[poulsbobill]

I  have a 37-116.  The magnetic tuning works but i have a "understanding" question.
I have read some theory etc on line but...

The alignment instructions say that when you turn off  the magnetic tuning there should be no
change in tone response.  Im having a hard time understanding this.  If the purpose of the magnetic tuner is to get to and keep the exact center of the broadcast, then when it is turned off  would not treble decrease?  -- because you are now not perfectly centered?  ( ie back to manually tuning) 

SO, If i am not likely perfectly centered  (manually) and especially if i have the treble/selectivity  knob to the widest band,  then i would be outside of the 10khz broadcast  range on one side. If  I turn off the magnetic tuner,  i  am now off-centered and dont get both sides of the  end of band (treble).  Thus tone would change.

The opposite when i turn it on?  I should hear a more tone (treble)  change because i now am getting the whole band because i am centered. 

Sorry newbie question, i am obviously missing something.

Bill

[vinzer]

Tune in a station with it off then turn it on should be no change in sound if there is it is not working right.

[morzh]

Yes, I suspect Vinzer is right.
Ideal manual tuning with MT off should then sound the same as when you turn MT ON.
Opposite cannot be true.
When you tuned using magnetic tuning and the Robo-dial, then when you turn MT off, and there is an error in tuning your sound will change to the worse.

[rfeenstra]

When you tune the radio in to a particular station, you will align to maximum signal. Then when you align the MT you will align the MT system to maximum signal. Since this is done well after the radio has had a chance to warm up, and not enough time for the oscillator to drift, the 2 signals should be exactly the same with no tonal difference. Once the MT is set, you will be able to turn the radio on when cold and the MT will bring the oscillator to the correct frequency for maximum signal given your dial setting for the station. then, as the radio warms up and the oscillator tends to drift, the MT will adjust the oscillator to maintain the maximum signal. It works well. I have 2 37-116's and a 38-116 and when properly adjusted, the MT keeps the signal strong and clear.

As morzh said, if you tune in a station with the MT on, It may lock in with the dial slightly off the correct frequency. Always tune with the MT off. the MT will then hold the frequency even if the local oscillator drifts, which it does do as the radio warms up.

[poulsbobill]

Yes it is a wonderful system.  i use it.
My misunderstanding is with the alignment instructions.  

 The alignment instructions say that when you turn off  the magnetic tuning there should be no
change in tone response.  Im having a hard time understanding this.  


If the purpose of the magnetic tuner is to get to and keep the exact center of the broadcast, then when it is turned off  would not treble decrease?  -- because you are now not perfectly centered?  ( ie back to manual  tuning and i am assuming i cant get it perfectly centered.)  So then i am not receiving the entire band evenly manually thus less treble.

And in reverse when you turn MT on should not treble go up as the radio is now centered on the band? (assuming you were not perfect in your manual tuning).

It may just be semantics here or a misplaced word in the alignment instructions but  do you see what i am saying here?

Thanks

Bill

[morzh]

Bill

Perhaps they meant it during the MT alignment.
I did that 4 years ago the last time and so I do not remember the details.
But if you follow procedure, as I remember, it worked exactly as described.

[Ron Ramirez]

MT = Magnetic Tuning

And Mike is correct, of course. The Philco alignment instructions are referring to the "change in tone" during alignment of Magnetic Tuning.

Perhaps the Philco people who wrote that up could have worded it better, such as "no change in tuning of the test signal". It really has nothing to do with treble (or bass), but the accuracy of the tuned-in signal.

[poulsbobill]

So it seems i am getting tone vs broadcast mixed up here. In fact they do say tone. ( and of course that would be very narrow).
I would think on turning the MT on, treble response would go up
then on a broadcast as the tuner would be centered on the broadcast and thus both ends of the band will be received. I think i read the 37-116 has a 9+khz breadth in wide mode.

Thanks

Bill

[rfeenstra]

Remember, no broadcast stations have a frequency response greater than 5 khz today. The only way to enjoy the 9+khz bandwidth is to broadcast your own signal. I do that and the sound is remarkable for a 1938 radio.

It is possible to manually tune to the exact frequency of the broadcast station. Then, when the MT is engaged, it should not change the local oscillator frequency and there will be no change in how the signal sounds. However, if the MT is not aligned properly, turning on the MT will actually pull the oscillator off from the proper frequency resulting in a slightly detuned station and the sound will be affected, same as it is if you manually detune the station with the MT off. It is possible to use this fact to align the MT, adjusting the MT transformer for no tonal change when switching the MT on and off. In general though, better to use a signal generator and a meter to monitor output.

[BrendaAnnD]

This is not true. There are still a number of AM broadcast stations that are pushing out 10KHz audio (full 20 KHz bandwidth.) You can tell which ones they are if you use an SDR

[rfeenstra]

Brenda, I was not aware of that! I'm gonna google that to se if any are in my area. Thanks for the info.

[rfeenstra]

Brenda, I've been trying to understand this. It appears we are entering the world of Hybrid Digital AM radio, Software Defined Radio, etc. Can our old radios with a standard detector take advantage of any of this? Or are we still limited to the 10khz spacing (5khz audio) with our old, analogue sets? Can a standard AM radio take advantage of the expanded bandwidth of digital AM? I need education!! Point me to some relative info. Everything I've read points to an analogue signal of 5khz. Thanks!

(perhaps this should go in a separate thread)

[BrendaAnnD]

rfeenstra,

The shortest answer is yes and no.

1) The stations that are still doing wideband AM are generally the larger stations, though this is by no means a given. A standard envelope detector can take full advantage of these stations, but for most radios, the audio bandwidth is limited by the bandpass of the IF chain, usually about 4 KHz or so, since most radios were made to be able to separate stations, and not worry about hi-fi audio.

That being said, there were a number of high-end 1930's sets that had variable bandwidth that, when set to wide band/hi-fi would do a fine job and sound nearly as good as FM on a local signal. There are still a few radios out there that will take advantage of broadband AM, such as some of the CCranes and the Superadio III.

2) Our old radios are completely useless and will not see any advantage to I-BLOCK (IBOC/HD.) The stations using I-BLOCK all have a very narrow AM bandwidth, because the sidebands are used for the digital signal. In fact, a decent hi-fi AM radio will actually see a degradation of what AM audio they do have, since the wider IF bandwidth passes the digital signal, which comes out as a sort of a hiss that vaguely reminds one of the noise an old dial-up modem used to make. Oh, and 5KHz audio on I-BLOCK stations is a pipe dream, it's closer to 3.5.

[rfeenstra]

I have many variable bandwidth radios in my collection including Philco's, EH Scott's , and McMurdo Silvers that could take advantage of any wideband stations that might broadcast wider than the normal 10khz. where can one find info on what stations these are? Every thing seems to be spaced at 10khz increments for analogue AM. I can't seem to find them by searching the internet. They don't seem to give out that info.

for me , this is interesting stuff! I hope others get something out of it as well.

[morzh]

Rob


Our local 1160AM WOBM sounds just great. I am not sure what band is there though.