SOOO....after I unsoldered the leads connected to the photocells, as directed to in the manual, I was able to get the photoresistors for the "Reactive" side of the bridge all set to the values listed, but the "Resistive" side of the bridge was still cranky. I went through and measured all the voltages in that section of the circuit, and they're all within tolerance per the schematic. I checked the resistors in the circuit, and they all measure within tolerance of their marked value. Everything looks "AOK", and I still can't get the photoresistor close enough to the bulb for the brightness of the bulb to lower it's value to within specs. I don't know if/how much the photresistors can drift with age, but "Bulb Aging" is a definite possibility. There's a series resistor (360 Ohms for each bulb), but I'm hesitant to lower the value, which would make the bulb brighter, and most likely shorten it's life. Hmmmm...what to do?
I was able to track down the industry part number for the bulbs used, and they're an "1869D" bulb, still available. The range in price from Nine Dollars per bulb, to Ninety Cents per bulb, depending on vendor. I bought a couple of "10 packs" from the ninety cent guy, as it turns out they use these bulbs quite a bit in various audio oscillator circuits as part of the amplitude stabilization loop, and sure enough, the same bulbs are used in one of my Heathkit Sinewave Generators. Probably a good idea to have a few spares around here...
But in the meantime, what could I do, if anything, to make what's on-the-bench get back to where it's supposed to be?
The first thing I tried was a small piece of paper behind the bulb to position it as close as I could to the photocell (yeah, I got tired of typing the whole name), and saw some improvement.
But was it the position of the bulb, or the white paper? How's about if I try and make the most of the light the bulb produces?
I cut and bent a small piece of Aluminum foil, and wedged it in, and the value of the photocell dropped to almost in range:
So for now, it looks like by changing the size and shape of the new "reflector" in there, I should be able to get this last one adjusted to be in range. And yes, I'll tack the parts down so they don't move around and affect the adjustment.
As long as it works, I'll leave it "AS-IS".....