interesting article
 

Just found a interesting article on how to convert 01a tubes to solid state. Only drawback is "plate voltage" is 18 volts compared to 90 volts originally supplied. So all tubes in a set would have to be done, and feed it 18 volts instead of the normal 90.
My question: is there a small solid state component that will take 90 volts and drop it to 18? Or a component that could be tied in under the tube socket to drop the voltage?
http://www.greenhillsgf.com/Project_SS-Tubes.htm

There is no shortage of devices to do the job. If it were me, I'd use a power zener diode of about 47 Volts in series with an 18 Volt regulator chip, the 7818. How much current do you need?

1-10mA

why not just use an 18V power supply in the first place? With two 9 volt transistor radio batteries in series you could run it long enough to get bored.

Don't forget any linear regulator bringing 90 volts down to 18 will waste 80% of
the power consumed as heat. A honest-to-goodness ss substitute for tubes will
use fairely high voltage FETs or other devices to emulate tube performance
correctly. Regards.