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Modifying the Bamag - Figure 1.
The example used for this project is a
projector bought on Ebay for £125. On examination, I found
that the electrical wiring was Asbestos insulated, this was
inevitably turning to dust; The brushed motor was noisy but worked
OK; Their were no switches for the lamps or power, but when
plugged in the projector worked OK.
Even with the fitted 240 volt - 750 watt lamp
it was not as bright as my own Aldous/Leitz projector using 24
volt - 150 watt lamps Figure 3., not surprising when you consider that the
earlier A1/9 lamp only uses half the current of the later FCS.
I decided that this very basic but solid
projector with its wonderful shuttered slide carrier was
definitely worth modifying. The modifications include:
Fitting a toroidal mains transformer with
240 v primary input and two 24 v secondary outputs rated at a
total 500 watts. Figure 2.
Fitting two EJS (24 v - 250 watt) lamps.
Figure 4.
Rewiring to an acceptable standard
including lamp switches, fan speed control and power connector.
Figure 5.
Replacing the primary condenser lenses to match the lamp
filament size. Figure 6.
Relocation of the polarising filters to
reduce affect of heat.
Choosing and fitting the Transformer
I chose to use a toroidal mains transformer for this project.
These can be obtained from
www.maplin.co.uk
with a 220 volt Primary
winding and two 24 volt Secondary windings - ideal for powering two
Halogen lamps. Being ambitious and considering the size of
the Bemag projector, I chose to go for 250 watt (EJS) lamps which
are readily available and cheap. Unfortunately, Maplin
didn't have a teroidal transformer with the required 500va rating
and I sourced an alternative supplier. Maplin do have 330va
unit which is part number N09BA which
costs £29. I suggest that anyone following in my footsteps takes
this route and use two 150 watt (FCS) lamps. If you prefer
the EJS lamp otion, a sutable transformer is available from
www.cse-distributors.co.uk
at a cost of around £70!.
The transformer can be fitted within the confines of the
Bemag projector base if you are prepared to modify the lamphouse.
I cut the grill off the bottom of the lamphouse to allow the transformer
to be mounted within it. The transformer is then suspended
from a bracket fitted inside and fashioned to take the
single bolt fixing of the transformer. The positioning of
the transformer is such that the clamping plate does not extend
beyond the
base of the projector.
Fitting the lampholders
The lampholders for the EJS and FCS lamps are the same - G6.5.
I purchased these from Maplin at
www.maplin.co.uk and modified the existing
lampholders to take the replacement ones, this lets the existing lamp adjustment features of the Bemag
remain functional. To carry out this aspect of the
modification, the original lampholders are inverted and the now
uppermost part is drilled to take the flying leads and fixing
screws of the new lampholder Figure 7.
The Maplin part number is KH72P and they cost £2.50 each.
Spacers are required to achieve the correct filament height, fine
adjustment being achieved by the clamping screws holding the
original lampholders in place. Axial adjustment of the lamps
is achieved in the same way.
The Electrics
The additional electrical components as seen in
Figure 5. are mounted on a
panel fixed to the rear of the lamphouse. The projctor's
cowling was cut to give access to the panel and the retaining
screw re-located. This panel is made from 6mm MDF, yes MDF!,
which is fitted with two 10 amp, single pole single throw switches
(SPST), a power connector and a fan speed control. Two holes
provide access to the lampholder adjustment screws.
The two switches are Maplin part number JK25C
and are wired between the secondary outputs of the transformer and
the lampholders. The fan speed control was obtained from B&Q
and is wired between the mains supply and fan motor; replacing the
rheostat that is now redundant. I figured that by having a
variable speed control, I could find a compromise between noise
and temperature. The rmains connector is a Euro chassis
plug, Maplin part number HL15R.
The Optics
When testing the projector, It seemed to me that although the
light output from the 250 watt lamp was an improvement over
the original 240 volt 750 watt lamp, it wasn't any better than
that achieved by the 24 volt 150 watt lamp in my home made 24 volt
150 watt powered Aldous/Leitz projector. Having bought half
a dozen scrap Kodak SV 2000 slide projectors, I removed two
primary Aspheric condenser and fitted these to the Bemag with
little modification. The light output is improved with this
single action by around 20% due to the lens's better match with
the smaller lamp filament. This may seem a bit of a let-down
if you are going to use the 150 watt FCS lamp and do not have
access to modern lenses, not so, the lower cost of halogen lamps
(£3 as opposed to £30) speaks for itself.
A final touch was to introduce my own version of polarising
filters. Those that came with the projector had faded,
proven by them not totally canceling out when laid over each
other. My solution was to extract the film polarising
filters from cheap card stereo glasses and fit them into 2"x2"
slide mounts. These were then be located in the original
glass filter holders, although these were moved closer to the
slide carrier to reduce the chance of heat damage.
A Case is required
Having now got a satisfactory Bemag stereo projector, I set about
making a case; the base of the case can be seen in
Figure 1. It is constructed
from 6mm MDF with all the fittings and covering being acquired
from Maplin. The projector remains in the base of the case
during projection.
NOTE:
I have recently
modified a later version of the Bamag projector (Sn. 701) for a
T.D.S. member. I tackled this is in a slightly different way
using a 330 watt transformer that now fitted in the lamp-house
plus, a combined lamp dimmer / on-off switch. The
independent lamp switches and motor speed control were not fitted.
(Barry Aldous - December 2005)
Modifying the FED - Figure
8.
The example projector is one purchased from Stereo Photo World at
a cost of £250 (now £350). The machine is a late production model and
has been electricaly upgraded by SPW.
Having researched the
availability of the 220 volt - 200 watt halogen lamps fitted as
standard and
comparing their performance with my Aldous/Leitz projector, I
decided to modify the projector to take the 24 volt 150 watt FCS halogen lamps. The FED comes with slide
carriers for both Realist and 2"x2" slides and so this was taken
into consideration when carrying out the modifications which
included:
Making a base unit for the transformer
Figure 13.
Fitting a taroidal mains transformer with
240 v primary input and two 24 v secondary outputs rated at a
total 330 watts
Figure 12.
Fitting two FCS (24 v - 150 watt) lamps
Figure 11.
Rewiring to an acceptable standard
including lamp switches and lamp dimmers to act as Faders
Figure 9/10.
Making the base unit
This is a housing manufactured from 12mm MDF with dimensions that
match the those of thy FED projector itself. The structure
is basically four walls with a bridging piece to carry the
teroidal transformer
Figure 12.
The transformer is positioned directly under the fan so
that air passes freely around it before entering the projector.
The grill and feet are removed from the projector and secured to
the base unit; a nut was embedded into the MDF to take the
adjustable front foot
Figure 13. I used MDF primer
to treat the surfaces of the base unit before applying a grey
Hammertone spray finish, courtesy of B&Q.
MORE TO FOLLOW
Modifying the Hawk 1 - Figure 14.
My Hawk 1 was purchased on eBay for £160 without lamps or a slide
carrier. There were also some electrical problems that
needed sorting.
I decided that before upgrading the lamps, I would buy a couple of
the standard A1/17's to see how effective they were in comparison
to my other projectors. It appears that the optics in this
projector are specifically designed for the unique integral
reflector of the lamps; changing the lamps would impose a major
overall of the optical system and power supply.
Having got the projector up and running, I was satisfied with the
light output, which was about one stop less than that of my
own Aldous/Leitz rig but the eveness of the display was poor.
I decided that I should perhaps upgrade the nprojector in two
stages.
The Phase 1 modifications I decided upon were:
Adding a fan to help air movement through the projector
Figure 15/16.
Adding a light dimmer to act as a Fader
Figure 17/18.
Introducing my own Polarisers
Figure 17/19.
Rewiring and replacing the lamp switches
and heat filters was also undertaken.
The Phase 2 modifications I decided upon were:
Replacing the lamps and condenser optics with those from two
scrap Kodak AV 2000 projectors.
Replacing the transformer with a 330 watt
toroidal.
Adding a second fan below in the base of
the projector.
Barry Aldous - January 2005
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