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. That's important because Low-power tube Hi-Fi amplifiers, and all guitar amplifiers, spend a lot of time in overload. 

The photo shows a very rats nested small Class AB push-pull amplifier using dual triode/pentode 6BM8 tubes to give about 8 watts RMS output. The idea is/was to fit it into the same small chassis as the Red Roo PR5 vinyl preamplifier, so they could 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 in kitsets 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.

UPDATE 1st Feb: Well, after quite a bit of listening I thought it sounded good but, compared to the SE5 Class-A amplifier, not good enough, and with only about twice the power output of the SE5 it doesn't seem worth the effort. (Twice the power is only a 3dB increase and, due to the near logarithmic response of the human ear, a worthwhile power increase needs to be at least four times, or 6dB).

Another option is an upgrade to the SE5 to give about 10 Watts output. The HT voltage would need to be increased to about 400V (which might be a bit scary for some) but again the power increase would only be marginal at about 3dB.

The other thing I would like to try is a hybrid design with Texas Instruments 'Overture' audio amps in the output stage. That is the 'sensible' way to go with solid state devices in the output stage giving about 25 watts.

Phil