20-07-2011, 01:37 PM
In other posts, I've mentioned that though I've restored many DAC90As and have a few, I don't personally find them attractive, though at least they have the merit of being so commonplace that they're affordable for anyone who likes Bakelite radios. I guess that just about everything that can be said about them has been said, many times over, so I did hesitated in writing this threrad.
I don’t fall into the camp of ‘purists’ who believe that old radios which have shortcomings, (of which the DAC90A has several noted ones), ought not to be modified, and who beleive that originality should trump functionality every time. If that’s to be the case, then we might as well just treat the radio as a non-functioning bit of history for display only, and leave it completely alone.
I’ve always held the view that safety is the top priority, and have never hesitated to upgrade safety shortcomings – for example, removing the ghastly 2-pin plug on the rear of the DAC90A and wiring a new mains lead to the set with the correct polarity, which really, is how it should have left the factory. Others may take the oppsite view, and scour e-bay for a much desired DAC90A 2-pin socket and pay a lot of money to get one. It’s a personal choice, and I wouldn’t dictate to others as to how they go about their hobby.
So, this topic is about how to improve the dim dial lights – not about whether we should, or should not, make modifications to our own property, so please let’s not go down that track.
In any event, the DAC90A is such a commonplace radio, that making modifications to improve its functionality is something I wouldn’t hesitate doing, and in that regard, the dim dial lights are high on the list. There are a number of ways of overcoming the dim dial light feature of the DAC90A – for example, one professional restorer fits a small 6V transformer to enable a pair of easily obtainable 6V MES bulbs to be run in parallel, and I know that others – Joe (Pillenwerfer), and I think Rob (Bushbaby) have mentioned the use of LEDs, perhaps mounted in MES bulb bases to be screwed into the DAC90A bulb-holders. However, there are two issues here on which I’d be interested to receive any feedback – firstly, that the LEDs need a series resistor, and secondly, that LEDs are designed to work only in a forward conduction mode, so can easily be damaged if subjected to reverse voltage. They usually have a reverse voltage of 5 Volts or less, so can be damaged by accidental reversed connections.
Thus, LEDs are designed to work on a DC supply, so if needed to operate from an AC supply in which the voltage reverses with each cycle, LEDs need some form of protection, the simplest of which is to fit a silicon diode (eg, 1N4001) across the LED to limit the reverse voltage to the LED on the negative-going half cycle to 0.6V. Though this protects the LED, it does mean that no light will be emitted from the LED in the negative half cycle on the AC waveform, even though current is being drawn. Although the light will be steady, it will be half the intensity. A better way to do this if desired to work the LED on AC is to fit it across a diode bridge. I've attached a rough sketch to make this a little clearer. (I hope!).
I wonder how those who've modified the DAC90A to use LEDs rather than MES 3.15V 0.15 A bulbs have gone about it? Maybe a series 1N4001 to rectify the AC to DC, then a series resistor, with a pair of LEDs in parallel?
Just interested.
Any comments guys?
David
I don’t fall into the camp of ‘purists’ who believe that old radios which have shortcomings, (of which the DAC90A has several noted ones), ought not to be modified, and who beleive that originality should trump functionality every time. If that’s to be the case, then we might as well just treat the radio as a non-functioning bit of history for display only, and leave it completely alone.
I’ve always held the view that safety is the top priority, and have never hesitated to upgrade safety shortcomings – for example, removing the ghastly 2-pin plug on the rear of the DAC90A and wiring a new mains lead to the set with the correct polarity, which really, is how it should have left the factory. Others may take the oppsite view, and scour e-bay for a much desired DAC90A 2-pin socket and pay a lot of money to get one. It’s a personal choice, and I wouldn’t dictate to others as to how they go about their hobby.
So, this topic is about how to improve the dim dial lights – not about whether we should, or should not, make modifications to our own property, so please let’s not go down that track.
In any event, the DAC90A is such a commonplace radio, that making modifications to improve its functionality is something I wouldn’t hesitate doing, and in that regard, the dim dial lights are high on the list. There are a number of ways of overcoming the dim dial light feature of the DAC90A – for example, one professional restorer fits a small 6V transformer to enable a pair of easily obtainable 6V MES bulbs to be run in parallel, and I know that others – Joe (Pillenwerfer), and I think Rob (Bushbaby) have mentioned the use of LEDs, perhaps mounted in MES bulb bases to be screwed into the DAC90A bulb-holders. However, there are two issues here on which I’d be interested to receive any feedback – firstly, that the LEDs need a series resistor, and secondly, that LEDs are designed to work only in a forward conduction mode, so can easily be damaged if subjected to reverse voltage. They usually have a reverse voltage of 5 Volts or less, so can be damaged by accidental reversed connections.
Thus, LEDs are designed to work on a DC supply, so if needed to operate from an AC supply in which the voltage reverses with each cycle, LEDs need some form of protection, the simplest of which is to fit a silicon diode (eg, 1N4001) across the LED to limit the reverse voltage to the LED on the negative-going half cycle to 0.6V. Though this protects the LED, it does mean that no light will be emitted from the LED in the negative half cycle on the AC waveform, even though current is being drawn. Although the light will be steady, it will be half the intensity. A better way to do this if desired to work the LED on AC is to fit it across a diode bridge. I've attached a rough sketch to make this a little clearer. (I hope!).
I wonder how those who've modified the DAC90A to use LEDs rather than MES 3.15V 0.15 A bulbs have gone about it? Maybe a series 1N4001 to rectify the AC to DC, then a series resistor, with a pair of LEDs in parallel?
Just interested.
Any comments guys?
David
