[AMRadio] Broadcast Processors

Tue Jun 14 13:30:07 EDT 2011

curious about what killed the 4-1000s, did they have propper airflow and 
normal plate current?  AB2 can develope 3800 w of audio at 6kv  that should 
be a good match for 5 kw out.
did you ever ask Eimac about this?
From: "Dennis Gilliam" <dennisgilliam at gmail.com>
To: "Discussion of AM Radio in the Amateur Service" 
<amradio at mailman.qth.net>
Sent: Tuesday, June 14, 2011 1:04 PM
Subject: Re: [AMRadio] Broadcast Processors

>A short story about an AM transmitter:
>
> Years ago I was CE for KZZP-AM in Mesa, AZ.  The station had a Bauer 5kW,
> and management wanted it to be 'louder'.
>
> Replacing the old, single-band limiter, I installed a CRL set of three 
> units
> (AGC, EQ, and limiter), the usual setup.
>
> Wow, what a difference that made!  It still didn't please the program
> director, so I got Ron Jones (the owner of Circuit Research Labs) to come
> out and take a look.  He said 'This transmitter has the worst bottom end
> tilt I've ever seen'.
>
> He went back and cooked up an experimental box we installed the next week,
> and boy, did it sound really good & loud.  Lots of mod plate glow, BTW.  A
> week later, the 4-000 modulators were flat.  I didn't think that was too
> bad, as they had been in service for some time.
>
> I put in a new set, things were good again.  Boy, those Eimacs were really
> working for a living, I thought.
>
> Two weeks later, they looked like old coffee pots, brown from ion burns 
> and
> totally without emission--again.  I mentioned this to the PD, and that 
> this
> will cost some $.  He said, 'Don't worry about it, we are going to make a
> bundle!'
>
> New tubes were ordered up, and in went my last spares.  The same drill 
> went
> down, those tubes died in two weeks.  More tubes installed.  More great
> glow....
>
> Then the office manager asked me about the invoices she was getting from
> Richardson Electronics for all those 4-1000's.  I told her the story.  She
> went to the boss, and that started a loud argument between her and the PD
> about the $$ out vs. the $$ in.
>
> The big boss found for her, and the 'magic box' from CRL was retired and 
> mod
> tubes went back to lasting about a year or so.
>
> The lesson of TANSTAAFL applied to transmitters.
>
> 73DG
>
> On Tue, Jun 14, 2011 at 7:45 AM, Jim Tonne <Tonne at comcast.net> wrote:
>
>>
>> Regarding commercial broadcast processors for ham use.
>>
>> > The transmitter "Frequency response must be less than
>> > 3dB down at 0.15Hz, and less than 0.1dB down at 9.5 kHz."
>>
>> That figure of 0.15 Hz may sound odd and arbitrary but is
>> based on a direct-coupled modulator (i.e., flat down to DC)
>> with a one-second time-constant on an input blocking
>> capacitor and resistor.
>>
>> That figure of 0.15 Hz is sometimes specified in the contract
>> between the manufacturer and the purchaser.
>>
>> Another way the low end is sometimes specified is that if
>> the transmitter is modulated with a 50 Hz square wave that
>> the tilt on the resultant modulation is to be less than 2%.
>>
>> Why this "nonsense" you may ask.   It is because the
>> commercial broadcast processors  generally deliver an
>> output waveform that is somewhat clipped, although it
>> may be clipped only on transients.   For them to control
>> the modulation requires that the following audlio stages
>> (the modulator) have such a flat response.
>>
>> Another area that is of concern in the transmitters is the
>> insistence by the purchaser that the response be flat on
>> the high end and yet have no overshoot on a 2 kHz
>> squarewave.   Can't do that and when the manufacturer
>> sits down with the purchaser and explains the math,
>> the purchaser comes away enlightened and happy.
>>
>> - Jim Tonne   used to design BIG PWM rigs at CEC
>>
>>
>>
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