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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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2nd Sep 2015, 10:13 am | #41 |
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Re: A frustrated Motorola
But do you agree that what we are looking at in the photos is not the same as the circuit diagram?
Mike |
2nd Sep 2015, 1:38 pm | #42 |
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Re: A frustrated Motorola
Yes, Mike. For a start the wiper (point 2) of the Volume Control, shouldn't be connected to the 'cold' side (point C) of the tone control. With the radio in front of me I could work out where the connections should go to agree with the circuit diagram, but basically the 'cold' side (point 3) of the V/C should go to AF Negative, and the wiper to R19/C22, whilst the wiper (point B) of the tone control should go to AF Negative. The usual way this is done is to link points B & 3 together, then take a wire from there to the AF Negative line on the PCB. A wire from point 2 should then go to R19 on the PCB.
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2nd Sep 2015, 6:35 pm | #43 |
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Re: A frustrated Motorola
This is all very helpful - I am actually quite sure now that someone has been in here before and botched the radio quite a bit because:
1. The soldering on the underside is particularly poor and unshiny on the output side. 2. Although you can't quite see it in the photos, someone has written something on the wall of the heat sink above the three output trannies TX6-8; something like "TX broken" |
2nd Sep 2015, 9:30 pm | #44 |
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Re: A frustrated Motorola
Just posting some more pics of the pot for further clarification ... hope this helps
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5th Sep 2015, 1:32 pm | #45 |
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Re: A frustrated Motorola
A frustrated Motorola no more ... as promised, I am happy to report a great success story.
Decided to replace TX6 (the "Corbyn") which I donated from my (non functioning) Motorola 112, which is virtually identical to this 114. And, hey presto, the 114 fired into glorious life! So i wanted to say: A BIG THANK YOU TO EVERYONE Just managing to fix this one has given me such confidence in this new hobby. Now to fix the 112! |
5th Sep 2015, 5:51 pm | #46 |
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Re: A frustrated Motorola
Congratulations on a success!
It's always satisfying to achieve something in a new 'hobby' - even if it's somewhat incidental to your main intentions. Be aware though - before long you'll get sucked into the historic radio-restoration-and-use game! [it's better than lying under a classic car in an inch of water in winter]. |
5th Sep 2015, 10:23 pm | #47 |
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Re: A frustrated Motorola
Having got the radio working I am trying to get a 3.5 Jack lead to play an iPhone through.
Here are two photos attached. The annotated one is a 114 I bought from eBay and a "pro" wired up. The 2nd photo is my attempt to copy this. But it doesn't work !!!! Any thoughts? |
6th Sep 2015, 1:08 am | #48 |
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Re: A frustrated Motorola
It certainly looks about right {assuming the red and white wires are the signals and the green wires are the returns, the combined signals go to the clockwise (live) tag and the returns to the anticlockwise (earthy) tag, which is right}; but is the junction of the two green wires touching against the middle (slider) tag of the potentiometer? If so, it will never work.
It probably would not be a bad idea to resolder those connections anyway, exposing as little bare wire as possible this time. While you have the leads disconnected, double-check the connections; which should be, white to the tip (left hand signal); red to the next contact along (right-hand signal); and both greens to the contact which would be joined to the body of a metal plug (common return). If it is mis-wired, again, it will never work.
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6th Sep 2015, 6:12 pm | #49 |
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Re: A frustrated Motorola
If I may point out a 'sticky' thread at the top of this section, in which I explain how I wire up various radios for 'aux-in' sockets.
https://www.vintage-radio.net/forum/...ad.php?t=87095 I usually, if not always, incorporate a 'radio-aux' switch, along with a 3.5mm stereo jack socket. There are two reasons I do this, one being that, AFAIK, 3.5mm switched jack sockets are unobtainable from any of the usual suppliers, the other being that the user can leave an I-pod or other device, plugged into the 'aux-in' socket, toggling between sources as desired. In recent times I've taken to using a 4-pole changeover switch, using two of the poles to ground the unwanted source. This prevents radio breakthrough. Last edited by Station X; 6th Sep 2015 at 9:31 pm. Reason: Link added. |
6th Sep 2015, 7:16 pm | #50 |
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Re: A frustrated Motorola
Re 3.5mm switched sockets. I don't know who the 'usual suppliers' are but the first 2 I looked at -- Maplin and Farnell -- both sell them. However, only as a chassis mounting part, I have never seen switched cable-mouting jack sockets in any size. If you need a cable one, I guess you could fit the chassis one in a suitable small container.
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6th Sep 2015, 9:05 pm | #51 |
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Re: A frustrated Motorola
Thanks All.
Livewire - do you have a picture of the switch and how it is mounted? I have studied the thread you mention for months, but I didn't find the pics were clear enough, even as someone familiar with the 114. Would you be able to annotate them at all? WOuld this have protected my phone jacks? thanks in advance |
6th Sep 2015, 9:37 pm | #52 | |
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Re: A frustrated Motorola
Quote:
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7th Sep 2015, 9:06 am | #53 |
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Re: A frustrated Motorola
I never have much luck attempting to annotate pictures, but will draw out a circuit diagram, and see if I can post that as soon as I can. In the meantime, to answer Newshound's question, the addition of a 'radio/aux' switch wouldn't have protected your phone jacks. The suggestion of including a blocking capacitor is a good one for preventing DC from getting where it shouldn't. Including series resistors of between, say 1 and 10k per channel is a must when connecting a stereo source such as an Ipod to a mono radio.
Basically, what I do is remove the original connection from the detector circuit of the radio from the top of the volume control pot., and connect the lead from the jack socket to the v/c via the switch, so that, when listening to an external source it isn't necessary to try and find a 'quiet' spot on the MW band, if such a thing even exists any more! |
7th Sep 2015, 12:16 pm | #54 |
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Re: A frustrated Motorola
You can annotate by opening the picture in Paint, then just draw lines in a contrasting colour and add text as required.
Can't demo- using a tablet which is useless for drawing stuff.
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7th Sep 2015, 12:29 pm | #55 | |
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Re: A frustrated Motorola
Quote:
Add a capacitor as well? What exactly does a "blocking capacitor" mean? eg. presumably not an electrolytic but a small ceramic? If so, what rating should it have? TIA |
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7th Sep 2015, 2:47 pm | #56 |
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Re: A frustrated Motorola
You don't need resistors in the earth returns.
Just connect a 1 kΩ resistor in series with each of the white and red wires; join the other ends of the two resistors and take this point to one lead of a 470 nF capacitor (this value won't be electrolytic, so it will be fine either way around); and the other capacitor lead to the volume control clockwise terminal. That setup ought to protect the phone against most eventualities: the resistors prevent too much current being drawn from the outputs if they are trying to assume different voltages, and the capacitor blocks any DC that may be presenton either side from upsetting anything on the other side. Note, be sure not to let the resistors and capacitor short-circuit gainst anything else! You may want to mount them on a small piece of Veroboard, and connect this to the volume control with a short length of shielded cable.
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7th Sep 2015, 3:03 pm | #57 |
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Re: A frustrated Motorola
Brilliant, thanks Julie.
Out of interest: why do I need a resistor for the white and red - they are twisted and soldered together anyway, so why not just put one (or one that is 200k) between the twisted-together wires and the tag? Also, for future reference, how do you calculate the capactior as 470 nF? Always good to know the theory! Thanks again |
7th Sep 2015, 3:57 pm | #58 |
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Re: A frustrated Motorola
I may have posted the drawing I did in the wrong thread.
1k or 2.2k the value is not too important. I left the value of the capacitor out of the drawing to see what others said but i would agree 0.47uF or 470nF should do fine. Mike |
7th Sep 2015, 4:33 pm | #59 |
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Re: A frustrated Motorola
Each signal needs to go via the same value resistance to the common junction point. If the resistors are different, one channel will make more contribution than the other to the combined signal.
The fact of the red and white being twisted together in the first place is what broke your phone ..... With effectively 2 kΩ between the red and white wires, you cannot get excessive current flow if one channel is driven low while the other is being driven high. 470 nF is an educated guess; and in any case, the value is not massively critical. If it is too small, you will lose low frequencies.
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7th Sep 2015, 10:31 pm | #60 |
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Re: A frustrated Motorola
Is it ok to leave the two green return wires twisted together ?
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