[Premium-Rx] lamp replacement

[jlgrrsn at charter.net]

> 
> From: "Ahmet Gundes" <ahmet-m at usa.com>
> Date: 2005/03/01 Tue PM 11:37:38 GMT
> To: Dave <dave at voceinc.com>,  premium-rx at ml.skirrow.org
> Subject: Re: [Premium-Rx] lamp replacement
> 
> It would be possible to control the current flow thru LEDs by
> using a high power transistor ( TO-220 case is one example )
> with the LEDs connected in series with the Emitter of the
> transistor. Then connecto a Potentiometer to the base of the
> transistor to control the current into the base which in turn
> will regulate/control the Emitter current ( Ic=BxIb ).  Especially
> white LEDs are current driven and adjusting the current flow 
> thru the LEDs will control their brightness. 
> In this case LEDs need to be connected in Parallel as a cluster and this then gets connected between the Emitter and the ground.  If there is a lot of LEDs then more than one transistor might be used to better handle higher current drawn.  
> Series resistors used with white LEDs do not give good results and
> they will get very hot or burn out due to high current.
> 
> Regards,
> A. Gundes
> 
> > 
> > Don't do what I did...  I replaced the lamps with surface mount 
> > white LED strings mounted on edge (so as to shine into the acrylic) 
> > with a surface mount resistor for each string.  I used a good 
> > amount of these LEDs but still was way under the current drawn by 
> > the lamps.
> > 
> > Here's where the fun begins... The first time I turned it on, I was 
> > nearly blinded by the amount of light coming from the LCDs.  The 
> > radio is impossible to use right now unless you're wearing welding 
> > goggles.  I'll try to post a photo since it's pretty funny now.
> > 
> > I'll need to put a series resistor in the 15V line to the PCB so 
> > the receiver will become usable.
> > 
> > /Dave
> > 
> > > Jim Garrison wrote:
> > >
> > >> How easy?/How difficult?, and How cheap/How expensive?
> > >>
> > > If you are talking about leds which are found in the later version, they
> > > should not ever need replacement. If you are talking about the
> > > incandescent filament bulbs found in the early version then some or all
> > > will almost certainly have died by now...
> > >
> > > You can buy a replacement led board kit for the old version, I'd guess
> > > around $50, and this is fairly easy to install in the old version, but
> > > may require some machining of the acrylic spacer round the windows for
> > > the leds to fit.  I have found it easier to fit little surface mount
> > > leds (side firing yellow ones by Panasonic) on 1/8th inch wide strips of
> > > pcb board material, after removing the bulbs from the board.  They are
> > > connected in series in groups of 4, each fed with a 180 Ohm R.  8 above
> > > and 8 below each display.  Little slots are cut in the pcb material
> > > under each led.   The original tracks are used as supply busses and the
> > > strips can be glued, but also are held in place by the Rs and the ground
> > > returns.
> > >
> > > I got the leds from digikey, buy a few extra, as they have a habit of
> > > jumping away and getting lost...  This is actually more complicated to
> > > describe than to do.
> > >
> > > I have also fitted led lighting to one of my RA1792s, using a similar
> > > approach, a big improvement over the original which had no lighting...
> > >
> > > Good luck,
> > > Dan
> > > ac6ao / g3ncr
> > 
> > 
> 
> 
> -- 
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> Thanks to all for the suggestions! I am an artist by profession, so I may lack the proclivity for technical matters which most of you command. I think I'll do some breadboarding experiments before diving into the radio right away. You are a very generous and patient bunch! 73's, Jim