"Keith G" wrote in message
...

"Trevor Wilson" wrote


Trevor's suggestion to get LEDs fitted is an interesting one but if the
light level is to bright I would have thought they would look hideous.
(TBH, if I couldn't fix them myself I wouldn't bother to get it done -
they don't do much other than look pretty!! ;-)

**LEDs are neat, because:

* They are available in some nice colours. Blue LEDs, particularly, offer
spectacular efficiency gains over incandescent.
* They are easily controllable, either by a simple constant current
source, or a resistor.
* There are at least three different shades of 'white' available to suit
most applications.


Last time I looked there were about 30 pages dedicated to LEDs in the
Maplins catalogue....

**Sounds about right. Just to re-iterate and to expand on some
misconceptions:

* Blue LEDs are far and away the best types to use for various reasons. They
offer about 5% of the power consumption of an incandescent lamp of about the
same light output. The reason is obvious, of course - Incandescent lamps
have pitiful output at higher frequencies (IE the blue end of the spectrum.
Lifespan of blue LEDs is pretty much infinite.

* White LEDs are not much more efficient than a decent halogen lamp. This is
in direct contradiction of many who promote LEDs as the lighting system of
the future. They do have a long lifespan, however. Figure on as much as
50,000 hours (for 50% light output). They are significantly more efficient
than the longlife lamps typically used in audio equipment, however.

* White LEDs are fundamentally different to all other LEDs. They use a blue
LED chip, with a fluorescent coating. The blue LEDs 'energises' the coating
(which is usually yellow) and the resulting output approximates white light.
Different coatings allow manufacturers to provide different types of colour
balance. VERY similar to the operating principles and colour temperatures of
fluorescent lamps. Without the efficiency of fluoros, of course. Fluoros are
still MUCH more efficient than LEDs, of course.

* Most LEDs have a very narrow angle of output. My favourites are Lumileds,
which exhibit a 120o spread of light. Perfect for backlighting those old
1970s Marantz receivers (blue dials, you see).


--
Trevor Wilson
www.rageaudio.com.au

The incandescent light bulbs in these Technics power amps are quite low level illumination. This may be seen as 'classy' it is certainly not 'pimp my ride'. The bulbs are mounted on two PCBs (parallelled) with five lamps on each board in series. The power supply to these boards is 37.3v AC, so each of the original bulbs is receiving approx 7.5v AC. LEDs may be an attractive option, indeed I find myself looking on this thread for that reason, but unless technology has moved on, note especially to Trevor Wilson, my experience of running LEDs on AC is that, although they will usually work, it dramatically reduces their expected life. So best stick in a simple 4-diode rectifier. Check the output DC voltage and calculate how many LEDs in series you will need to absorb the DC voltage measured. Paste these along the original PCB, so as not to contact any of the circuitry and not to obscure the original incandescents. Connect each end to the rectifier. For those to whom it is not 'too much work', there is a handy switch offered by Technics to switch off the meter display lights (it's a DPDT switch). Consider re-wiring this so that you can switch between your new pimped bright blue LEDs on DC and the original Technics incandescents on 37.3v AC.

The incandescent light bulbs in these Technics power amps are quite low level illumination. This may be seen as 'classy' it is certainly not 'pimp my ride'. The bulbs are mounted on two PCBs (parallelled) with five lamps on each board in series. The power supply to these boards is 37.3v AC, so each of the original bulbs is receiving approx 7.5v AC. LEDs may be an attractive option, indeed I find myself looking on this thread for that reason, but unless technology has moved on, note especially to Trevor Wilson, my experience of running LEDs on AC is that, although they will usually work, it dramatically reduces their expected life. So best stick in a simple 4-diode rectifier. Check the output DC voltage and calculate how many LEDs in series you will need to absorb the DC voltage measured. Paste these along the original PCB, so as not to contact any of the circuitry and not to obscure the original incandescents. Connect each end to the rectifier. For those to whom it is not 'too much work', there is a handy switch offered by Technics to switch off the meter display lights (it's a DPDT switch). Consider re-wiring this so that you can switch between your new pimped bright blue LEDs on DC and the original Technics incandescents on 37.3v AC.