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Is it time for amplifier mfgrs to step back and "rethink"

Discussion in 'Amateur Radio Amplifiers' started by KM5FL, Sep 6, 2011.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I agree, and this is really silly considering what's involved to correct it (in DSP rigs, basically "nothing" except some lines of code).

    Modern Ten Tec rigs all have T-R loops that provide for time sequencing, and you can set the timing via the menu.
     
  2. WB3BEL

    WB3BEL Ham Member QRZ Page

    -30 dBc/tone IMD is -36 dBc/PEP for two tone test. Not many amps today are that good. Probably not a single commercial made amateur amp at its "Rated Power". It's more than 10 dB better than most ham transceivers...

    The T/R switch sequencing issue would be an easy fix. But in many rigs it really is not the timing that is the big flaw. The big flaw is that the internal transceiver TX ALC loop creates transmit power spikes greater than desired while the loop is settling. This is primarily because the people who designed these did not really understand control theory. Some manufacturers have figured this out a long time ago. It's not that hard and does not really add much if anything to cost.
     
  3. NL7W

    NL7W Premium Subscriber QRZ Page

    EXACTLY. I'd like to see a columnar table comparing solid-state amps to tube amps -- columns indicating IMD levels, typical power output, retail sale price, and today's value in dollars. Then, we can have a discussion.

    And yes, solid-state amps are prone to transient voltage issues. Tubes are rugged in this regard.

    SS amps have made serious inroads these last few years from technological and cost standpoints, especially in the less than 1000-Watt level. THP is leading the way here. Yet, the vacuum tube is still king at legal limit, for many reasons.
     
    Last edited: Sep 9, 2011
  4. 4L4AGU

    4L4AGU Ham Member QRZ Page

    Here was noted, that tube amps have PI networks and can tune just anything...
    What prohibits you from installing PI network at solid state PA output?
     
  5. K7JEM

    K7JEM Ham Member QRZ Page

    IF tube amps were so much superior, there would be no demand for SS amps. Each type has its own advantages, and disadvantages.

    How many new tube designs are being introduced, as opposed to SS designs?

    SS has pretty much taken over the broadcast industry, except for very high powered stuff. I remember 20 years ago seeing my first high powered TV SS transmitter. It was 20KW out, on channel 11. Used several dozen modules about the size of a big city phone book. Each one put out around 500 watts, IIRC. Was computer controlled, the screen showed output power. You could go pull a module, hot, and watch the power drop by about 3%. Did not affect the transmission, other than power out. Then you could slide the unit back in (hot), and watch the power return. They were using transistors available in 1990.

    With the newer LDMOS devices it should be possible to produce a 1200 watt amp for under $2000. Someone will do it in the next few years, guaranteed. It would be somewhat silly to produce a new tube design, but there are people out there that would buy them, just as there are people buying tube type audio amps and preamps.

    Joe
     
  6. WB0LSR

    WB0LSR Ham Member QRZ Page

    ^I'm with Joe..

    I mean no offense here, but I'm genuinely curious why it is that so many amateurs in ALL fields seem to honestly believe that they've got things figured out better than the teams of engineers and scientists that are running the game. These are people who are working with the latest tech, examining it over and over and refining it, working in the fields of science, public safety, literally everywhere radio is used outside of the Amateur community? They are working in fields where reliability and ruggedness are often of paramount importance.. Clearly, IMO, in this case any crippling issues with solid-state technology would have given it a bad name.

    The superior IMD performance of transistors at 50V has been mentioned I think, and the only candidates for kW usage that I can think of are 50V devices. The idea of using 12.5V or 28V devices hasn't been raised here, and I don't think that anyone in this discussion would consider them a viable option.
     
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    I don't think any of us are saying tube amps are better than solid state; each does have their benefits.
    Speaking of high power solid state amplifiers.
    Where I use to work back in the eighties we built 1200w and 2400w solid state S-band amplifiers.
    the modules were not hot swappable but the system was hard fault resistant.
    That's a lot of power coming out of waveguide at S band from something that doesn't have a TWT or anything with a filament in it.
    No it was not linear. but did operate over 120MHZ bandwidth at one DB flatness.
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I think the big difference is "hams are cheap" and want to get the most possible bang for the buck. Our stuff doesn't have to be 100.000% reliable, probably 98% is good enough for most; and it surely needn't be "state of the art," if the art is expensive and going back a generation is cheaper.

    There are high powered amateur HF amps on the market for well under $2/Watt (output power), brand new.:eek:
     
    N5WVR likes this.
  9. WB0LSR

    WB0LSR Ham Member QRZ Page

    Yes, but a considerable bit of the arguments in favor of tubes over transistors has to do with the idea that they are not as rugged or reliable. As far as cost goes, the most recent LDMOS stuff destroys that barrier. 1.2kW of ruggedized power for $200 from Digikey? IDK, that's pretty cheap, and that's from a world leader in RF tech.
     
  10. K7JEM

    K7JEM Ham Member QRZ Page

    Interesting video from Digi Key:

    [video=youtube;KZF-FR8b71s]http://www.youtube.com/watch?v=KZF-FR8b71s[/video]
     
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