Every radio today uses a crystal as its reference, hence frequency stability.
Some Pll's compensate for temperature using the uprocessor, a lookup table & a DAC. I can't think of any off the shelf units that still heat the xtal unless its an option. I found little wrong with xtal heating in the older units...other than whoever installed the xtals might not have been careful or smart enough to re-establish the physical connection between the xtal & the external heating element (usually a resistor & a thermister). Sometimes an error was made in the ordering of xtals. Some models of radio came with heaters & some of the same models didn't. You had to know which you wanted before ordering. Not only were tube type radios using heaters, back in the day, but solid state mobiles & even a few solid state Ht's did too.
