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Discussion in 'Amateur Radio Amplifiers' started by WD5JOY, Oct 21, 2012.

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  1. W0AAT

    W0AAT XML Subscriber QRZ Page

    How many overdrive things trying to get the last watt out? Solid state will die under conditions like that as will some tubes like the 3cx800. Most failures probably go back to operator error, failure to read the manual, or abuse.
  2. SM0AOM

    SM0AOM Ham Member QRZ Page

    A simple test:

    Look at professional or military land mobile, marine and airborne HF equipment.
    Do you find a tube in recent transmitters?

  3. KH6AQ

    KH6AQ Ham Member QRZ Page

    And by "recent" I suspect you mean 30 years.
  4. HK2LS

    HK2LS Subscriber QRZ Page

    My Alpha will handle a 3:1 SWR - they suggest not using a tuner but letting the amp handle the mismatch. I've run it at up to 2.05:1 (as measured on a LP-100A) and tuning the amp needs to be very precise but the amp just clunks along at 1.5 kw with no problem at all. I'm using my AT2KD not as an antenna switch as I don't need it with the Alpha... 73s..
  5. SM0AOM

    SM0AOM Ham Member QRZ Page

    More or less.

    The major solid-state breakthrough came with the Skanti and S.P. Radio all solid-state shipboard transmitters in the early 80's,
    and somewhat earlier for military users with i.a. the SRT SST400 400 W SS ISB transmitter that started to be delivered in quantity to the Danish and Swedish navies in 1973,
    and with the Rockwell/Collins HF-80 family in the mid-80's.

    Airborne HF went solid-state with the ARINC 719 equipment that was fielded in the late 70's.

    The very high inherent reliablity of solid-state MF/HF equipment has made possible the "land-based maintenance" procedures that are the choice of most ship-owners today in the GMDSS.
    It would have been impractical to use tube-based transmitters and on-board maintenance, as it would have required access to technical personnel during the voyages. Previously, the radio officer had a level of knowledge sufficient to successfully trouble-shoot tube transmitters.

    A typical commercial servo-tuned HF transmitter of late 60's design had a large number of moving parts, and often was critically dependent of the condition of the driver tubes. When they became run-down, the servos often failed to converge or stalled.

    The operational profiles of amateur radio amplifiers are very much different from professional equipment.
    I would estimate that the "duty cycle" averaged over a year seldom exceeds 10%. Taking the long service lives of especially
    oxide cathode tubes into account, it would take at least 10, maybe 20 years for the average amateur to wear out a set of final tubes.
    If this is compared to H24 commercial usage, where it was common to run-down a set of driver and final tubes in about a year (8760 hours).
    it comes as no surprise that commercial users go for solid-state to the maximum extent possible.

    Un-manned remote transmitter sites which have inspection intervals of 6 months for cleaning the air filters and checking the storage batteries and the Diesel backup generators are now quite common. Compare this to the man-power requirement of yesteryear, where only the yearly scheduled overhaul of 5 servo-tuned transmitters used nearly 200 man-hours, not counting any random failures.

    Only by replacing tubed transmitters with solid-state have i.a. Air/Ground HF operators faced with economic realities managed to stay in business.
    The Rockwell/Collins 2,5 kW solid-state transmitters that replaced aging tubed servo-tuned amplifiers at Stockholm Radio Air/Ground in the mid-90's
    paid for themselves in about 3 years simply by the reduction of maintenance staff, replacement tube and energy costs.

  6. KD0CAC

    KD0CAC Ham Member QRZ Page

    KJP to WIK - OUCH


    I'm guessing Steve is just looking for info , not to undermine anyone , but I am just going by my reading Steve's posts here .
    He seems to be always helping with info , my only issue is that many times he forgets we are not all engineers ;)

    Lets see if I get in trouble again .
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    Your argument is strong however I would like to point out the antenna systems those commercial transmitters run into are designed for the frequency / frequencies of operation and their parameters are tightly controlled. Commercial aircraft employ a degree of static / lightning protecction as do shipboard, and fixed installations. Few amateurs can afford the cost, complexity to implement the safeguards commercial installations employ. (not to mention that not all hams own the property they live on.)
    Commercial stations are built to withstand lightning strikes most of the time, the average amateur station won't stand a nearby strike, let alone a direct hit.

    It's likely the commercial transmitters mentioned above would be as reliable in the average ham's installation. Unless that installation is in Southern California, one of the most lightning free places in North America.
  8. N4UP

    N4UP Premium Subscriber QRZ Page

    Granted I have no recent experience with tube amps, but in my first incarnation, in the 60s and 70s, I had several 1000 W ( input ) tube amps and pushed them pretty hard and suffered several plate transformer failures, but never a problem with the tubes. In those days I pushed both the transmitters and the amplifiers to their limits, and whenever I encountered high SWR I simply would not be able to load and tune to full power. So, yes, they tolerated high SWR just fine, but I could never get full power unless the SWR was relatively low. Did not have or seem to need an antenna tuner in those days. And did fine without full power.

    Now in my second incarnation, I have only SS transceivers and SS amps ( THP-1.5KFX ). I haven't even tried to push them very hard, because ( 1 ) they are expensive and I am being cautious and ( 2 ) I am using attic dipoles and running more than 600-700 watts output causes other problems ( like melted baluns and coax failures ). So I drive the amps with 20-40 W and run the amps at 500-600 W and at those levels I have had no problems at all. Averaging 30 QSOs a day for eight months now. Sometimes, in contest mode, changing bands every few minutes. So I am stressing them only with regard to SWR and band/frequency changes. I am not stressing them at or near full power. I do use an external tuner, and keep the SWR below 2:1 at all times. Are these amps reliable? Dunno. So far so good. No problems.

    Of course the THP-1.5KFX has circuits that provide protection from high reflected power, etc. Took me a while to learn the limits of my antennas/SWR to avoid triggering the protection circuits, but once I adjusted my "habits" ( selecting drive power as a function of band and SWR, when to reset the antenna tuner after how much of a frequency change, etc. ) . . . no problems.

    Even when I relocate and have some real antennas, I do not plan to push the SS amps, although I would expect, with better antennas and inherently lower SWR I will run closer to full power at times.
    Last edited: Dec 26, 2012
  9. HK2LS

    HK2LS Subscriber QRZ Page

    My Alpha is designed to handle a 3:1 SWR. It's not a tuner - but rather the amp can handle the higher SWR. My AL-80B could not - so my reply is that it would depend on the specific tube amp.
  10. N2EY

    N2EY Premium Subscriber QRZ Page

    1) Contesters are usually the first ones willing to spend the big bucks for new technology. (Example: What was the first common use of a PC in the hamshack? You guessed it: keep the contest log-and-dupe).

    2) The perceived lack-of-knowledge is is due to two things: First, there's more to know, Second, there's less reason to know it. (In the bad old days the tests and rigs in use required a certain knowledge level. Not so much today).

    The problem is that in the old days we learned the fundamentals on low-power, low-cost rigs, and worked our way up. Few hams do that any more.

    But typical amateur service is, at most, a few hundred hours per year. (Operate 4 hours a day, every day, for a year, on a 50% transmit/receive cycle, and you'll rack up 730 hours) Typical 24/7 commercial service is over 8700 hours per year.

    Yet a lot of hams are running SS amps with success....

    73 de Jim, N2EY
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