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. W1QJ

    W1QJ Ham Member QRZ Page

    I discussed the meaning of the CW/SSB switch. Name me one amplifier made after the power rule changed that has one.
  2. W1QJ

    W1QJ Ham Member QRZ Page

    Of course they can, and then some. You won't have to be concerned about the "tubes" (3-500) being a problem in key down mode until you reach a point where the amp is making about 1600 watts key down for a pair. As long as sufficient cooling is provided they can sit there all day making that power.
  3. W1QJ

    W1QJ Ham Member QRZ Page

    Silly huh? I think it is pretty silly to discuss throttling back amplifier power for the sake of running gassy tubes. I would rather think that forums like this is where people come for good advice. My advice would be to get some good tubes, or properly getter gassy ones so they can be put back into full service. And stress on equalizing resistors? You mean bleeder resistors? Properly designed bleeder resistors have a power dissipation of 2X the normal dissipation under use, so no worries there. Idle current dissipation? If you read my post it states that the SSB/CW switch is used to add/delete operating bias voltage based on mode. It is not a good thing to reduce the idle current too far down on SSB mode as Reaston properly pointed out. Nay for the rest.
    AF6LJ likes this.
  4. W8JX

    W8JX Ham Member QRZ Page

    It is for good advise and throtting back plate voltage on suspected gassy tubes and then loading them to heat anode to getter tube is better advise than disabling the ability to lower plate voltage and be more prone to arc over with a gassy tube before you can load it to heat it up and getter it.

    You suggest disabling a feature already built in to amp with the justification being so you can repurpose switch. It is better to leave switch as built and add a switch if you really feel you need a extra switch rather than disabling a design feature.

    To run it pedal to the metal is not always the best way to run a amp unless you like having to repair them more often. I have little doubt that had I run my old Dentron that way last 24+ years rather than with reduced plate voltage and 800+ watts out I would of not only had to repair or rebuild power supply by now and not still be using original tubes either.

    Granted many newer amps do not have a selectable HV switch but if you have a amp with that feature, disabling it is not a enhancement.

    REASTON QRZ Member


    The existing amps with hi/low voltage switches gain nothing of importance by rewiring the amp to allow only to have the availability for the highest plate voltage. If someone wants to use the hi tap, they can now use it without changing anything. The idle current will be correct for the higher plate voltage. You want to lower the idle current by adding a zener. Why? The amp worked fine before without changing any bias voltage. If I were to make a mod it would be to add an electronic bias switch and keep the hi/low switch as is.

    I don't know why you have this obsession / crusade to convince everybody to make wiring changes. The only thing you accomplish with this mod is to take away the choice that owners now have. But there is a real negative in rewiring these amps your way and that is to hammer the power transformer even harder than it already is except you would be doing it all the time. That 450VA HV transformer is drawing 4-5 KVA peak when on the higher tap all the time at full load with your mod. If on the CW tap, the xfmr is drawing about 2-3KVA at full load.

    Why don't you give this wiring change obsession a rest. You seem to be the only person who cares. If someone can't make CW contacts with 650 watts, they should probably improve their antenna and not bother to run 1300 watts of CW. And you don't want to open another can of worms with the idea of loading the amp to a lower power and screw up the whole plate load impedance / pi network parameter design.
    Last edited: Jun 2, 2016
  6. AF6LJ

    AF6LJ Ham Member QRZ Page

    Give up it's not worth it.
    We all know what the intended purpose of the switch was, not to throttle back the plate voltage for a marginal tube. Gassy 3-500Zs were not nearly the problem they are today with the Chinese knock-offs of low to poor quality.
  7. W8JX

    W8JX Ham Member QRZ Page

    Granted it was not intended for gassy tubes but IT CAN be used for them. It is silly to disable or remove this from a existing amp. Some seem to think it is pedal to the metal or not at all.....

    BTW I have a lot of respect for W1QJ's general knowledge on amps. I just disagree on his logic for removing the feature in question from a stock amp
    Last edited: Jun 2, 2016
  8. W1QJ

    W1QJ Ham Member QRZ Page

    I'm actually glad there are guys like Reaston and JX. The more they convince others to baby their amps the easier it is to beat them in the pile ups. Although there isn't anything wrong with having a damn good antenna system, it still is to your advantage to run the extra power when needed. I love it when they think an extra db doesn't mean anything. Keep convincing others of this. I love it.
    AF6LJ likes this.
  9. AF6LJ

    AF6LJ Ham Member QRZ Page

    I only think it is unwise to disable it if one wants to keep the stock appearance of an amplifier with such a feature.

    As far as what power level one uses; I leave that to the person who owns said amplifier, that is a personal choice.

    As a general rule when I run my SB-220 I run it off the high tap.
    The SB-220 power supply was built on the assumption that the SSB duty cycle was 4:1, this was relatively common back in the day and make for a number of decent low cost amplifiers. Even the Drake L-4 power supply isn't any better, or at least if it is not by very much. The real weakness in the SB-220 isn't the power supply; it is the bandswitch and tune cap. Operating the amplifier lightly loaded at full power can have destructive consequences. That subject has been dealt with here well in the past.
  10. AF6LJ

    AF6LJ Ham Member QRZ Page

    I circumvent that simply by engaging in my most loved activities on amateur radio Rag chewing. :) An SB-220 won't cave in if you lean on it once and a while...

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