BULB DETAILS (nothing visible on the bulb)

	Critical ?

Voltage    6v
Current    5A  (30 Watts)

Filament    3mm x 3mm aprox (end facing)
Filament to top of collar     35mm aprox
Collar     22mm diam (notch lined up with contacts as photo Bulb 2)

Base       P22D-A ??
Base with pins, without collar         BA15d
===================================
                  Incidental

Envelope diam       25mm
Envelope length      35mm
Frosted end (this version with the phase scope)
======================================
                  POSSIBLE REPLACEMENTS

I have some Olympus TB1 bulbs
 
Voltage    6v
Current    5A  (30 Watts)
Filament    3mm x 3mm aprox (end facing)
Base with pins, without collar         BA15d

You would need a collar from an old bulb.
These are not frosted so would be correct for the non-phase scopes.
I suspect that a lightly frosted diffuser filter placed in the path would
work as well for the phase scopes but I have not tried it.

NOT SUITABLE

Philips 13347
6v 15watt
Fillament    1.5mm x 1.5mm aprox (end facing)
Filament to top of collar     32.5mm aprox
Base     P22D-B
Collar     22mm diam (notch lined up at 90degrees to photo Bulb 2, ie pins in wrong place)

Very good artlicle on Microsytem 70 by Ian Walker in Micscape Magazine December 2009 edition.

http://www.microscopy-uk.org.uk/mag/artdec09/iw-watson70.html