Quote:
Originally Posted by Bob Ross  Right, but what's going on in the power amp section when you step on the channel-select footswitch that allows it to go from a true 10 watts rms to 90 watts rms? Usually that involves disabling some tubes (at the very least), no? I'm trying to figure out how MESA/Boogie gets around risking high voltages arcing over relay contacts, or else non-instantaneous power output changes. |
here is the text that the link was posted a bit back
they have been doing this for a while now and the roadkings had a similar layout only you could select the actual tubes you wanted individually for each channel on the output side 4-6l6's and 2-el34's and how many of them used together.
POWER: MULTI-WATT™
The bottom 3 position mini toggle in each Channel (lower left corner) is the MULTI-WATT™ Power feature that determines the amount (wattage) and type (configuration) of power each preamp Channel will be coupled with to create a classic sound. Any amplifier’s sound is 50% preamp and 50% power, so this switch is responsible for a large part of a given Channel’s personality and feel. The choices repeat for all 3 Channels and they are 90 W, 45, and 10 W. Using the switch is simple… just select the power you want for each Channel, keeping in mind that the greatest headroom, focus and authority will always be found in the 90 watt position. That’s how to use it, but for those who want the full story, here it is.
Since 1981 Simul-Class™ Power has been the heart and soul of the MARK Series amplifiers, imparting its sweet, musical character onto any sound in the vast library of the now classic MARK legacy. Cleans that shimmer with transparent layers of sweet delicate highs, while the bottom end breathes a warm fundamental under a bed of rich low mid ambience. Never harsh - always fat, the Simul lead tone is the quintessential single-note solo sound that is best described with a human trait…vocal.
This patented way of wiring an output section with two (or more) pair of output tubes combines two different styles of wiring configurations to arrive at a blend that showcases the best attributes of both.
In Simul-Class™, one pair of output tubes is wired in the more efficient, cooler running CLASS A/B PENTODE configuration, which produces the greater portion of power and headroom while running cooler. This was the popular way of wiring amplifiers from about the early ‘60’s forward - chosen for its efficient use of tubes, greater power and reliability (recently a quest for the sweetest low-watt circuits triggered a resurgence of amps wired in CLASS A). The only sonic penalty for its greater power (Class A/B Pentode wiring) is that it can have a tendency to bring forward the harsher odd-order harmonic content. The Simul solution; add a pair of tubes running in the less efficient, but infinitely sweeter CLASS A TRIODE configuration. This style of wiring produces far less power out of a pair of tubes while creating more heat, but it emphasizes the even- order sweeter harmonics and transitions to clip with a soft, rich purring quality like no other.
The MARK 5 presents you with two ways to utilize this power. 90 WATTS combines the two wiring styles to deliver the maximum power and headroom. It is substantially sweeter and warmer, and is little more scooped than a standard 100 Watt amp, yet with plenty of punch and authority. 45 WATTS shuts down the middle pair of output tubes wired in CLASS AB and allows you to operate the output section in just the CLASS A mode for a perfect lower wattage range that clips sweeter and earlier, and yet is still plenty powerful enough to play out in medium sized venues.
Combining these two opposite styles of wiring in one amplifier gives you the best of vintage and modern amplifier styles. Headroom and power are there when you need it… but there is always a naturally pleasing and musically curvaceous quality to the sound that is magic to your ears and to your hands. Simul feels great and is inspiring to play!
And finally, the MULTI-WATT™ feature allows you to switch down to 10 watts of pure CLASS A TRIODE wired in a Single-Ended configuration. This is the ultimate low wattage output section that captures the essence of the best vintage circuits. Here, the 2nd Harmonic (an octave above the note played) is allowed to pass freely through the circuit, putting a magical halo around the notes that shines and rings with beyond-vintage soul.
These three power choices give you ultimate flexibility as to the styles and venues the MARK 5 can adapt to instantly and in fact, it’s like having three separate amps in one case - each having the perfect amount of power for a different application. And when you combine the power of the separate PREAMP Channels, the combinations of EQ and the POWER options, you have the most comprehensive collection of tube amplifiers ever brought together in one chassis. That’s a bold statement; but after you spend some time exploring the combinations we’re sure you’ll feel the same.