Can this bulb be subbed for diodes in this (NOT Germanium) pre amp ?

[doorunrun]

Have you tested the two transistors in that circuit to make sure they're OK? There's a reason the lamp blew. It might not be from just old age.

 

[Rob Flinn]

Have you tested the two transistors in that circuit to make sure they're OK? There's a reason the lamp blew. It might not be from just old age.

The bulb was physically damaged. i.e smashed.

 

[RoadrunnerOZ]

The bulb is used as a current limiter and needs to be replaced with like kind with the same thermal resistance characteristics - a PTC that matches the curve of this would be hard to find. There is an inherent lag in the lightbulb due to filament heating time.
These bulbs are like the low wattage ones used in switches. I can get 12V 120mA Lilliput globes here for $1.35. They come in 4.5mm screw base or pigtail or like the Rafi F9 push to insert T base.
Near you maybe for 2.43£€ :
https://shop.griederbauteile.ch/product_info.php?currency=EUR&products_id=19462&language=en

 

[RoadrunnerOZ]

Thanks for the responses everyone. I do have a second working pre amp here & it says 12v 0.12A like it says in the parts list. I did measure the cold resistance earlier & I think (from memory) it was 46ohms The bulb is a similar size to an MES but with flying wires & it solders into a holder.

What diameter is the bulb? The flying wire pigtail bulbs are commonly used in scale models - 60mA 3mm. The 120mA and 150mA are usually larger - 4.5mm for LES-E5 5mm base.
The ones with bases are just the same pigtail bulbs soldered and glued into a base. If the bulb is not panel mounted, but internally mounted, you can always modify a Liliput LES-E5 or MES adding wires and mount the screw base to the existing holder. Or if using a smaller size bulb than the holder slide it in and pack it to fit. Alternatively buy a bulb holder and bulb together and replace the existing holder.
Liliput bulb:
https://www.jaycar.com.au/12v-lilliput-globes/p/SL2652

 

[Rob Flinn]

What diameter is the bulb? The flying wire pigtail bulbs are commonly used in scale models - 60mA 3mm. The 120mA and 150mA are usually larger - 4.5mm for LES-E5 5mm base.
The ones with bases are just the same pigtail bulbs soldered and glued into a base. If the bulb is not panel mounted, but internally mounted, you can always modify a Liliput LES-E5 or MES adding wires and mount the screw base to the existing holder. Or if using a smaller size bulb than the holder slide it in and pack it to fit. Alternatively buy a bulb holder and bulb together and replace the existing holder.
Liliput bulb:
https://www.jaycar.com.au/12v-lilliput-globes/p/SL2652

I'm not sure how big the bulb I am getting is. Maybe MES. The originals had flying leads which were soldered into a holder that solders onto the pcb. One way or another I will have to adapt it to fit.