The MC14046BCP seems to be gone. Is a Texas Instruments CD4046BE a good sub?

Yes, they are basically the same.

Both Rich Fair and I have recently used the TI chip as a sub in the synthesizer.

Only sub I've found that I have trouble with is CD74HC4046AE, which will work if the capacitor on Pins 6 & 7 is about 250pF and a 100K offset resistor is connected from Pin 12 to ground. However, output waveform contains distortion not seen using the suggested ICs.

Cool, I'll order me one from mouser.
Thanks all.

As for the leading prefix, the "CD" and the "MC1" are just the manufacturers' own in-house designations for the same product line, a practice that was started by RCA and Cunningham (eg., UX-201A & CX-301A for the same tube).

The suffix is generally package info indicating through hole, SMT etc., and temperature range. So, as long as you check that you're getting a DIP package you're okay.

For CMOS, the important difference is the presence or absence of the "HC" designation. There's quite a significant difference between the HC4xxx process and the original 4xxx process. Most notably, the HC series is much faster, but has a much narrower power supply voltage range. It maxes out at 6 volts while the original 4000 series is good up to 15V. With the HC4046 they made other internal changes too, including a third phase comparator option.

If all else fails, drop in to Radio Shack - their part number 276-4246 is a CD4046 and what I got recently.....$2.79 price tag hiding an original $1.89 price

I thought all radios shacks closed down. I guess not.

CD74HC4046AE works here on 5 volts, waveform output is near-perfect square with no obvious distortions or ringing problems. Since it is a much "faster" part than the MC chips mentioned, it is more prone to noise pickup in the filter components. Here are values I arrived at to allow full MW tuning range:

Osc:
resistor pin 11 to gnd, 10k
resistor pin 12 to gnd, 100k
cap between 6 and 7, 300p (any 250-350p should be okay, no ceramics, mica works well)

Filter:
resistor between pin 9 and 13, 10k
cap pin 9 to gnd, 0.01uf
resistor in series with cap pin 9 to gnd, 1k+10uf (10v aluminum or tantalum, + toward pin 9)

One problem on my prototype board is frequency jitter, which is present with all chips but slightly stronger using a 74HC part. Jitter is not visible on a scope but can impress a low level noise, sort of like a soft rushing sound, onto the broadcasted signal. Black85vette and I both notice it, but we both feel it is acceptably low. By swapping in a fixed ttl oscillator there is no noise, I think because much lower jitter. I believe that with better board layout PLL jitter can be reduced. 74HC parts are MUCH faster chip designs and capable of much higher output frequencies than we need for the AM band (with appropriate component values). That speed makes them more prone to stray noise pickup, and that is why I think the MC parts are a bit quieter than HC, but in my world neither PLL oscillator can beat a fixed oscillator such as an ECS, if you can live with fixed frequency.