[AMRadio] Source Broadcast Xmtrs

[Larry D. Barr]

Bravo, Rob. Well put.

PS: "tirade" was the first word that came to my mind too.

On 06/12/2011 09:58 AM, Rob Atkinson wrote:
> Hi Ron,
>
> First, "tirade" may have been a bit of an exaggeration, sorry about that.
>
> Those of use who have been around on ham AM on-line forums of one sort
> or another can probably tell you that any time someone starts out by
> writing some variation on:
>
> "I am a professional broadcaster," or, "I am a chief engineer," of "X
> years experience," we all know we are about to be lectured to by
> someone who knows less then half what we do about ham AM but by virtue
> of his career experience, thinks he has a thing or two, to teach us,
> if we will just sit at his feet in silent awe.   The same is true in
> other cases like hams who go off and get a flex radio (like seeing
> Paris for the first time), then come back and tell us poor hayseeds
> that we should junk our boatanchors and move to the city (but when
> asked how they repair their flex radio when it breaks they never seem
> to have an answer).  Don't get me wrong, it's not that broadcasters
> have nothing to teach anyone, it's that broadcast AM and ham AM have
> some differences.   For one thing, any occupation a guy has to do all
> day to earn a living is going to result in an attitude shift about
> that activity.   To earn a living, I spend all day doing things with
> computers.  So if someone says to me, "I like to tinker with computers
> and software in my free time," I just cannot get away from that person
> fast enough.   A few years ago a friend of mine told me the CE of a
> local class 1-A property (now retired) said to him, What kind of
> whacko wants to see our transmitter site?   Well, I wanted to see it
> and would have thought it a really cool thing to see, but I understood
> where he was coming from, since he had to be there any time day or
> night whether he wanted to or not, in order to earn a living.
>
> So, a professional might wonder, what kind of whacko _wants_ to put up
> with a vintage vacuum tube broadcast rig?  They are big.  Hot.  Very
> heavy.  They use a lot of power and are inefficient compared to a
> solid state rig.  They break down and are unreliable compared to s.s.
> They are also usually dirty because their operating environments
> (often an unattended shed with mice running around) are dirty.   To
> someone who had to keep one of these beasts on the air, and who
> offered up burnt offerings of praise the day his station went solid
> state, the idea of anyone voluntarily wanting to operate one, is
> incomprehensible.
>
> For full disclosure, I run a ricebox driving a linear amp.  And I do
> not have a home that could accommodate an old broadcast rig without
> major remodeling.  But, if I had a basement with a big door opening to
> the outside with a concrete ramp to the driveway, I'd be actively
> looking for a broadcast rig or three right now.  Why?
>
> Well for one thing, no one is making any money running a ham AM
> station.   We're not trying to squeeze every dime we can by making
> sure everything is always running, never down, with no more then 10%
> of the power company's product going up in heat.  The point is not
> profit but pleasure and fun.
> If you understand and appreciate vacuum tube technology, anything with
> vacuum tubes is a beautiful thing, but the sight of the PA and
> modulator tubes in a transmitter showing color through a window is
> lovely.  The old rigs themselves were often works of art, sort of like
> cars from the 40s and 50s--lots of chrome and glass, real jewels.
> The cabinet size and build quality (continuous duty) is simply not
> found in ham gear, even vintage ham gear (no vintage ham AM rig was
> ever made with a modulation reactor as far as I know) and having one
> of these rigs cleanly and quietly putting out a solid 300 - 400 watts
> with a huge audio power reserve (no running out of mod power with
> these rigs) and knowing it could do that with essentially no time
> limit is a thing that is exciting to just about any ham AMer.   Then
> there is the restoration challenge--to you perhaps a PITA but to some
> hams, a labor of love, like restoring a junk 55 Chevy.   And if it
> does break--it can be fixed.  You may be able to repair your ricebox,
> but I have doubts about my ability to repair mine.   I think I can
> generalize by saying that we want to be able to fix the gear we
> have--and that that is one of the characteristics of a complete ham.
> Throwaway plastic radios may be okay for consumer electronics users,
> and hot switching plug-in RF modules that can be pulled out from a
> DX50 and sent out for repair may be okay these days for broadcasters,
> but at some level that doesn't cut it for us.
>
> Sure, I could probably go along with my ricebox (modified by the way
> because stock, it sounds like a traffic information station) and pair
> 3-500zg running 300 watts but the setup is at once boring and a pain
> in the neck.  It's boring because once you figure out how to modify
> the amp to handle long AM transmissions at some decent carrier power,
> the challenge is similar to running a CB rig with a "foot warmer" (or
> whatever they call linear amps now).  But it's a pain because at least
> in my case, I have to always fiddle with the drive level, Z between
> the exciter and amp input, and the amp's loading depending on what
> band I'm on.   Don't you think it would be a lot easier to dip and
> load a class C PA and modulate it?
>
>
>>>    First I was a HAM wannabee when AM was king and the heterodynes were
>>> both hideous and everywhere.
> There are a few simple solutions to that today:  Firstly, we tend to
> spread out more most of the time.  Secondly, it's possible to work up
> a filter and wire it so it can be switched into the IF strip on a
> vintage receiver.  Mouser sells Murata ceramic filters that can be
> used for this.  I put together a 6 KHz ceramic filter circuit using
> one for my 75A-3 because I'm too cheap to pay the big bucks for a
> mechanical filter.  Also, it is not as if everyone transmits 5 or 10
> KHz of audio all the time.   Sure 5 or 6 KHz sounds great.  But every
> ham I know of with that kind of frequency response capability also has
> some kind of low pass filter arrangement to narrow his bandwidth when
> necessary (usually at night on some bands like 75 meters).
>
>>>    Secondly the "big iron" that everyone covets limits the fidelity in ways
>>> that a rice box followed
>>> by a one kW linear amplifier doesn't.
> It depends on the ricebox and whether or not it is run stock.  Also,
> if your amplifier is limited to 1 KW, it is really not adequate for AM
> (in my opinion).
>
>
>>>    Thirdly, USA HAMS are limited to 375 Watts unmodulated carrier, (1.5 kW
>>> P-P) a one kW AM
> Oh boy, the mythical 375 watt power limit again.   How do we measure
> this 375 watts?   What if my Bird 43 says 378 watts but I can only get
> to 80% positive and neg.?  Will I get a ONV from FCC?   Yikes.   Sorry
> for the sarcasm, but the stupidity of the ludicrous imaginary 375 watt
> power limit makes it hard to address with any seriousness.
>
>>> transmitter can produce one thousand Watts of unmodulated carrier.  (so
>>> you need to cut it back)
> What if you want to run it as one hell of a CW or RTTY rig?   : )
> Come to think of it, I'm a little surprised SSTV ops aren't running
> around buying up old bc rigs so they can spend hours on end sending
> photos at 1 KW with no worries like they'd have with their little
> table top amps.
>
>
>>> * everyone disappeared when SSB took over (what ever that is) as did the
>>> heterodynes when I got a BFO
>>>    Early commercial and locally built AM transmitters were often a low
>>> power modulated transmitter**
>>> followed by a linear amplifier
>>> ** frequently using Heising modulation
> That's only true in a few cases.  There was one design that followed
> that scheme but it didn't sell, and was abandoned for all the reasons
> any exciter driving an amp is not very good except maybe for brief
> "two way radio" applications.  Since we're not dispatching taxi cabs,
> it's of little interest.   The reasons were:  For broadcasting, poor
> reliability, heat, and inefficiency.   The overwhelming preference in
> broadcasting was high level plate modulated rigs.  Honestly Ron, for
> someone who says he has been in broadcasting 48 years, you seem to
> have a selective memory.   Let us take a look at one of these um, less
> than popular rigs, the Gates Vanguard 1, made and sold in the
> mid-1960s.  It ran a 100 w. s.s. exciter driving a 4cx3000 as a linear
> amplifier.   A hot and inefficient 1 KW rig (and if you ask me, one of
> the less attractive bc transmitters):
> http://www.w8bac.com/vanguard.html   I have never owned or operated
> one however, and the ham who owns this one may not have any issues
> with it, but I'd rather have an old Collins or RCA rig myself.
>
> 73
>
> Rob
> K5UJ
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