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 Post subject: Re: Frequency response of 30's radio
PostPosted: Sep Tue 20, 2011 4:38 pm 
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radioterry wrote:
Alan Douglas wrote:
Attachment:
Philco_95_response.jpg
From RADIO, March 1930.


Alan:

Thanks.

You not only answered the OP, but you now have me wanting to pull my Philco 95 out of the to do later when I can group and move it up to the to do next group. I didn't realize that it had the potential to be such a nice performing radio!

BR,

Terry


You should take that curve with a serious grain of salt. Nobody was actually doing acoustical measurements back then (except maybe Bell Labs) so those curves are theoretical at best. More likely just marketing material.

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 Post subject: Re: Frequency response of 30's radio
PostPosted: Sep Tue 20, 2011 4:54 pm 
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That was electrical response, not acoustical.


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 Post subject: Re: Frequency response of 30's radio
PostPosted: Sep Tue 20, 2011 5:22 pm 
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Alan Douglas wrote:
That was electrical response, not acoustical.


Alan, I've heard comments that A. Kent got upset when his engineers attempted to improve
the high-end fidelity of his receivers, preferring a more mellow sounding receiver with the
highs severly rolled off.
Any truth to that, or is it urban legend?

Pete

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 Post subject: Re: Frequency response of 30's radio
PostPosted: Sep Tue 20, 2011 5:30 pm 
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Peter Bertini wrote:
Alan Douglas wrote:
That was electrical response, not acoustical.


Alan, I've heard comments that A. Kent got upset when his engineers attempted to improve
the high-end fidelity of his receivers, preferring a more mellow sounding receiver with the
highs severly rolled off.
Any truth to that, or is it urban legend?

Pete


I don't have the definitive answer, but I know a lot of people who service Atwater Kent 55's and 60's -- seems one of the first things they do is remove the "quality condenser" in the audio output to improve the highs. Personally I have a 60 with it still installed; prefering to keep the radio sounding as originally intended.

I think the attitude of many back in the day was to reduce the highs, most likely to reduce objectionable distortion and noise in the process. Mellow gave the impression of better performance.

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 Post subject: Re: Frequency response of 30's radio
PostPosted: Sep Tue 20, 2011 5:36 pm 
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Alan Douglas wrote:
That was electrical response, not acoustical.


That is what I took it as...


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 Post subject: Re: Frequency response of 30's radio
PostPosted: Sep Tue 20, 2011 5:39 pm 
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Alan Douglas wrote:
That was electrical response, not acoustical.


Yes, that's what I figured. But no mention of where in the circuit the measurement is being taken. My point is that you have to listen through the speaker, so it isn't very meaningful on a practical level.

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 Post subject: Re: Frequency response of 30's radio
PostPosted: Sep Tue 20, 2011 6:39 pm 
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radioterry wrote:

Alan:

Thanks.

You not only answered the OP, but you now have me wanting to pull my Philco 95 out of the to do later when I can group and move it up to the to do next group. I didn't realize that it had the potential to be such a nice performing radio!

BR,

Terry


Terry, I think you wikll be pleasantly surprised at the performance of the 95. If your speaker is original and in good shape, it will be a nice radio to listen to!

-Steve

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 Post subject: Re: Frequency response of 30's radio
PostPosted: Sep Tue 20, 2011 11:09 pm 
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Quote:
Alan, I've heard comments that A. Kent got upset when his engineers attempted to improve
the high-end fidelity of his receivers, preferring a more mellow sounding receiver with the
highs severely rolled off.
Any truth to that, or is it urban legend?

It's true. John Dreyer, one of AK's engineers, told me the story. Seems that John M. Miller (of "Miller effect" fame) who was AK's chief engineer wanted to make a high-fidelity set and presented a prototype to Kent. Kent had a listen and immediately told Miller "I'll have to take a baseball bat to you" and then gave the set to Dreyer with the instructions "You know what I want." Dreyer put a large capacitor across the output plate to kill the treble and Kent was happy.

That was what most buyers wanted at the time, and broadcast transmitters had pretty ugly distortion up there.

Grebe was the other proponent of good treble response.


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 Post subject: Re: Frequency response of 30's radio
PostPosted: Sep Wed 21, 2011 12:41 am 
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Alan, could that radio have been what became the 711?

it was a pretty high end radio with 2A3s.

-Steve

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 Post subject: Re: Frequency response of 30's radio
PostPosted: Sep Wed 21, 2011 3:31 am 
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Gary Tayman wrote:
SO -- since radio receivers, in the interest of selectivity, and in the interest of keeping that 10kHz whistle to a minimum, limit their response to around 5,000 Hz (or less) anyway

Actually, high fidelity AM tuners have a 10KHZ notch filter in the audio to remove the whistle. The notch filter creates a very deep but very narrow notch in the frequency response. There is no need to limit the bandwidth to below 5 KHZ to eliminate the whistle.

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 Post subject: Re: Frequency response of 30's radio
PostPosted: Sep Wed 21, 2011 1:12 pm 
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Magnavox and other makers of wide-band sets often included a 10 kc trap in one of the audio stages to eliminate the adjacent channel carrier heterodyne. Listening to a station whose transmitted response extends to at least 10 kc (Canada's AM 740, for example) demonstrates how really good AM can sound on one of these radios.

Moving ahead to more modern times, there was a resurgence in improving AM by adding stereo. During what I call the "experimental AM stereo period" in the late '70's, Sony introduced several models capable of wide-band reception. Listening to a stereo AM station using the Kahn independent sideband system with 10 kHz response on this model SRF-A100 was a real eye and ear opening experience.


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