replacing 6146A with 6146B

Discussion in '"Boat Anchor" & Classic Equipment' started by AG5LS, Feb 27, 2018.

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  1. N8YX

    N8YX Ham Member QRZ Page

    Insert cursory 'Ogre' line "NERDS!" here... :p
    AC0OB likes this.
  2. AC0OB

    AC0OB Subscriber QRZ Page

    AXN: "You cannot have determined the velocity without knowing the attributes of the CG and SG alignment, distance of the CG to SG, distance of SG to virtual cathode, and distance to plate from the center of the virtual cathode. All affect electron velocity."

    And your calculations show what electron velocities under static and dynamic conditions for simple Tetrodes and "Beam-Forming" Tetrodes? You brought up the topic of electron velocities so I thought you may have some technical information based on tube physics.

    AXN: "There are no specifications in any data sheets that provide velocity measurements under the varying conditions or even static conditions."

    Of course not, you have to know something about vacuum tube and electron physics and you have to take the mathematical expressions and program them into a scientific programming language.

    For the heating calculations, I actually measured tube dimensions to within 0.5mm. Where are your measurements and calculations?

    See post #79 where QAA gave some excellent online references and downloads to which I referenced earlier. I actually have in my possession those texts in hardcover.

    AXN: "Tubes like the 12DK6, 6BZ6, and most other small signal tubes using class A mode will have beam forming plates to keep the stream away from the grid mounting posts --- and no suppressor grid because they don't need them --- the plate never drops near the screen voltage."

    Sorry, Your response here is simply techno-speak fodder.

    AXN: "suggested reading: "Electronic and Radio Engineering" Terman fourth edition. Let me know if you need a copy, it's a classic. I have two left in hard cover."

    I have three editions, which chapter and or page might you be referring to?

    And for the third time: Who were these RCA tube engineers who supposedly gave you this "inside" information?

    Kindest Regards,

    Last edited: Mar 13, 2018
    KM1H likes this.
  3. K9AXN

    K9AXN Ham Member QRZ Page

  4. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    I have provided a link to free downloads of those books to anyone interested in the topic.
  5. AC0OB

    AC0OB Subscriber QRZ Page

    Recommend you re-study and re-read, "Electronic and Radio Engineering," Frederick Emmons Terman (Editor), Chapter 6, starting with Page 169, McGraw-Hill, Fourth Edition, for a good overview of electron emission and the different tube types, particularly Section 6-9 and 6-10 regarding Screen Grid Tetrodes and Beam Tubes, because it appears you have a somewhat distorted view of both the Physics and Architecture of these tubes.

    Again for the fourth time: Who were these RCA tube engineers who supposedly gave you this "inside" information?



    Last edited: Mar 13, 2018
  6. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    I find it difficult to have technical discussions with you. You develop bizarre theories (e.g. your concepts that Heathkit engineers had no idea how to select/design inductors for the SR2000; per your website) and your 2/1 variation claim. You toss in irrelevant trivia, e.g. number of "beams" in the tube. You use odd/non-standard nomenclature/symbols e.g. 2/1 vice 2:1. You constantly move the goal lines or redefine statements you previously made. sigh.

    -I don't believe in conspiracy theories.
    -I don't believe Heathkit used factory hand selected tubes from RCA
    -I don't don't believe there are "secrets specifications" for RCA 6146 family tubes

    The rest of your claims become too muddled and drifting to follow.

    "You asked me..." bill
    AC0OB likes this.
  7. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Let me add... When RCA says that later model 6146's are backwards compatible, keep in mind they cannot account for design decisions and configurations of any particular (or all) radio(s). Yes there are differences between in the 6146 family.

    ****It is always possible for a radio engineer to create a design that operates near the limits of the tube or lacks sufficient adjustment range to compensate for variations or is sensitive/vulnerable to particular conditions.*****

    Adding: The 6146 was a major advancement in power tubes; quite small and built to tight tolerances. It may not be as accepting of radio designs that used older construction methods or circuit concepts, such as poor shielding/block isolation, long component leads, circuitious or long ground leads, as exemplified by 1950 era radios the TBS-50 and Viking II which I am familiar with. The designers of these radios were founded in bread board design practices that was becoming unacceptable in the era. (not that these have direct bearing on the 6146 discussion).

    Last edited: Mar 13, 2018
  8. AC0OB

    AC0OB Subscriber QRZ Page

    I almost forgot about this text by Spangenberg as well, a classic work in terms of the details of vacuum tube construction and theory:

    See Section 10.3, Page 238, regarding tetrodes and Screen Grid Tubes, very enlightening:)

    This Prof. taught vacuum tube theory to most of the engineers for the major tube manufacturers.

    Last edited: Mar 13, 2018
  9. N2EY

    N2EY Ham Member QRZ Page

    It read all these analyses of electron velocity, beam forming plates, etc.


    The real issue is being side-stepped IMHO.

    Here it is:

    RCA came out with the 6146 in 1950/51. It is best described as a bigger version of the 2E26 - even the pinouts are the same. Many problems with earlier tubes were dealt with - the base leads are much shorter than in older tubes, there are three cathode leads to further reduce inductance, there's a GT-type base, internal shielding, etc.

    The 6146 was eagerly accepted by amateurs and commercial users alike. Soon other companies like Sylvania were making them. Variants with different heater voltages appeared, as well as ruggedized and pulse versions. And there were improvements, such as the 6146A with its "dark heater".

    Then came the 6146B, with higher ratings. In many applications, the 6146B could directly replace the earlier types - but not all. This was learned the hard way in some cases.

    The good news is that there's a wealth of information about modifications which permit the use of 6146Bs in rigs designed for 6146/A tubes. In most cases the mods are simple.

    We can argue forever about why mods are sometimes needed - I'll leave that to others. The main point is that they may be needed. And, in a rig that uses two or three tubes in parallel or pushpull, they should be of the same type. Not necessarily "matched pairs", whatever that means, but the same number, and hopefully the same manufacturer and similar vintage.

    We now return you to our regularly-scheduled food fight, already in progress.

    73 de Jim, N2EY
    KE4OH, KX4OM, K9AXN and 1 other person like this.
  10. K9AXN

    K9AXN Ham Member QRZ Page

    Regards Jim

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