Re: Master volume
It's true that any tube amp will sound its best loud, but that doesn't necessarily mean that they can't sound good, or good enough, at lower volumes. DSLs were certainly better at sounding good at lower master settings than the 800s were. The JVMs are better than JCM2000 DSLs at sounding good at lower volumes. There has been a progression to sounding better at lower volumes with the latest DSLs, and from many other amp companies.
Its an age old problem. First there were conventional master volumes in 70s. Next attenuators became popular. Then post phase inverter master volumes. All of these solutions worked to greater or lesser degree, but still the amp sounded better cranked. For example, a PPIMV makes the phase inverter tube distort which is part of power amp distortion and compression, but it also kills negative feedback at low settings, which usually make the amp have fizzier highs and flubby lows. It sounds good with the PPIMV turned up, but then its still pretty loud. Sometimes a combination of these volume mitigation strategies, each used in moderation, can yield better results.
EL84s to get low watts have a different sound than big bottle tubes. We are now seeing new designs of 25 watts or less master volume amps that use EL34s or 6L6s. For example, the Soldano 25 watt, the PRS Tremonti, and the Marshall mini Jubilee and Origins.....