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RE: How to Trace Out Tube Amp Schematics

Posted by Palustris on February 12, 2017 at 10:23:19:
It might be helpful to remember that there is a good chance that whatever circuit you are trying to figure out is a common archetype used over and over. Examples are the Williamson, Mullard 5-20, or Dynaco ST70. There are variations of these, but what is common to each of these archetypes is that they are composed of predictable stages or blocks of components that relate to each other to provide a function.

These stages can be very generic and easy to figure out and easy to draw because you can follow a schematic of the archetype. Here's an example. The Williamson amplifier is certainly one of the most popular audio circuits ever developed so it is extremely common in commercial and hobby builds.

You see below the Williamson amp is composed of five discrete blocks of components that each serve a specific purpose. Each of these five blocks of components is common to many different amplifiers, so it makes sense to learn to draw these typical blocks and expect to see them in the amp you are attempting to draw.

So, starting with the yellow we have the power supply block. Every amplifier is going to have a variation of this one here: draw it in. Pink is the output stage. Every push pull amp is going to have a variation of this. Dog puke green is generally called a "long tailed pair" or differential amplifier; it's a common gain stage in amps. Blue is the phase inverter; this one's a split load inverter. The first stage is the most common triode gain stage there is.

Draw out these stages as practice and then look at the amp for which you need the schematic and look for the power supply components: fill them in to your drawing. Check out the output stage: is it similar to the Williamson? Discover each of the discrete blocks of your amplifier and put them together. Now that you know what you are looking for and how to draw them, the job should be easier.