Collins 30L1 design questions

Discussion in 'Amateur Radio Amplifiers' started by K9AXN, Feb 16, 2018.

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  1. W1QJ

    W1QJ Ham Member QRZ Page

    Glen, very interesting information and I can identify with this. A few years back I got a call from a ham friend of mine who I did some professional work for at his home and while there performing those duties he asked if by chance I could repair his old Swan 350 radio. I said lets have a look. In a few minutes I tracked the problem down to a blown diode in the PS and we took a ride to RS to get one. Once replaced the radio came to life. He never forgot that. This fella was a Phd and was the dean of "outsource education" at the local state college. He called me once and asked me if I would like a job teaching. He needed an instructor to teach "electrical/electronic troubleshooting 101". I would only commit after a read the course syllabus. I did, and accepted the position. I had to teach basic troubleshooting of electrical/electronic equipment. Very entry level stuff but to give a basic understanding. The company felt it was good training for anyone being around such equipment. It was a fun thing.
     
    K9AXN, W1BR and KD2ACO like this.
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page


    It might, but then I've had SX-28s which are much older than the 30L-1 which worked perfectly also. My last NC-300, which is also older than a 30L-1, had zero service in 60 years and was also perfect.

    My first homebrew "high power" rig was designed and built by me in 1967, so it's now 51 years old, using a 4-250A modulated by P-P 811As and is entirely homebrewed using surplus parts and still works exactly as it did in 1967. It's my "AM" rig I use to check into the AM net and the Collins AM net on the west coast. The only thing that ever wore out were the #47 pilot lamps in the meters. The original G.E. "Pyranol" oil-filled caps in the power supply are still there.

    So, to me, stuff lasting a long time isn't much validation of engineering excellence...but may be validation of using "good parts.":p
     
    NL7W likes this.
  3. W1BR

    W1BR Ham Member QRZ Page

    Much like vintage HP test gear--even the electrolytic caps they used rarely fail.
     
  4. KN1M

    KN1M Ham Member QRZ Page

    In regard to education levels in the military, I was in the US Army in 1966-68. In 1967 they dropped the test score requirements for enlistees/draftees to acquire more cannon fodder for Vietnam. Unfortunately for the new men, their Service Numbers began with US67 so they were immediately identifiable. We had a guy in our unit who could only write his name; however, he was very good at his assigned job. How do I know this? I was the Company Clerk. We had all the scoop on people before they even showed up for duty,
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yeah, but could you hear a helicopter coming in ten minutes before it was overhead?:):p
    upload_2018-2-20_9-3-12.jpeg
     
  6. K9AXN

    K9AXN Premium Subscriber QRZ Page

     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Re the W8JI-designed amps, refer back to Post #16 here.

    Tom later admitted he made a big mistake copying what Collins did, and every AL-811H (4 x 811A) amp shipped since Q1 2011 has directly grounded grids. Although I can't confirm this, I understand that's over 22,000 amps shipped with the directly grounded grids and reports after the change indicate a leap in customer satisfaction and reliability.
     
  8. K9AXN

    K9AXN Premium Subscriber QRZ Page




    Of course you can't prove it. There might be an improvement in customer sat and it would be that you now didn't need to replace parts just have a good stock of tubes.

    WB2WIK Provided:
    Important note!
    I suggest removing C32-C35 , removing R19 through R22, and directly grounding the grids with a short heavy lead in the AL811H. Also install two 150-volt to 170-volt gas voltage protectors, one from each filament line at any tube socket to ground at the socket.



    [​IMG]
    This is an important modification to the AL811H. This mod removes the grid resistors and bypass capacitors, and directly grounds the grids.

    In addition two gas voltage clamps, GT1 and GT2, are added. These are 125-150 volt clamps. I have them available for $10 including shipping.

    This mod prevents:

    1.) relay damage

    2.) exciter damage

    3.) grid resistor failure

    This modification improves reliability of the amplifier by directly grounding grids. Amplifiers produced after early in year of 2011 have this modification.

    K9AXN:
    The gas discharge clamps simply prevented tube grid shorts from damaging other components. That change was available for the 30L1 also. in the 30L1, you didn't have to remove the components that provided -5db of IMD improvement and the means to tune the amp at 300 watts which prevents the tube failures resulting from tune up at max power out.

    Grounding the grids did nothing for linearity except make it worse. Those tubes are more likely to fail with the grounded grid configuration --- the clamps simply prevent damage to other components --- take a moment to read the 811A data sheets.

    Regards Jim
     
  9. K9AXN

    K9AXN Premium Subscriber QRZ Page

    I came to believe that, myself (the instability) since with every 30L-1 I've serviced, as soon as I used multiple very short and broad copper straps to ground the grid pins and biased the tubes via their cathodes rather than applying negative voltage to their grids, every trace of instability I ever encountered disappeared.

    K9AXN:
    What circuit did you use to measure the grid current? How did you generate ALC? Also please, a photo of parts placement and schematic of your finished design.

    You serviced many 30L1's and seem unaware that "Phase Tuning" is not part of the 30L1 design but "Automatic Load Control" is. Phase tuning is used to precisely resonate the in and out, and is not used in the 30L1. "Automatic Load Control tuning" however, is used in the 30L1 and is totally different: It is essentially used to protect us from ourselves. You were disappointed with the Automatic Load Control function in the 30L1. Please describe exactly what it does and how you perceive it to be implemented, and what function failed your expectations. I would like the opportunity to work with you to change your mind.


    Regards Jim
     
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I feel no necessity to carry this further. I don't need to change my mind. I never measured grid current, but neither did the 30L-1 and I believe that was a mistake as it's the best way to check tank resonance (much more precise than looking for a plate current dip).

    I never used ALC with a 30L-1. It can handle the 100W output of most modern transceivers.

    No need for further discussion, as it appears you are promoting the "design" rather than the real-life, hands-on functionality. I think the design was weak in several respects, but if you don't, that's fine.

    -30-
     

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