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Ameritron AL-572 Dead

Discussion in 'Amateur Radio Amplifiers' started by KA1KA, Apr 26, 2021.

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  1. KA1KA

    KA1KA XML Subscriber QRZ Page

    RR. I'm going to test this later tonight and report back. That plate choke looks pretty simple to solder in. Following some reading on the interwebs prior to asking this question, I've also read that D117 seems to be a common thing to blow on these amps but the symptoms don't exactly match what I have going on.

    Thanks for the wisdom, it's much appreciated.

     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I think the "D117" problem will still allow the amplifier to operate and produce output, but the metering won't work properly (typ. grid current will track plate current, so grid current will read much higher than it really is, etc).

    But I believe if you have no B+ to the tubes and everything else is still okay, you should read a lot of grid current if you drive the amp with RF...just no plate current, and no output power.

    Do you show grid current if you apply drive to the amp (keyed normally, and in OPERATE position) with a carrier signal?

    Edit: Oops, I see you did say that in your initial post. So, you have lots of grid current but no plate current and no output: That wouldn't be a D117 failure. Very likely to be "no high voltage" reaching the tubes.
     
  3. W1QJ

    W1QJ Ham Member QRZ Page

    I would think that before you ship the amp to Mississippi and wait months for repair you can send it to me here in Connecticut. Just a suggestion.
     
    K0UO likes this.
  4. KA1KA

    KA1KA XML Subscriber QRZ Page

    If it comes to that point I will definitely reach out to you. The bummer is the amp is only 3 months old.

     
  5. KA1KA

    KA1KA XML Subscriber QRZ Page

    Yes, thanks for the clarification it does indeed have grid current when operating, proportional to the level of input, but peaking very quickly. Will report back once I can get my DVOM on the plate choke.
     
  6. KA1KA

    KA1KA XML Subscriber QRZ Page

    Well, I never even had to hook a meter up. Once I got in the chassis again and knew where to look thanks to you guys- the problem was obvious. Plate choke and that wire are burned up good. Not sure if that wire that also got melted (labeled HVs) is any special type of wire. Plate choke looks like it screws in from a flathead on top and a bracket on the bottom. Not sure if any soldering is required. Part has been ordered and will attempt this repair on my own. Any hints are much appreciated.
     

    Attached Files:

    K4PDM likes this.
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Looks like the choke needs replacement, but it also looks like the "wire" only has a bit of burned insulation and the wire inside is okay. At least that's what it looks like to me.

    The "wire" may not need replacement at all.
     
    KA1KA likes this.
  8. K2XT

    K2XT Premium Subscriber QRZ Page

    If you go to w8ji.com and find the section where he talks about designing that choke you will find it has a parallel resonance around 8-12 mhz, I forget exactly where. But he shows you how it has tremendous high voltages in parallel resonance. In some cases the hv can jump 2 inches.
    Read it, study it, and understand why it happened on 10 mhz. It is great, great information from the man who knows this stuff.
     
  9. G3YRO

    G3YRO Ham Member QRZ Page

    Did you actually measure the resistance of the Plate Choke with a Multimeter, to see if it was open circuit? (just because it looked burnt doesn't necessarily mean no HT was getting to the valves)

    In my experience with these Amps, the commonest reason for no PA current is the contacts burn out on the cheap relays they use in the negative line. (I've replaced at least of 6 of them now . . . and they're a real pain to get at!)

    Roger G3YRO
     
  10. KA1KA

    KA1KA XML Subscriber QRZ Page

    Update: I soldered in a new plate choke. The amp is back to chugging along as normal. Thanks to all for the wisdom and valuable information. Cheers! Adam
     

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