Multi-Watt/Half Power switches and Impedance

[Companydamned]

I’m curious about something. Back before the days of half-power/multi watt switches, people used to simply remove two power tubes (on a hundred watter) to drop the power to 50w. Thing is, it was pretty widely recommended to change your cab impedance (eq. switching to 4ohm setting when running an 8ohm cab) to ensure safe conditions for the amp.
I have a ‘13 multi-watt Dual Rectifier, and got to thinking - the “100w/50w” switches simply shut off two of the output tubes, according to the manual. This would in theory introduce the same impedance mismatch into the equation as pulling two tubes (and not in the “safe mismatch” direction) yet there is no mention of correcting this in the manual. I emailed boogie about it, thinking maybe it is handled internally or something. This is not the case, and they more or less said that it is not necessary to make any impedance corrections when switching down to 50w, although I could experiment with the correction to see which way I like the tone and feel of better.
I guess my question is, they show a mismatch of a 16ohm impedance setting with an 8ohm cab as an "unsafe mismatch", yet when using their own multi-watt feature and dropping to half-power, this is exactly what is happening, unless I’m way off base. I’m assuming they wouldn’t put the switch right on the front panel and have no mention of this in their manual if they expected people to swap the speaker cable around. Furthermore, the fact that each individual channel has its own half-power switch so that power settings can be mixed and matched between channels, goes to show that they don't expect people to make impedance changes when using half power, as nobody is going to change the speaker cable around every time they change channels.
Are boogie tranny’s just so overbuilt that hey can handle the abuse? Could this lead to issues down the road if the amp is always used on the 50w setting, or otherwise speed up wear and tear? By all accounts, boogie doesn’t seem to think so. What say you?

 

[311boogieman]

Can't speak to the Multiwatt feature but it is fairly well known that most Boogie amps can handle a mismatch in either direction without damage to the amp. It may wear on tubes slightly more. So if I had to guess, there are no hidden switches or circuits doing that Independence drop for you when you switch to 50w.

(most decent amps can actually handle this situation too I just don't want to be the guy to say it)

 

[mnemonic]

Before the multiwatts were I thing, I’m pretty sure the manual for the 3 channel rectos recommended experimenting with an impedence mismatch to see if you like the tone more.

Maybe if they’re now saying mismatches are ‘unsafe’ it’s to discourage people from mismatching their cab, and then using the 50w mode, thus potentially mismatching even further.

 

[petee]

Your overthinking it, Mesa makes good stuff and stands behind it. If they designed it to work a certain way, I'm sure it'll be fine long term.

 

[cardinal]

I thought I read something that Mesa's multiwatt disables something--but not everything--happening at certain output tubes. So for purposes of impedance, the transformer and speakers still think that all the tubes are still in the load, but the tubes are not actually contributing to the output. But now I can't find where I read that.

Maybe Mesa somehow is powering up all the tube plates but not the grids? I'm not well versed in how this stuff works, but I think if the plates are powered up, then the tube is "active," but if there's nothing happening on the grid, then the tube isn't actually amplifying anything? That's just me guessing with limited knowledge, though.