Actually, JC5033 bulbs can be bought for less than $1.
Looking at the bulb replacement procedure, you may want to spend a little more on the bulb to avoid doing it too often 
Peter wrote:
Looking at the bulb replacement procedure, you may want to spend a little more on the bulb to avoid doing it too often
I strongly doubt spending more would directly help ;-) But if it’s really labour-intensive, I’d look into finding a compatible LED bulb, which would be virtually eternal. Cree, Philips and Osram all make chips bright enough to replace a 35 W halogen with a single chip, the question is only about a G4 bulb that uses one. Actually, for $135 one can probably have it custom-made!
https://www.lampdirect.nl/led-lampen/led-steeklampen/led-g4-lampen may be able to help
From a purely pedantic point of view, changing the lamp to a non-specified version is altering a TSO’d product without approved data. The SN3308 also monitors lamp current draw and life used and this function may give false results if you’ve changed the lamp to a non-standard version.
The Sandel 3308 system uses a halogen bulb with a parabolic reflector and a condensing lens – just like, for example, an old Kodak Carousel 35mm slide projector.
Such a system works by putting the light source at the focus of the parabola. In the case of a G4 halogen lamp, the “light source” means the filament.
Part of the job in hand is to make sure that the filament is the right distance fore and aft, and there are marks inside the instrument to assist. The other part is to make sure the filament is the right height – which is behind the photo earlier in this thread, from Beechtalk, I believe.
Give or take a bit, any 35W halogen lamp is going to give roughly the same number of lumens. The reason there are reports on forums of unapproved lamps resulting in dim displays is not because such lamps are less bright, but because the filament is in the wrong place and the light source is diffused because it is out of focus.
The best lamp for such a system is also the one with the smallest possible point source – i.e. the smallest filament, and you’ll note that the approved lamp has quite a tight filament. LED replacements use a few leds that are spread around and are therefore highly unlikely to work effectively. There is also a control circuit used for calibrating for maximum brightness that would probably be very confused by an LED, as described by Mr Amp above.
(In case you were wondering about this unhealthy level of knowledge – part of my Master’s degree project used a transmissive LCD with a similar illumination system to the Sandel. On reflection it was quite advanced for 1982 – such is the naïvety of youth! – and is amazing how bits of seemingly useless trivia from 35 years ago turn out still to be of value)
wigglyamp wrote:
SN3308 also monitors lamp current draw
…but this function is recalibrated every time you change a lamp (see installation manual)
Alan_South wrote:
LED replacements use a few leds that are spread around and are therefore highly unlikely to work effectively.
This is exactly why I mentioned a bulb with a single LED chip.
We have light. My avionics engineer deduced the contacts on the bulb were less than ideal, and to top it off the Rheostat was backwards.
Jobs a peach.
Ultranomad wrote:
This is exactly why I mentioned a bulb with a single LED chip.
The LED chip will be a different shape and will have a different radiation pattern to a halogen filament, though, so it’s quite possible it may not give even or proper illumination levels that you’d expect from the halogen bulb. The reflector is likely designed for the shape of the light source (the filament) and its radiation pattern and may be rather suboptimal with a different shaped source (a bit like when people put aftermarket HID headlamps in a car designed for halogens without changing the reflectors and adding the self-levelling system – it just ends up dazzling other drivers while producing inadequate illumination for the driver of the car who’s using them).
Turns out it’s the transformer that’s gone in the SN3308. I could effect a repair if I could get the PN of the transformer to replace. The tech I have doing it is going to carefully remove it from the board to see if there is a PN on the reverse. The pic here shows numbers but those are just for the inductor on the transformer.
I know it’s a long shot. Does anyone have access to a manual for one?
