fluff191 said:
If you only pull one rectifier tube, it will double your ohms rating on your speaker outs.
For example you would have to plug your 8 ohm cab into the 4 ohm jack.
You have a 4 ohm cab, and the lowest possible rating is 8 ohms, giving you an unsafe mis-match.
In other words, you can not do it unless you have a minimum of 8 ohms rated for your cab.
Get a single recto. Stop playing with 100 watt amps.
I don't think this is necessarily true.
Pulling a rectifier tube doesn't have anything to do with the speaker load. The reason for that is to keep the same amount of sag as using all 4 tubes with both rectifier tubes. The rectifier tubes supply DC voltage to the power tubes, so if you pull 2 tubes and leave both rec tubes in place, you'll have a stiffer tone than if you pulled one rec tube due to decreased load on the rec tubes. Probably comparable to using GZ34s with all 4 tubes, but I can't verify that.
As for the cab situation, I don't think it will cause any harm to your output transformer, but may wear your tubes out quicker (but please don't go on my word, call Mesa to make sure). When you pull tubes, the plate impedance the output transformer sees gets doubled (tubes are wired in parallel, which halves the total impedance). If you pull one tube from each pair, the tube impedance now doubles. To keep the same ratio at the output transformer, you plug into the output that is
half of what your cab is (because that output is now
double what it is labeled.).
The output transformer is still going to see a 4 ohm load in this case, but the tubes are going to see half of what they should. It would be like plugging a 8 ohm cab into the 4 ohm out if using all four tubes. The frequency response will get shifted somewhat.
To put it another way, your speaker load doesn't decrease by pulling tubes. A 4 ohm load is still a 4 ohm load. The load on the tubes however is going to be less than desirable.
But again, give Mesa a call to find out for sure.
