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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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28th Mar 2017, 7:03 pm | #21 |
Dekatron
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Re: Bush TR82 radio - why is power supply reversed?
Have I missed something or are you running this on a five volt power supply? Mick.
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28th Mar 2017, 7:04 pm | #22 |
Rest in Peace
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Re: Bush TR82 radio - why is power supply reversed?
A point regarding Earth Polarity. Many Car radios made in the mid to late 60s used PNP Transistors, so the Negative side was the supply rail as has been mentioned, but these radios were also Dual Polarity, so could be set for either Positive or Negative Earth. Service sheets usually gave the readings as being Negative w.r.t. the Positive line.
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28th Mar 2017, 7:42 pm | #23 |
Heptode
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Re: Bush TR82 radio - why is power supply reversed?
The emitter of any circuit always goes to the polarity of the emitter for the transistor to function, a P emitter goes to the plus rail, an N emitter goes to the minus rail. Radios like this should remain original without additions or modifications, just my opinions on this. If the detector diode is faulty a temporary bridge with an OA90 diode or similar germanium diode will show if this is where a fault is. It tends to be cheap radios that use two legs of a transistor junction as a diode that suffer this failure more.
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28th Mar 2017, 8:22 pm | #24 |
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Re: Bush TR82 radio - why is power supply reversed?
Yes, Mick - for convenience in testing as I do not have a 9V battery to hand. Of course all the voltage readings are 5/9s lower than quoted but nevertheless I am getting a very acceptable volume output.
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28th Mar 2017, 9:33 pm | #25 |
Dekatron
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Re: Bush TR82 radio - why is power supply reversed?
Stick two 5V PSUs in series with a silicon diode?
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28th Mar 2017, 9:48 pm | #26 | |
Heptode
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Re: Bush TR82 radio - why is power supply reversed?
Quote:
A lot of ladies do seem to have done a lot of this type of assembly work - photos of the Philco 444 ['Peoples Set'] assembly line in Greenford don't feature any men at all. Maybe the ladies were more patient and attuned to these repetitive tasks? Certainly, in most instances, they made a pretty neat and tidy job of things.
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Red to red, black to black. Throw the switch and stand well back! |
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29th Mar 2017, 6:54 am | #27 |
Rest in Peace
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Re: Bush TR82 radio - why is power supply reversed?
I would get a 9 volt supply before going too far and before you start replacing components.
I have had about 4 of these sets pass through my hands and none have needed any capacitor changes, so far, but the red and black capacitors can be iffy after all this time. So use a decent 9 volt supply to give them a chance of reforming. Any wax or paper capacitors will probably be OK as well, the low voltage in these transistor sets does not result in a lot of leakage. I like to insert an amp meter in the 9 volt supply, it will give you a good indication of the health of the circuit and components as you turn the radio on. (as well as later checking voltages on the various points around the transistors). You can sometimes pickup decent lab type variable low voltage supplies (0 to 30 volts) for not a lot. By the way it is important to not damage the black point on the transistors as they are light sensitive inside and can generate noise if light leaks in. Nice radios to work on, and also fairly decent sound as well. Mike |
29th Mar 2017, 10:32 am | #28 | |
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Re: Bush TR82 radio - why is power supply reversed?
Quote:
Lawrence. |
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29th Mar 2017, 1:09 pm | #29 | |
Heptode
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Re: Bush TR82 radio - why is power supply reversed?
Quote:
On the subject of those Ge diodes [AKA detectors] ... I have also had need to replace one or more of the FM discriminators in Bush VTR 103's ....... Finally, in every instance - I've had to replace the tuning cap suspension. This can actually be done without removing or de-soldering the component itself - careful severing of the old fibre grommets [with a craft knife or razor blade] and replacing with an appropriately sized neoprene grommet one at a time is my preferred MO. This measure will prevent the tuning scale needle and dial knob ultimately scratching and removing the scale legend etc. etc.
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29th Mar 2017, 6:08 pm | #30 | |
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Re: Bush TR82 radio - why is power supply reversed?
Quote:
Apart from reducing the max volume by using 5V instead of 9V is there any other disadvantage to changing its original supply like this? |
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29th Mar 2017, 6:19 pm | #31 |
Heptode
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Re: Bush TR82 radio - why is power supply reversed?
P.S. And definitely check the quiescent prior to wrapping it all up - just to ensure that those old Ge's aren't having a private party! (A properly sorted TR82 will run for months on end on a new PP9).
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29th Mar 2017, 6:56 pm | #32 | ||
Dekatron
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Re: Bush TR82 radio - why is power supply reversed?
Quote:
Quote:
5V is below the output of even a pretty well spent 9V battery (usual practice is to aim for operation down to 0.9V per cell), and if the set will work at all in that state, then you should consider it a happy accident. Running on a reduced voltage won't damage the set; but it could cause underperformance including reduced output volume, audible distortion, whistles, farting noises, loss of sensitivity and inability to tune in certain frequencies. You're basically out of the set designer's comfort zone and into the hands of the Gods. Some plug-in USB PSUs are hackable, though! You can change a resistor to adjust the output voltage. (At least, you can change it if you have a fine-tipped, thermostatically-controlled soldering iron, a steady hand and the patience of a saint!) Look for the larger of two resistors between a pin on the IC and the negative of the primary-side smoothing capacitor (the smaller one will be for setting the current). Wire in its place a suitable potentiometer, adjusting it to the same value as the original resistor to begin with; then connect a voltmeter to the output, with a 470Ω, 1W resistor as a load, adjust the pot for 9V output and finally replace with nearest preferred value. How long the smoke will stay in is anyone's guess, but it's got to be worth a punt. If all my tools and components weren't in storage pending laying a new floor after flood damage, I'd have a go myself! Be sure to change the output connector of this hacked power pack, for obvious reasons .....
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29th Mar 2017, 7:51 pm | #33 |
Dekatron
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Re: Bush TR82 radio - why is power supply reversed?
You might have success with the radio but I think it would work best with two separate power supplies, one for the radio and one for the Bluetooth unit.
Lawrence. |
29th Mar 2017, 8:36 pm | #34 | |
Dekatron
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Re: Bush TR82 radio - why is power supply reversed?
Quote:
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31st Mar 2017, 5:32 pm | #35 |
Dekatron
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Re: Bush TR82 radio - why is power supply reversed?
Re #11, in 1968 when I was a vacation student at the old STC Submarine Cables lab at North Woolwich, I was given a project to update a circuit that used PNP germanium transistors with a -ve supply rail, to use Silicon NPN transistors with a +ve supply rail.
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