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Another Faulty Ameritron AL-11H

Discussion in 'Amateur Radio Amplifiers' started by G3YRO, Aug 5, 2017.

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  1. KA9JLM

    KA9JLM Ham Member QRZ Page

    One transistor powers the other. The schematic fails to connect the dots.

    Have Fun.
  2. G3YRO

    G3YRO Ham Member QRZ Page

    I realise that !

    But the first transistor drives the first relay, and the second transistor drives the second relay, via the first transistor . . . why bother with the second transistor?!

    Roger G3YRO
    AF6LJ likes this.
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    It is a AND gate. Can I say "If you will", Or is that to old school ?

    If they did not do it that way, You would have nothing to fix. o_O
    Last edited: Aug 8, 2017
  4. W1QJ

    W1QJ Ham Member QRZ Page

    Roger, the keying circuit is the way it is timing purposes. Trust me, it's important that the timing is accurate for that amp!
    AF6LJ likes this.
  5. G3YRO

    G3YRO Ham Member QRZ Page

    Ah I see . . . I didn't consider that.

    I wondered why they used two separate relays . . . so with the time constant the top one hangs on slightly longer than the bottom one. Presumably so that the Output is still connected to the Load until AFTER the input drive is removed and the Valves are turned off . . .

    Thanks for pointing that out !

    Roger G3YRO
    AF6LJ likes this.
  6. G3YRO

    G3YRO Ham Member QRZ Page

    Well I've fitted the new Relay . . . and it works fine !

    I also fitted a 1 amp fuse in the HT+ supply . . .

    It's quite easy to fit a 20mm fuseholder like this on the Power Supply PCB, using one of the existing mounting screws.

    So the AL-811H is all back together and ready to take back to the owner!

    Hopefully the things I've discovered about these Amps (mainly from W1QJ) while fixing these two different units will be useful to someone else!

    Roger G3YRO
    Last edited: Aug 10, 2017
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    I hope you didn't do what I think you said you did.
    You put a plain 1A fuse in a 1500V B+ line???
  8. G3YRO

    G3YRO Ham Member QRZ Page

    Yes . . . why not?

    A lot of Amps fit them . . . hopefully it will save more destruction if the Valves arc over.

    Roger G3YRO
  9. AF6LJ

    AF6LJ Ham Member QRZ Page

    Not the high voltage side they don't.
    I guess you have never seen when you take a regular glass or ceramic fuse and exceed the current rating and have that fuse blow. The arc will cause the glass fuse to explode and there may be a fire.
    The Ceramic fuse packed with sand will arc also and you will have the same result unless the fuse is rated for the voltage.

    Don't do that, there is not only very bad engineering practice but Hammy Hambone wouldn't even do it.
  10. G3YRO

    G3YRO Ham Member QRZ Page

    Well even if it does, surely that's better than all the damage caused inside the Amp by an arcing Valve?!

    I know very few Amps fit them originally . . . but a lot of people suggest fitting one as an aftermarket mod.

    I would appreciate it could be a problem if this was 25kV . . . but at 1800V I wouldn't have thought it was an issue.

    Roger G3YRO

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