No output from Al-811h

Discussion in 'Amateur Radio Amplifiers' started by F4HPX, Jul 21, 2020.

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  1. F4HPX

    F4HPX XML Subscriber QRZ Page

    I have an used and older, I suppose, Al-811H with single T/R relay that suddenly stopped giving any output power.
    in Bypass everything is OK but in operation mode no any output power is metered on my LP-100A.

    I changed btw fuses that were "repaired" by previous owner by the new ones and as 3 of 4 811A were really used I replaced all of them.

    I noticed that the red wire in teflon tube (?) going from the bottom of the white vertical tube with coils between the 811s is going nowhere... looks like broken. Not sure where it is on the schematics.
    Any ideas ?

    Thomas F4HPX /AG7JQ

    Attached Files:

  2. G0JUR

    G0JUR Ham Member QRZ Page

    Looks like the high voltage cable from smoothing capacitors to anode choke.
  3. F4HPX

    F4HPX XML Subscriber QRZ Page

    On some pictures on website W8JI I can see this wire below circuit board but mine is above...
    Have to make sure capacitors are discharged to avoid becoming SK too early before looking below.
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Looks to me like the wire that connects B+ (HV) from the power supply to the plate RF choke lost its connection and needs to be re-soldered.
  5. F4HPX

    F4HPX XML Subscriber QRZ Page

    OK another check to perform...
    I suppose that could explain maybe loss of power?

    If someone has a picture of that part would be great.

    BTW I think the tubes should arced in the past because after watching meters the diode D16 is to be replaced as well - it looks like it will be a pretty complete refit...
  6. F4HPX

    F4HPX XML Subscriber QRZ Page

    well I think found the place to solder according to the video from M0UKD interesting modification
  7. G3YRO

    G3YRO Ham Member QRZ Page

    I actually mounted a small fuse holder on the PCB on a couple of those Amps and connected that red wire to it.

    When the 811s flash over (as they seem to often do in those Amps!) it seems to stop it burning out the Relay (the later amps have two cheap plastic relays, and the contacts burn out really easily)

    Roger G3YRO
  8. F4HPX

    F4HPX XML Subscriber QRZ Page

    Thanks Roger

    I think will do the same in mine.
    I have an SPE 1.3kFA on order but I would like to have this 811H fixed and working again as well.
  9. F4HPX

    F4HPX XML Subscriber QRZ Page

    Resoldered broken cable but problem still unresolved.
    All the tubes are glowing as expected.
    HV reading 1800 V.
    when pressing PTT in OPR position both meters slightly move in right direction and relay clicks
    when in STBY mode I can see exciter power passing through
    When applying RF in OPR position nothing is coming out but both meters move toward simultaneously and proportionally to exciter power ( I suppose D16 problem - ordered already to be replaced soon)
    XMT lights on but no RF out... and amp/tubes absorb all the power.
    T/R Relay issue (the older single model) ?
    Any feedback welcome.
  10. KI8JK

    KI8JK Ham Member QRZ Page

    Did it burn plate choke? Where the wire soldered onto, maybe the choke came unsoldered there.

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