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 Post subject: WMBO Promotional Radio
PostPosted: Jun Sun 16, 2019 6:10 pm 
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Joined: May Thu 12, 2016 4:36 am
Posts: 68
Location: Niagara Falls, Canada
Picked up a promotional radio from WMBO Radio Station Auburn New York. It's a single am station radio 1340 mHz. radio is working however station is to far away to pick up signal clearly. Was wondering how hard it would be to change station from 1340 to 740 mHz.
See Pictures below

Thanks Sidevalvebob


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WMBO image 1.jpg
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WMBO image 2.jpg
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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Sun 16, 2019 6:33 pm 
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Posts: 33310
Location: SoCal, 91387
You might try adjusting one or both of the red cores; at least one would be the oscillator. You don't show a ferrite antenna, but assuming it has one, you can also try sliding the coil on it for best reception, once you have Zoomer radio dialed in.

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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Sun 16, 2019 10:54 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1863
Location: Near Portland, OR
Could you post the IC part numbers? (One starts with "CA", the other with "LM".) If you get the pin layout, you might be able to trace out which coil is the oscillator coil and which is the input frequency pre-selector. (The two white core coils are probably the IF adjusters.)


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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Mon 17, 2019 1:37 am 
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Joined: Dec Sat 21, 2013 5:15 am
Posts: 440
Location: Puyallup, WA 98371
I doubt that whoever made it only produced them to sell to stations on 1340, so it probably can be
easily moved to anything on the AM band.

Dale


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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Mon 17, 2019 2:47 am 
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Location: Ohio 45177
Wonder who made those? The construction does not say "cheap transistor radio" with good looking components and a tan fibreglass board instead of brown phenolic. I suppose it is possible that it is tunable to other frequencies but it might be limited range of adjustment I fear. I am just pondering that with a fixed value capacitor, I would be amazed if the RF coils have an adjustment range that covers the whole 540-1650 range. I have one of those little Bloomberg Radio promotional pocket sets. 1130 WBBR. It has a "fine tuning" control of very limited range.

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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Mon 17, 2019 4:08 am 
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Joined: May Thu 12, 2016 4:36 am
Posts: 68
Location: Niagara Falls, Canada
Thanks for the responses and questions.
- Fifties asked about antenna there is no Ferrite antenna just a clip on back to attached a antenna wire.
-Steve in Oregon asked about the IC Part numbers they are CA3088E and LM380N I have attached partial data sheets on both IC's below.
Still hoping I will be able to adjust the radio to 740 mHz but if the range is limited at least to a station in my area I can listen to.

Thanks
Sidevalvebob


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CA3088E image.jpg
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LM380N Image.jpg
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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Mon 17, 2019 5:37 am 
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Location: SoCal, 91387
If you Google CA3088E tunable circuit, images, you'll find a schematic for the chip and external components.

It doesn't look like there's an easy way to add tuning to it.

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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Mon 17, 2019 7:06 am 
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Location: Near Portland, OR
sidevalvebob wrote:
Still hoping I will be able to adjust the radio to 740 mHz but if the range is limited at least to a station in my area I can listen to.

Actually, retuning the oscillator and preselector coils might not work. You may need to increase the value of the fixed caps that have been installed in place of the tuning gang.

The CA3088 is a AM circuit used in stereo hi-fis, so it could tune at least 535-1605 kHz. The oscillator coil should be preset, usually to 1400 kHz, while the pre-selector was usually set to 1600 kHz.

The third page of the data sheet you attached shows that pin 2 is the RF input. It connects (in the schematic) through a .05 cap to the secondary of the pre-selector coil. The other end of that secondary connects to a tap of the oscillator coil primary. The converter output (pin 3) connects to the secondary of the oscillator coil. The other end of the secondary connects directly to the primary of the 1st IF coil. The secondary connects to pin 4. Pins 6, 7 & 8 connect to the second IF coil.

The tuning gang should connect across the primaries of both the oscillator coil and the pre-selector coil. But since this is a fixed-frequency receiver, there will be fixed caps across both primaries. Another fixed cap (probably a 600 kHz padder) is shown connecting one end of the oscillator coil and the tuning gang to ground.

Most post-war AM radios used 0-365 mmf tuning gangs. You might need to find one and do a little experimenting.


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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Tue 18, 2019 2:35 pm 
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Joined: May Thu 12, 2016 4:36 am
Posts: 68
Location: Niagara Falls, Canada
Update
Retuning the oscillator and preselector coils I'm able to tune in stations from around 950 am to 1450 am. I'm very suprised at the tuning range it maybe be a little bit broader but not receiving any strong signals at the ends of this range in my area. I'm using a very short external antenna wire. I think if I want to get 740 am I will need to change some of the fixed caps. Might just leave it on 1440 am alot of fifties music and sports and gives me a very clear strong signal and allows me to tune it back to 1340 am to keep it authentic.

Thanks everyone for all the responses.
Sidevalvebob


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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Thu 20, 2019 5:38 am 
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Joined: Jun Wed 14, 2006 11:49 pm
Posts: 7667
Location: Leo, IN or Zellwood, FL
sidevalvebob wrote:
Update
Retuning the oscillator and preselector coils I'm able to tune in stations from around 950 am to 1450 am. I'm very suprised at the tuning range it maybe be a little bit broader but not receiving any strong signals at the ends of this range in my area. I'm using a very short external antenna wire. I think if I want to get 740 am I will need to change some of the fixed caps. Might just leave it on 1440 am alot of fifties music and sports and gives me a very clear strong signal and allows me to tune it back to 1340 am to keep it authentic.

Thanks everyone for all the responses.
Sidevalvebob


I would bet that if you added an additional 100 pF mica cap in parallel with both the preselector and the oscillator coils that the set could then be peaked up on AM740.
John k9uwa

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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Fri 21, 2019 12:08 am 
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Joined: May Thu 12, 2016 4:36 am
Posts: 68
Location: Niagara Falls, Canada
Thanks John for your comment was wondering if I did add a mica cap where the best place to add it could I piggy back it off another cap that way I wouldn't have to alter the circuit board I included two pictures one of the front side of the circuit board with caps numbered and one of the underside. The values of the caps are as listed

1- .47 12v
2- .02 100v
3- .05 50v
4- .05 50v
5- .05 50v
6- .05 50v
7- .005 100v
8- .1 25v
9- .02 100v
10- .47 12v
11- .47 12v
12- 40 pf 100v
13- 22 pf ?v

Thanks
Sidevalvebob


Attachments:
WMBO image 2a.jpg
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Circuit Board Underside Image.jpg
Circuit Board Underside Image.jpg [ 246.56 KiB | Viewed 949 times ]
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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Fri 21, 2019 4:40 am 
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Location: Leo, IN or Zellwood, FL
sidevalvebob wrote:
Thanks John for your comment was wondering if I did add a mica cap where the best place to add it could I piggy back it off another cap that way I wouldn't have to alter the circuit board I included two pictures one of the front side of the circuit board with caps numbered and one of the underside. The values of the caps are as listed

1- .47 12v
2- .02 100v
3- .05 50v
4- .05 50v
5- .05 50v
6- .05 50v
7- .005 100v
8- .1 25v
9- .02 100v
10- .47 12v
11- .47 12v
12- 40 pf 100v
13- 22 pf ?v

Thanks
Sidevalvebob


all of the above capacitors are either bypass or coupling caps ... except #12 and #13 ... very small pF caps. Good guess says that the 40 pF is the Ant circuit and the 22 pF is the higher than Ant .. Oscillator circuit. And yes just carefully tac solder in parallel with these two. 100 pF might be too much? Look at it this way... one of those two red topped cans is the oscillator so that one will change the frequency of the receiver. The other one needs to peak up the signal at whatever frequency the oscillator is tuned to .. less of course the IF frequency. Put a 50 pF in parallel with each one of them... then fire up the radio and a signal generator ... tune about with the signal generator until you hear the signal in the radio .. then attempt to peak up the ANT section. Now walk the Oscillator and the signal generator down the band until you either get to the bottom where it won't go any lower ... or if you also get to a point where the ANT one won't peak up... By playing with a few small pF mica caps and a screwdriver and a signal generator very soon you will get the radio so that it does tune in 740 and the Ant circuit will peak up nicely at that same frequency.

Ignore the above 50 pF idea. Let the Frequency Calculator tell you what to add to those two caps

Take a look at this online frequency calculator. https://www.daycounter.com/Calculators/LC-Resonance-Calculator.phtml Wild Guess about your circuit ... the osc frequency is 450 khz ABOVE the incoming antenna radio frequency. Current Knowns are 22 pF and 40 pF ... and frequency that it will tune is from 950 to 1450 khz. 950 + 450 = 1450 and 1450 + 450 = 1900 khz. Midpoint where the stations you get can be peaked up... call it 1200 khz. and then the Osc would be 450 above 1200 = 1650. So into that calculator put in knowns of 1200 khz or actually 1.2 mhz and 40 pF and hit calculate .. whatever that number is in the other box is the inductance needed to peak up a signal at 1200 with a 40 pF cap. Let the calculator add the pF so remove the 40 pF ... change the frequency on the calculator to 0.8 mhz and hit calculate ... and the calculator now says you need a total of 90 pF. You have 40 pF so add 50 pF.

Next do the same thing with the oscillator. Clean off all the numbers. Put in 22 pF and 1.65 mhz and hit calculate .. it will calculate the L for inductance. We want to move the oscillator from 1.65 mhz to 450 less than that so put 1.2 mhz in the frequency box and hit calculate. Now it says that 22 pF cap needs to be 42 pF so add 20 pF to the 22 that is already in place... turn on the radio and see what you can tune and peak up now...

John k9uwa

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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Fri 21, 2019 7:42 pm 
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Joined: Feb Sun 02, 2014 9:13 pm
Posts: 2040
Location: Roanoke, VA
In the course of 50 years of working in radio and more than 30 years as a radio collector I have probably seen (in person or in photos) most of the microphone-shaped fixed-tuned novelty radios sold to radio stations for giveaways and branded with the station's call letters. I have seen that model before (a unique variant of models styled after the RCA 77-series microphones) but have never seen it identified with manufacturer or model number.

Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcityeng/index.html


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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Fri 21, 2019 11:25 pm 
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Joined: May Thu 12, 2016 4:36 am
Posts: 68
Location: Niagara Falls, Canada
-Thank You: John for sharing your knowledge I have learned so much since I've been on this site from people like yourself. I'm going out tomorrow to pick some caps up hopefully they have the ones I need. Will give it a try and post the results.

-In response to Dale's post there is no markings what so ever on the outside or the inside except for some numbers on the circuit board to indicate who or where this was manufactured. If I have the time I will trace the circuit board and make a wiring diagram.

Thanks
sidevalvebob


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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Sun 23, 2019 2:56 pm 
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Joined: May Thu 12, 2016 4:36 am
Posts: 68
Location: Niagara Falls, Canada
-Update
Following John's advice I piggybacked a 50pf and 20pf capacitor into the circuit, I can now receive 740 AM (Zoomer Radio) quite happy I think I will increase the length of the external antenna as well just to see if there is a little more increase in volume. at a later date I think I will replace the capacitors with something around 90pf and 42 pf just to clean things up where they are on the circuit board they are easy to remove and put new ones in.

Thanks everyone
sidevalvebob


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 Post subject: Re: WMBO Promotional Radio
PostPosted: Jun Sun 23, 2019 4:32 pm 
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Location: Leo, IN or Zellwood, FL
sidevalvebob wrote:
-Update
Following John's advice I piggybacked a 50pf and 20pf capacitor into the circuit, I can now receive 740 AM (Zoomer Radio) quite happy I think I will increase the length of the external antenna as well just to see if there is a little more increase in volume. at a later date I think I will replace the capacitors with something around 90pf and 42 pf just to clean things up where they are on the circuit board they are easy to remove and put new ones in.

Thanks everyone
sidevalvebob


Excellent Bob glad it works. My guess is when those radios were built that they had some table showing the proper pair of capacitors to install into those two slots based one frequency of the radio station who was purchasing them. Maybe 4 or 5 different pairs of capacitors plus the adjustment of the ferrite cores would handle all of the BC band.

Glad it worked out.
John k9uwa

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