TL-922A - no reported plate current!

Discussion in 'Amateur Radio Amplifiers' started by KK6VQK, Aug 19, 2018.

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  1. KK6VQK

    KK6VQK Ham Member QRZ Page

    Hm, so whilst poking at this, I found the input tank circuit components don't match the schematics I've seen for this unit.

    10m/15m/20m match the diagram.
    40m has 471/561 on the input side and 391 on the output.
    80m has pairs of 331 and 121, rather than 331 and 221 like on the schematic.
    160m is ok.

    does this ring true with what people have seen done to this before? (it also looks like the 561 on the 40m side has blown, so I need to at least address the 40m tank.

  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    You don't need a "power meter," just an RMS-reading AC voltmeter.

    Since household current really is a sine wave, it needn't even be a "true RMS" meter, just one calibrated in RMS.

    My Simpson 260-5P can do this and my measurements agree dead-on with the fancy instruments the utility comes out to measure with.:p

    Line voltage here runs 242Vrms in winter and 246Vrms in summer (they boost it up to allow for all the central A/C units running, from about May through October).

    But line drop from service panel to your outlet, through the connectors, and through the power cord of the amplifier plus its internal jumper/terminal board and fuses, can all reduce this under load.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'd be tempted to replace them all with new dipped mica 500V capacitors, and go by the original schematic.

    The caps are cheap enough.

    IMO when they fail, someone overdrove the amp, possibly using a tube-type transceiver delivering >100W output power. I've seen guys use Swans and Drakes and old-gen Yaesus and stuff that can produce 150W+ output to drive these amps and that's not a good thing. Some of those old rigs can produce 200W+ PEP. The amp, to run "full power," only needs 100W.
    KD2ACO, KK6VQK and WA7PRC like this.
  4. KK6VQK

    KK6VQK Ham Member QRZ Page

    hm, ok. It looks like someone did the 10m modification but maybe they didn't align the coils? I'll have to look after I get a mirror to look at the bandswitch.

    How do I move those coils around to align that? I can't see anything obvious for how to move the ferrite cores up/down.
  5. KK6VQK

    KK6VQK Ham Member QRZ Page

    Heh, they're a couple bucks each from mouser/newark. What tolerance should I go for? 1%?
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    5% is fine.
  7. KK6VQK

    KK6VQK Ham Member QRZ Page

  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'd follow it.

    I like amps that have the input tuning variable inductors ("slugs") tunable right through the rear panel, like the AL-80B does. They're even labeled by band. Takes a $1 plastic hex tuning tool to adjust them however you want, and if it takes you more than 60 seconds to tune all of them, you're not paying attention.

    One thing I hate about the SB-220 is they put those same type inductors against the front panel with no access holes for any of them, so you kind of have to take the amplifier apart to access them. Dumb.

    Many of the much-older Henry amps did something pretty smart: They put the tuning networks in plug-in assemblies, accessible from the top once you removed the top outer cover. That way, not only could you easily tune them, but if something failed, you could easily replace them. Smart.
  9. KK6VQK

    KK6VQK Ham Member QRZ Page

    Heh! I'm still trying to figure out how to adjust them. They don't seem to have indents for a plastic tool to turn the ferrite slug with.

    If someone's tuned these up before then I'd love to hear it in a bit more detail. Like, how much power am I putting into the amplifier, what do I do about tuning the plate/load, etc, etc. Thanks!
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    The service manual outlines how. (Except for 11 meters :rolleyes:)

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