this transformer is not quite up to the task. The transformer for the AL-572 is probably too low in voltage to get full power out of a GS-31b. I could be wrong. It would be better if you could find a transformer that would get you the 3KV at about .6 to .8 amps. That would be ideal.
    Hope this helps
  3. K9FV

    K9FV Ham Member QRZ Page

    That is my understanding about the GS35b tube -and thr GS31b also, they like at least 3kv, better if that is loaded. I would like to try something in the range of 3500vdc and see how that works...

  4. WA7PRC

    WA7PRC Ham Member QRZ Page

    Efficiency in class AB will likely be right around 55%, give or take. You need ≥ 2180W from your power supply. You're not there with those xfmrs. To get 1200W PO with 1750W of DC (2500V @ 700mA), efficiency needs to be > 68% which ain't gonna happen in class AB. I've heard these tubes like higher HV. If I ever get it finished, my GS-35b will run at ≈ 3300 to 4000V, depending on the xfmr secondary tap (fullwave doubler). I decided to rewind my HV xfmr. The 18 AWG secondary should give me around 1.5A current out of the doubler. IP will be about half that.
    KJ4ZTC likes this.
  5. N3JBH

    N3JBH Ham Member QRZ Page

    I would look at a transformer for one of Ameritron legal limit amp's ( AL-82.1200, 1500) Models
  6. K9FV

    K9FV Ham Member QRZ Page

    Problem with the Al-82class transformer they will handle ll over legal limit while the GS31b tube is normally considered a KW class tube. With the AL-82 transformer a GS35b tubewould be just right.

    Both tubes do like the higher voltages, from my reading anyway.

    73de ken
  7. WA7PRC

    WA7PRC Ham Member QRZ Page

    Tube ratings aside, the AL-82, AL-1200, and AL-1500 use the 404-1418-1D xfmr (2570V @ 800mA). With a capacitor-input filter, this will produce 3634V (no load). Cost = $400 plus shipping... another reason I rewound what I already had. My total investment is around $100 or so.
  8. K5JCT

    K5JCT Ham Member QRZ Page

    I see designs on the web using @2500 volts under load at 1200 volts with a GS-31b. Does anyone have both an AL-572 and an AL-80B? I would be interested in a direct comparison of the transformers. If not I'm going to go with the AL-572 transformer. It comes from a 1300 watt PA. and is cheaper.

    Thanks for the replys, I wish I could afford something larger like 3000 volts at 1.5 amps. I actually looked at the bigger Ameritron transformers. They are really not priced all that high for what you get. But it puts my project over budget.
  9. K9FV

    K9FV Ham Member QRZ Page

    Oh, so you are like, money is the driving constraint of a project? I would lovett have used the AL-82 transformer in my amp project, but $400 was almost my total budget for the amp. That is why I used the GS31b tube.

    Anyone know the cost of the al80 transformer? If the cost of the transformer is the same, I think the little extra voltage of the al80 transformer would best........... I think.

    Good luck and keep us updated on the project.

    73 de Ken H
  10. K5JCT

    K5JCT Ham Member QRZ Page

    406-1109-2C $180 plus shipping from Ameritron

    The little extra voltage would be nice, but will it handle the extra current?
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