Electronics designers use many different prototyping methods. These days, it's very likely that a new design will never actually be prototyped but rather simulated using programs such as SPICE.

For very simple circuits like tube amplifiers, I like the rats-nest method. It isn't pretty, but it's fast and effective. It is also way more reliable with tube gear as SPICE models of tubes do not simulate all their characteristics, especially those in overload conditions, and low-power tube amplifiers spend a lot of time in overload. 

This time I'm working on a small Class AB push-pull amplifier using dual triode/pentode 6BM8 tubes to give about 8 watts RMS output. I want it to fit in the same small chassis as the Red Roo PR5 vinyl preamplifier so they can be a matching pair with enough power to drive average bookshelf speakers.

The 6BM8 was developed in the 1950s for deflection oscillators/amplifiers for televisions and general-purpose audio amplification and is still available as either new old stock (NOS) or freshly manufactured by Electro Harmonix, (I don't like using tubes that are only available NOS).

So far, so good. The power output and specs look very good. The 6BM8s will need to have some negative feedback applied to get a reasonable loudspeaker damping factor, however like the SE5 power amplifier, the feedback can be switched off or varied if a higher input sensitivity is required.

Latest: It sounds really good but, at 8 Watts output, is an extra few watts and having to go to Class AB worth all the effort? The Class-A SE5 amp is hard to follow.

Next, I'm going to try a hybrid amp with a solid-state output stage and decide which one to develop into a new kit. The obvious advantage of a solid-state output stage for a Class AB amplifier is much higher power before overload and the onset of clipping, and lower cost.

Phil