Grounding the Grids vs. Cap/RFC Grounding

Discussion in 'Amateur Radio Amplifiers' started by W4LAC, Jun 13, 2019.

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  1. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    There have been countless pages of Zed Threads written about problems fitting newer tubes into classic amps. Some of the problems are solvable (or tamped down to 'workable' situations).

    I'm pretty sure that someone designing a new RF linear amp around 811's would be accused of 'not dealing with a full deck" for the reasons you are eloquently hashing out here.

    IMO at least, the 3-500 seems to be about the best 'bang for the buck' if someone wants to use current production valves for amateur use.

    I went through my whole tube stash and cannot find the 811A's I had to share a picture of the grid wiring. I must have given them away some time ago.
     
    Last edited: Jul 13, 2019
  2. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    -One thing "we" cannot know is what requirements and limitations Ameritron placed for the original AL811 design.
    -We also cannot know what advice Ameritron rejected from Tom.
    -We cannot know what production changes he recommended but they would not implement.
    -We do know they went many years before coughing up the money for a redesign to the AL811A.

    Tom has mentioned in past discussions that the AL811 series was intended as a bottom line inexpensive amplifier, and it is probably not a surprise that it may not have had the most expensive circuit design. Extra components add cost, after all. Nonetheless, the series has had a long production run and has served many thousands of amateurs satisfactorily.

    Despite those who delight in casting aspersions on Tom's electrical abilities, he has designed many successful products for Ameritron/MFJ including the MFJ 1025/1016 noise cancelers, and DXE's NCC-1 and NCC-2 noise cancellers/antenna phasers.

    BTW, Tom did steal the concept of the resistor and capacitor [as well as the use of solder] for use in his designs and has never credited anyone! For shame. Ahem.

    [Edit] Regarding "theft" of ideas and credit; If you didnt' patent an idea, you don't "own" it, and there is no theft. Advice: Be careful patting yourself on the back for intellectual brilliance that you don't throw out your elbow. ;)
     
    Last edited: Jul 13, 2019
    W1QJ, K9AXN and KD2ACO like this.
  3. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    p.s. Anyone care to list the number and models of amateur radio products they personally designed that are in current production? Anyone?

    Maybe 'Ole Tom isn't such a bad engineer after all. ;)
     
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  4. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    I'm hoping that Jeremy can run some simulations with that suppressor sometime. I'm wondering if using that device compensates for directly grounding a 3-500's grid... or makes the situation worse. :eek::oops:
     
    Last edited: Jul 13, 2019
  5. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    My tongue in cheek comment was not about a neutralizing circuit, but about the basic components. It was a joke. shrug.
     
  6. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    I was wondering about this device (or the single version of it in my AL-80B) and what a simulation would show.

    [​IMG]

    https://www.w8ji.com/images/Amplifier/AL811H/AL811H-parasitic-top.jpg


    Yeah... that resistor and capacitor! :p

    Yes, your joke flew over my coo-coo's nest.
     
    Last edited: Jul 13, 2019
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  7. G0HZU

    G0HZU QRZ Member

    I had a quick search and the Al80B looks to be another Ameritron amplifier. The AL80B manual/schematic on their website shows a regular RL suppressor so I think this may be another case where the manual is out of date.

    Do you know the circuit values for your AL80B suppressor? Are they the same as for the AL811H at 100pF x2 and 100R and 180nH?

    What were the original suppressor values for the basic RL suppressor in the AL80B manual/schematic? I can't find these values in the manual anywhere.
     
    Last edited: Jul 13, 2019
  8. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Ameritron is famous for its schematics. One Zed pastime is drawing complete as-builts for their stuff.

    I’ll check it out when I get a chance. Thanks for looking into this. I know there are at least a few of us here that are interested in seeing a model of this amp.
     
  9. KM1H

    KM1H Ham Member QRZ Page

    That design goes to the 80's to counter the L in those 3W MOX resistors and I made them for 572B's in the SB-200, Clipperton L and others when quality carbon comps became expensive and often special order.. Ole Toms caps are 91 pf and my earlier version was 100pf, so even a patent wouldnt have helped stop the copycat. That PC board setup aint cheap.

    Modern Ohmite OY resistors are fine without caps even at 6M.

    I love it when some of the trolls are so quick to give a LIKE to a rather poor answer since it is obvious they do not know any better.

    Carl
     
  10. KM1H

    KM1H Ham Member QRZ Page

    Any competent company has a design team to be sure a product released to production is properly vetted. The lone wolf with a huge ego gets a big bite in the ass in this case and kicked out the door.
    So much for your Like troll.

    Do you really think Ole Tom was 100% responsible for all the MFJ stuff? The one that was his, the MFJ 259B had so many bugs and mods it might have set a record. The 1025/1026 was a little better and now he claims it doesnt work well in order to justify the stupid cost of the NCC's.
    I find my 1026 to do an excellent job after a few simple mods.

    He and DXE are so paranoid many schematic/parts lists are not released to stop at home evaluations and repairs which were often for the NCC-1. Ford was faster on turn arounds:rolleyes:
     

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