No, it is not simple z-adamson. Believe what you like, but please don't try to influence others in areas which you, admittedly, do not understand.
One example...
Again, I am not an expert.
VAS transistor will have a Miller cap (aka Cdom or dominant pole compensation) across the B and C legs. z-adamson, do you know what a Miller cap is? VAS? As I understand it, the Miller cap compensates for, or dominates, capacitance in one of the junctions of the VAS transistor, but it directly affects the entire bandwidth as well as the stability of an amp. It is small value, usually ceramic cap, seldom if ever replaced in a recap, generally disregarded and ignored. But its role is critical. The value of the Miller cap is chosen to balance between amplifier stability and overall frequency response and/or distortion. Too large or too small of value on the Miller cap will have negative implications. Sorry, I do not understand it well enough to describe all of the implications. But to give you an idea of the level of complexity involved, and importance of this cap, here is a quote from Bob Cordell's book:
"Miller compensation uses local feedback to roll-off high-frequency response of the amplifier. The gain that is 'thrown away' acts to linearize the VAS with shunt feedback. ......It stabilizes the global negative feedback loop by rolling off the high frequency gain of the amplifier so that the gain around the feedback loop falls below unity before enough phase lag builds up to cause instability."
Yeah. Way above my head. But I do get that what is being described here is critical to proper amp function, and that a balance is necessary which is achieved by choosing the correct Cdom value based on whatever VAS transistor is being used.
The thing is, that proper Miller cap value is dependent on the Cob of the VAS cap.
The thing is, that transistor substitution lists never mention Cob. I believe that a transistor with a different Cob subbed into the VAS position, without regard to the Miller cap value, could potentially lead to issues, and such issues may not be something that would be readily apparent without proper test equipment and procedures.
The thing is, the transistor substitution lists also do not take into consideration a transistor's position or circuit function. Depending on the role(s) of a transistor in a circuit, different parameters become more significant. Transistor X may sub OK for transistor Y in some cases, but not others.
The thing is, that in the schematics for some of the amps that I have worked on, lots of transistors other than the VAS also have Miller caps. Their function I do not know. But I do assume that the value of those Miller caps was based on the Cob of whatever transistors they are tied to. And again, Cob is not mentioned in the substitution lists.
So anyway, what is written above is just ONE example of why it is my belief that transistor shotgunning is not a good policy, and why I view (and use, when necessary) the substitution lists with extreme caution. I have little doubt that there are other potential issues involved in wholesale replacement of transistors. Transistors that were originally chosen, very carefully, by someone with much greater knowledge than myself and 99% of the people who post in audio forums, to be a part of a highly complex system with intricate inter-dependencies....
Bottom line, if one does not understand potential implications of an action, then do not take that action if it is not necessary.
