[AMRadio] Broadcast Processors

Tue Jun 14 17:08:32 EDT 2011

Those transmitters did not go near DC. The low end response would be 
limited before it got near the high powered stuff.

On 6/14/11 4:59 PM, Bernie Doran wrote:
> interesting!  Just does not seem logical. The mod transformer would probably
> go down to 30 cy or less and probably the audio low cut off was not much
> below that.   my Gates COG also has cathode follower drivers, a great way to
> drive class BE.   Wonder if there was some component( with all that
> processing)  that was near DC and ended up as dissipation. That should have
> been obvious from color
> ----- Original Message -----
> 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 1:47 PM
> Subject: Re: [AMRadio] Broadcast Processors
>
>
>> Ron and I looked this over carefully.  No airflow problems, and the mod
>> trans was OK, a oil-filled Electro job.  The duty cycle was tough, with
>> the
>> mod current meters just never moving off max except total silence.
>> Positive
>> peaks were around 120%.  The compression ratio was really high, and the
>> program density and bottom end correction was right on the edge of
>> negative
>> overmod.  This TX even used the iron-free 'transparent' cathode-follower
>> mod
>> driver setup.
>>
>> Some combinations of parts called transmitters are not meant to
>> have asymmetrical positive peak ability.
>>
>> Years later I saw the same characteristics on a CCA 5kW.  It had the same
>> tube compliment, 2X4-1000 modding a single 4CX5,000.  It couldn't handle
>> +peaks without tripping the OL relays.  They tried previouly, and had to
>> buy
>> all new mod iron.
>>
>> 73DG
>>
>> On Tue, Jun 14, 2011 at 10:30 AM, Bernie Doran<
>> qedconsultants at embarqmail.com>  wrote:
>>
>>> 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
>>>>>
>>>>>
>>>>>
>>>>> ______________________________________________________________
>>>>> Our Main Website: http://www.amfone.net
>>>>> AMRadio mailing list
>>>>> Searchable Archives:
>>> http://www.mail-archive.com/[email protected]/
>>>>> List Rules (must read!): http://w5ami.net/amradiofaq.html
>>>>> List Home: http://mailman.qth.net/mailman/listinfo/amradio
>>>>> Post: AMRadio at mailman.qth.net
>>>>> To unsubscribe, send an email to amradio-request at mailman.qth.net with
>>>>> the word unsubscribe in the message body.
>>>>>
>>>>> This list hosted by: http://www.qsl.net
>>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>>>
>>>> ______________________________________________________________
>>>> Our Main Website: http://www.amfone.net
>>>> AMRadio mailing list
>>>> Searchable Archives:
>>> http://www.mail-archive.com/[email protected]/
>>>> List Rules (must read!): http://w5ami.net/amradiofaq.html
>>>> List Home: http://mailman.qth.net/mailman/listinfo/amradio
>>>> Post: AMRadio at mailman.qth.net
>>>> To unsubscribe, send an email to amradio-request at mailman.qth.net with
>>>> the word unsubscribe in the message body.
>>>>
>>>> This list hosted by: http://www.qsl.net
>>>> Please help support this email list: http://www.qsl.net/donate.html
>>> ______________________________________________________________
>>> Our Main Website: http://www.amfone.net
>>> AMRadio mailing list
>>> Searchable Archives: http://www.mail-archive.com/[email protected]/
>>> List Rules (must read!): http://w5ami.net/amradiofaq.html
>>> List Home: http://mailman.qth.net/mailman/listinfo/amradio
>>> Post: AMRadio at mailman.qth.net
>>> To unsubscribe, send an email to amradio-request at mailman.qth.net with
>>> the word unsubscribe in the message body.
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>>
>> ______________________________________________________________
>> Our Main Website: http://www.amfone.net
>> AMRadio mailing list
>> Searchable Archives: http://www.mail-archive.com/[email protected]/
>> List Rules (must read!): http://w5ami.net/amradiofaq.html
>> List Home: http://mailman.qth.net/mailman/listinfo/amradio
>> Post: AMRadio at mailman.qth.net
>> To unsubscribe, send an email to amradio-request at mailman.qth.net with
>> the word unsubscribe in the message body.
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
> ______________________________________________________________
> Our Main Website: http://www.amfone.net
> AMRadio mailing list
> Searchable Archives: http://www.mail-archive.com/[email protected]/
> List Rules (must read!): http://w5ami.net/amradiofaq.html
> List Home: http://mailman.qth.net/mailman/listinfo/amradio
> Post: AMRadio at mailman.qth.net
> To unsubscribe, send an email to amradio-request at mailman.qth.net with
> the word unsubscribe in the message body.
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>