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Two amps (two 3-500z), different drive input power required

Discussion in 'Amateur Radio Amplifiers' started by K5VV, May 28, 2016.

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  1. AF6LJ

    AF6LJ Ham Member QRZ Page

    My Ex had an SB-220 (I have mentioned this elsewhere) he had a pair of wood blocks the amplifier was placed on. Resting the amplifier on its back panel on the blocks the cover came off and went on with very little effort.
    WA7PRC likes this.
  2. AF6LJ

    AF6LJ Ham Member QRZ Page

    In the Power Grid Tubes manual by Eimac they have air system sockets and chimneys for all the glass tubes. Reading through the manual I can not find any of the glass tubes including the 3-500Z that Require air system components.
    As far as building the kit goes; the manual calls out how to make the connections in the filament circuit in great detail. It completely escapes me that people have trouble reading instructions in simple English, Now I can expect some will have problems reading a datasheet for an electronic component, that is another topic for another time.

    By the way............
    Oscar is doing well.
  3. W8JX

    W8JX Ham Member QRZ Page

    They assume you will use their sockets and chimneys that are designed for them because if they truly were not needed that would not be made. I know I have read somewhere in their data in past that ratings are for tubes using designed cooling methods otherwise tubes are de-rated
  4. AF6LJ

    AF6LJ Ham Member QRZ Page

    You just made my point.
    the SB-220 was designed to run at 2KW PEP DC power input minus the drive power. Even assuming 50% efficiency (and we know it north of 50%) you are still running the tubes at less than full ratings.
  5. KM1H

    KM1H Ham Member QRZ Page

    The original aluminum air sockets were ridiculously expensive and very flow restrictive requiring large capacity centrifugal blowers. Fine for military and broadcast 24/7 operation where noise wasnt an issue.

    Many years later and around the same time they came out with a lower cost air system plastic socket that flowed well they bowed to ham and other commercial amp manufacturers pressure and admitted that an axial fan was OK for ICAS CW/SSB at the 2000W PEP INPUT level when certain conditions were met which mostly concerned tube seals.

    Any claim otherwise is so much drivel and basic PM to keep fans lubed and the amp cleaned is strictly owner responsibility and the details are right in the SB-220 series manuals.
    AF6LJ likes this.
  6. KM1H

    KM1H Ham Member QRZ Page

    The only thing funny is your inability to parse details such as researching the cooling requirements of either of those triodes.
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    I was going to say when I returned from the Post Office....
    The air system sockets are fine for compact design configurations. The Military has a habit of wanting everything as small as possible, believe me I know from working at Loral Corp.
    I have a couple of mil amplifier PA castings out in the garage and you would be a fool not to use the air system sockets that were designed for those applications (VHF 4CX-250 designs that would fit in my shoe). This is not a big deal and I don't understand why the OP is worried about a pair of 3-500s that are running under rated in a kit built amplifier.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I've used 4CX250Bs/7280Ws etc. without air system sockets and through-socket-and-chimney cooling lots of times. Sometimes you can save even more space by doing so. The base of those tubes don't require the cooling, the anode coolers do; so you can "pressurize" only the compartment above the socket, force air into that compartment, and exhaust it out through the anode cooler using an "above the tube" chimney that ducts the heated air outside so it won't be recirculated back in by the blower.

    I've done that, it works well.

    You can also do this without a blower (!) by using two muffin fans in series, up against each other, to increase pressure using inexpensive and quiet axial fans. The tube design is slick in that really only the anode fins need the air flow, the base doesn't.
    AF6LJ likes this.
  9. AF6LJ

    AF6LJ Ham Member QRZ Page

    And this all makes sense the only limiting factor are the seal temperatures.

    it is like the old canard about mounting 866s vertical, you only have to do it if you are not willing to take certain precautions in mind.

    The purpose of a datasheet is to let you know what is possible.
  10. KM1H

    KM1H Ham Member QRZ Page

    As long as you are not using the early 4X150/250 with the glass base

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