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. KM1H

    KM1H Ham Member QRZ Page

    Lou, for those who live and die on SSB and only bother talking to strong stations it makes no difference to them and they keep relying on that stupid little S meter reference as if it applies 100% to all.
    If that part of the hobby is what makes them happy so be it.

    Most of what I work has no S meter reading at all or the atmospheric noise is the only thing that moves the meter.

    I see that Topband has been a bit more active with technical discussions now that Mr Know It All JI is gone.
     
  2. KE7TRP

    KE7TRP Ham Member QRZ Page

    That is complete and total bullshit. Higher plate voltage does not make the amp more efficient. I was bored this morning and ran efficiency P in and P out on 40 meters in CW and SSB and there is virtually no difference. The amp makes less power and way less heat in the lower plate voltage mode. On SSB its even better as you have a lower idle current. I can see on some amps the tank, could function better on a certain voltage as you are not hitting the design target impedance. But on an SB220, its not making a difference.

    heatkit actually touts that you DO NOT need to retune the amp between modes and that you can tune up on CW/tune and switch to SSB with out further tuning as the input and output Circuits will be in tune as the voltage and the current are both swtiched. See Page 4 of the manual.

    You should also know that alot of these AM transmitters do not want to be loaded down to reduce drive. You can get away with some under loading and but typically increases distortion and puts the mod trans at risk of arc over. There is no easy way to lower drive on alot of these rigs. Its best to just switch the amp to CW and reduce the heat and output power on constant modes

    Also see the tune up procedure where they call CW/Tune Low power mode and SSB high power mode and instruct you that you can run Low or high power using that switch. Stop putting BS out on the interwebz.
     
  3. AF6LJ

    AF6LJ Ham Member QRZ Page

    It seems silly to me to run an SB-220 in the CW position these days.

    One reason for running the SB-220 in high power has to do with gettering the tubes. Since the anode contains the gettering material. (both Eimac and the Chinese knock off tubes) rather they are graphite of molybdenum, it stands to reason that running the amplifier in high power is better since the tube anodes need to take on a little color in order to keep the pressure low.

    Besides what the Hell; it's only electricity............:cool:
     
  4. W8JX

    W8JX Ham Member QRZ Page


    You do not have to light them up fully regularly. Cooking them a bit every few months or so if enough.

    The weak link in the tube is its seals and the hotter the average temperature is of envelope the more stress on seals. How much stress is open to debate but minimizing it is not a bad idea.
     
  5. AF6LJ

    AF6LJ Ham Member QRZ Page

    That is true however why not run what you have as long as it is below the legal power limit, especially on SSB.
    There is nothing one is going to over stress.
    The SSB / CW switch is a hold over from the time Input Power needed to be calculated and entered into a logbook. :)
     
  6. W8JX

    W8JX Ham Member QRZ Page


    Unless a 3-500z is properly cooled as designed (with a chimney with pressurized air blowing up thru socket to cool pins and then envelope) you cannot fully exploit tubes design ratings.
     
    AF6LJ likes this.
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    You don't run those tubes at maximum ratings in an SB-220 anyway; with that said the tube cools by radiation
    the critical parts are the tube pin seals which are cooled well enough in an SB-220, there is plenty of air flowing past the pins as long as the amplifier is left with the front elevated. Radial cooling is more effective for the anode seal than the recommended cooling configuration.

    The SB-220 has a lot of faults, tube cooling is the very least.
     
  8. W8JX

    W8JX Ham Member QRZ Page

    If sufficient airflow thru envelope is provided it is not a issue. It is foolish to suggest that amp builder knows more about proper cooling than those that designed tube and proper cooling for it. It costs LESS to build a amp without envelops than with them.
     
  9. AF6LJ

    AF6LJ Ham Member QRZ Page

    Radial air flow in the case of the SB-220 provides cooler air than the air that will be directed to the anode cap by means of a chimney, that air is pre-heated.

    Just a remark;
    Your appeal to authority argument really doesn't work for this case.
    1. The amplifier in question doesn't come close to running those tubes at full rated operating specs.
    2. It has been shown time and time again the base seals and anode seal are well below the maximum allowable tempriture for that tube (200C base, 225C anode)
    3. Besides overdriving the only other way a 3-500Z can be damaged in an SB-220 is to
    a. cover it with a blanket
    b. operate it flat on the desk the tube filament pin sleeves will come unsoldered.
    c. grossly mistune it.

    That about covers it.

    Furthermore;
    The ratings published in the datasheet are for continuous service.

    As I have said before all bets are off when it comes to the Chinese knock offs.

    Can you actually come up with justfication to support the implimentation of the 3-500Z in the SB-220 is improper, other than "the datasheet says otherwise." And actually it doesn't. The air system socket configuration is a recommendation not a design requirement.
    Here is the datasheet link...
    https://www.google.com/url?sa=t&rct...yTV9uYGIxCxjfw&bvm=bv.125596728,d.cGc&cad=rja
     
  10. AF6LJ

    AF6LJ Ham Member QRZ Page

    One more thing, if the way Heath, Swan and others provided cooling in their amplifiers Eimac wouldn't honor the warranty on said tubes.
     

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