I finally got around to powering up my #1222 VCOs, I was waiting for the mica caps to arrive from AliExpress but they’re still at least a couple weeks away, so I gave up.
While poking around trying to figure out why I can’t seem to be able to calibrate the frequencies (more on that later), I noticed a resistor getting quite hot.
It is R42, the resistors in series with the 4.1 voltage reference.
I did a bit of math :
The current through R42 is I=V/R= (12-4.1)/220 = 35.9mA which seems a bit high.
The power dissipated by R42 is P= VI = (12-4.1)x35.9mA = 0.28 watt which is more than the quarter watt that my resistor is spec’d for.
Again, that seemed high so I looked at the spec sheet of the LM4040AIZ to see if we could safely reduce the current.
Not only can we, but we should reduce the current as the maximum recommended current is 15mA.
So @lookmumnocomputer, I recommend replacing R42 by a 1K (or more) resistor to reduce the current to a safer 7.9mA.
The power dissipated by a 1K R42 would then be reduced to about 1/16 of a watt.