Looking at present day valve technology as such it would not be at its perfection today without help along with the way in some instances without assistance from the semiconductor industry. Just think of silicon diodes compared with what we had to put up with in the days of the large cumbersome copper oxide rectifiers followed by the slightly more compact selenium rectifiers needing lots of space for air circulation.
About 70 years back if you needed a completely potential hum free audio input stage you had to put a clean DC supply onto the heater, and it could only be supplied by batteries, not very practical at all, or rectify the AC supply using those big metal rectifiers followed by those very large sized capacitors available then.
Enter the silicon diode, hardly any space taken together with present small capacitors, a fraction the size and the DC heater supply can be regulated exactly by using any of the host of power supply IC's now available.
A trick I have used on occasions when needing to replace a valve with a 6.3 volt heater and a replacement not been available and having a 12.6 volt equivalent on hand is to use a voltage doubler by using two diodes of the 1NXXXX series mounted on the valve socket with one small electrolytic capacitor and there you have a 12.6 volt valve running on a 6.3 volt supply.
Another concept that came about in the early 1950's was to have an entirely hum free input stage was to power the heater with RF, not sure if any commercial equipment was manufactured but for the home constructor an oscillator coil was produced by Allen Components Ltd (their coil no RF507) and used a valve such as a 6V6 or equivalent as the power oscillator consuming about 15mA at 200 volts plus of course the power by the oscillator valve heater. Not sure what the operating frequency was but would assume it would be around the same as that used by the bias oscillator for wire/tape recorders at that time.
About 70 years back if you needed a completely potential hum free audio input stage you had to put a clean DC supply onto the heater, and it could only be supplied by batteries, not very practical at all, or rectify the AC supply using those big metal rectifiers followed by those very large sized capacitors available then.
Enter the silicon diode, hardly any space taken together with present small capacitors, a fraction the size and the DC heater supply can be regulated exactly by using any of the host of power supply IC's now available.
A trick I have used on occasions when needing to replace a valve with a 6.3 volt heater and a replacement not been available and having a 12.6 volt equivalent on hand is to use a voltage doubler by using two diodes of the 1NXXXX series mounted on the valve socket with one small electrolytic capacitor and there you have a 12.6 volt valve running on a 6.3 volt supply.
Another concept that came about in the early 1950's was to have an entirely hum free input stage was to power the heater with RF, not sure if any commercial equipment was manufactured but for the home constructor an oscillator coil was produced by Allen Components Ltd (their coil no RF507) and used a valve such as a 6V6 or equivalent as the power oscillator consuming about 15mA at 200 volts plus of course the power by the oscillator valve heater. Not sure what the operating frequency was but would assume it would be around the same as that used by the bias oscillator for wire/tape recorders at that time.
