Well, Pete's suggestion took care of most of the problem. There is a clear increase in intensity with R508 bypassed, but it looks like I will have to take off the front panel again to see why the light around the volume control is so dim.
Wish I knew why the resistor was there in the first place. My guess is just for longer bulb life, considering the math below.
I also attached a picture of the R508 location with the resistor still in place. It's the one with the green jumper on it.
The voltage drop across the resistor is 2.4 v, and the bulbs are getting 4.2v. Current through the resistor is 1.2 amps, assuming the resistor is really 2 ohms (I haven't cut the lead yet and measured it). So, each of the 5 bulbs is drawing about 240 mA at 4.2 volts. Each bulb must be about 17.5 ohms resistance. That would work out to about 3.5 ohms for the 5 bulbs in parallel, which would give a 4.2 volt drop at 1.2 amps. So, the math is consistent.
At 6.6 volts without the resistor in place the current draw will be 1.9 amps, or 380 mA per bulb, about 50% higher. Each bulb will dissipate about 2 watts at the higher voltage rather than 1 watt with the resistor in place. GE brand 1866 equivalents are rated 2 watts, so they should be okay and match what I am measuring. I saw another brand that had lower current draw of 250 mA at 6.3 volts, so they would put less additional load on the power supply than the ones I have now. Either way, I doubt the additional 700 mA load on the 6 v rail will be a problem, and Pete's experience bears that out.
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