Antique Radio Forums
https://www.antiqueradios.com/forums/

Dial scale on radios of the 1920's
https://www.antiqueradios.com/forums/viewtopic.php?f=1&t=384675
Page 1 of 1

Author:  IGot2P [ Sep Fri 25, 2020 3:43 am ]
Post subject:  Dial scale on radios of the 1920's

I realize that the 0 to 100 scale on the radios in the 1920's is simply a reference scale for logging but is there any relation between that old scale and the actual KHz broadcast signal? I have several radios of that era where I can move the dial pointers to wherever I want but I would like to have them in some type of relation to the actual broadcast signal. For example, I currently am getting the following:

19 = 1120 KHz - St. Louis, MO
32 = 930 KHz - Quincy, IL
45 = 820 KHz - Ft.Worth, TX
62 = 720 KHz - Chicago, IL
73 = 650 Khz - Nashville, TN

I suspect that this question has been beat to death over the years but Googling was not coming up with a definitive answer for me.

Don

Author:  egg [ Sep Fri 25, 2020 3:49 am ]
Post subject:  Re: Dial scale on radios of the 1920's

Your "62" is incorrect... :shock:
viewtopic.php?p=2092864#p2092864

:) Greg.

Author:  JnTX [ Sep Fri 25, 2020 4:13 am ]
Post subject:  Re: Dial scale on radios of the 1920's

egg wrote:
Your "62" is incorrect... :shock:

Maybe he has a notch in the capacitor plates.

If the capacitor has no stops so it will turn 360 degrees, you can move the dial around 180 degrees and the dial numbers will increase with frequency.

Jay

Author:  IGot2P [ Sep Fri 25, 2020 5:11 am ]
Post subject:  Re: Dial scale on radios of the 1920's

JnTX wrote:
egg wrote:
Your "62" is incorrect... :shock:

Maybe he has a notch in the capacitor plates.

If the capacitor has no stops so it will turn 360 degrees, you can move the dial around 180 degrees and the dial numbers will increase with frequency.

Jay


No capacitor plates on a Magnavox Type T.R.F 5 Model 5 which I was using.

Don

Author:  Indiana Radios [ Sep Fri 25, 2020 5:35 am ]
Post subject:  Re: Dial scale on radios of the 1920's

IGot2P wrote:
45 = 820 KHz - Ft.Worth, TX


Different radios track differently. One make and model of radio could tune in 820 KHz at the 45 mark on it's dial while a different make and model of radio might tune in 880 KHz at the 45 mark on it's dial. One radio might tune in 1400 KHz at the 100 mark on it's dial while another radio might tune in 1500 KHz at the 0 mark of it's dial. The plates on various brand name tuning capacitors are not all of the same shape so tracking varies from one brand of tuning cap to another. Some tuning capacitors are linear in tuning (stations are evenly spaced apart) while other tuning capacitors are non linear in tuning (stations vary in distance from each other).

Author:  homebrew [ Sep Fri 25, 2020 8:22 am ]
Post subject:  Re: Dial scale on radios of the 1920's

Dial logs came with the radios.
A few had paper inserts to put behind or under the dial hands to mark stations.
Dials with frequency marked on them were available for most of the popular single dial sets from a couple parts companies. The Atwater Kent frequency dial I have is right on. I have a black one designed for a unknown set that was close on a AK set on the low frequencies and way off at the top of the band.

Author:  Alan Voorhees [ Sep Fri 25, 2020 9:40 am ]
Post subject:  Re: Dial scale on radios of the 1920's

1-100 is a big improvement over setting three dials.

Author:  jrehkopf [ Sep Sun 27, 2020 6:24 pm ]
Post subject:  Re: Dial scale on radios of the 1920's

I have quite a number of three-dialers and some one dials of this era, and they all are a bit different, sort of like cats. Most of them have low frequency stations at the 80-100 end of the dial; I have a couple that are exactly backwards of that.

Pretty consistent that 550 khz will be between 90 and 80 on the dial. This is starting with the dials at 100 and the tuning elements completely meshed. Then, as I go up in frequency there is a difference in frequency/dial numbers that depends on the total tuning range of that particular radio/antenna combination.

If the range tops out at about 1250 khz then 800 khz is about 40-45 on the dial. If the range tops out at 1500 then 800 khz is around 55-65 on the dial.

Seems like when the broadcast band became more standardized in range, single dial tuning got figured out, then frequency markings begin to appear on dials (1926-1927??).

Here is a chart of Don's frequencies, and a photo of a Sparton 6-15 tuning dial, 1927, marked in meters and frequency.
Attachment:
File comment: Wurlitzer tuning chart.
Picture1.jpg
Picture1.jpg [ 18.75 KiB | Viewed 977 times ]

Attachment:
File comment: Sparton 6-15 tuning dial
DSC02109.JPG
DSC02109.JPG [ 619.66 KiB | Viewed 977 times ]

Author:  homebrew [ Sep Mon 28, 2020 4:25 am ]
Post subject:  Re: Dial scale on radios of the 1920's

The bands were standardized by the govt in late 23.
The early radios covered the bands just below the current broadcast band that had government weather, farm reports, and time.

Author:  SmoothOscillator [ Sep Mon 28, 2020 1:46 pm ]
Post subject:  Re: Dial scale on radios of the 1920's

Quote:
tuning capacitors are non linear in tuning


I believe my Radiola 60 is like that; at one end of the dial stations are relatively crammed together with respect to the other end.

Author:  khutch [ Sep Mon 28, 2020 3:40 pm ]
Post subject:  Re: Dial scale on radios of the 1920's

IGot2P wrote:
I realize that the 0 to 100 scale on the radios in the 1920's is simply a reference scale for logging but is there any relation between that old scale and the actual KHz broadcast signal? I have several radios of that era where I can move the dial pointers to wherever I want but I would like to have them in some type of relation to the actual broadcast signal. For example, I currently am getting the following:

19 = 1120 KHz - St. Louis, MO
32 = 930 KHz - Quincy, IL
45 = 820 KHz - Ft.Worth, TX
62 = 720 KHz - Chicago, IL
73 = 650 Khz - Nashville, TN

I suspect that this question has been beat to death over the years but Googling was not coming up with a definitive answer for me.

Don


In the early days it was much more common to talk about wavelength than it was to talk about frequency. Therefore on many early radios with logging scales instead of "calibrated" scales the higher numbers represent higher wavelengths which of course are lower frequencies. This is quite backwards to modern thinking which has long since shifted to frequency. And there are some old radios with logging scales where the higher numbers represent higher frequencies.

In terms of wavelength your list becomes:

19 = 268 meters - St. Louis, MO
32 = 322 meters - Quincy, IL
45 = 366 meters - Ft.Worth, TX
62 = 416 meters - Chicago, IL
73 = 461 meters - Nashville, TN

Also, in the early days variable capacitors tended to be made to be roughly linear in capacitance change as the shaft was rotated in even increments of degrees. This produces the crowding you will see on one end of the dial because the resonant frequency varies as the square root of the capacitance. If you look at old magazines you will see ads for radios that use "straight line" capacitors as well as for the capacitors themselves for DIY use. These capacitors had very exotically shaped moving plates that would give you a very straight line curve of rotation versus frequency. Modern variable capacitors have for the most part returned to semicircular plates but with the the tuning shaft offset which gives you an approximately straight line tuning curve that is close enough for most applications.

Author:  engineer [ Sep Mon 28, 2020 11:33 pm ]
Post subject:  Re: Dial scale on radios of the 1920's

My refurbished 1927 Kolster 6L
Canadian AM stations near Toronto:
Frequency (KHz)... Dial (+/-)
1050... 2.2
1010... 2.5
CBC (french)... 3.75
740... 5.2
680... 6.3
640... 7.1
590... 8.25

Cheers,
Roger

Page 1 of 1 All times are UTC [ DST ]