Wurlitzer 726b/146b Vibrato Enabling Issues

[TooManyKeys]

Hey everyone,
I have a 726b (spinet model of 146b), the student model counterpart of the 720b (spinet 140b). The LDR vibrato assembly is present on the amplifier which is otherwise identical to a 720b. I have carefully cut out the "umbilical cord" wiring and self/ensemble switch and used clip leads to wire up potentiometers to test the vibrato circuit but haven't been very successful so far at enabling the vibrato.
The 140b schematic specifies a 100k ohm linear taper potentiometer for vibrato depth control, though some users on the forum have had luck with 50k linear taper or 100k audio/log taper for a smoother sweep. I have tried all three, with the same result: the vibrato is only present when the pot is turned no less than to the max, and even then is very weak at best, though I can observe the bulb flashing.
Could this be a result of drifted resistors throwing off the circuit that governs the bulb? Or any other culprit?
Thanks!