[Amps] Amp Designs

[Garry]

Good Morning,

Is there a list of improvements that the multitude of knowledgeable 
experts on this reflector feel would benefit the older amps that use 
3-500's such as the L-4B and other similar amps of that generation? I 
know step-start is common place now and I have seen variations of bias 
methods to lower idle tube current. Years ago, RF actuated electronic 
bias circuits were popular but I don't see them today. I don't see Zener 
diodes used in bias circuits either.

I've been off the air for 16 years and got back on about a year ago.

Thanks,
Gary