Tremolo light for Gulbransen Rialto K

[pedropol]

Hello and happy new year,

I'm still trying to repair my Gulbransen Rialto K, a bit at a time... After checking all lights/resistors in the cards, today I've looked at the tremolo. According to Jan Girodot's technical book:

TREMOLO: In Model K, just ahead of the output stage, signal is drawn from the C an C# channels and varying amounts of this signal are grounded through the LDR's. The LDR's have a relatively high impedance in the absence of light and a relatively low impedance in the presence of light. Approximately seven times each second the LDR's are exposed to light for a small fraction of a second. This is controlled by a motor-driven drum that covers the exciter lamp. The drum is perforated with the holes spaced to transmit light at the required rate.

I've been able to check that the light bulb conducts electricity with a connectivity tester and I've measured 11V at the end of the wires on the card connector when setting Main Tremulant, but I've been unable to have the light bulb bright.

My questions are:
1) What are the tongues/stops that must be set to enable the tremolo? I've tried with the different tremolos stops without being able to light the bulb. Does it mean that the lamp is dead or is there another explanation?
2) How can this bulb changed? I can't find a way to remove it from the cap. Is it soldered to the wires?
3) What are the characteristics of that light? Schematics says LAMP=#1815. Is it a part number?

Thanks
--
Pierre