phyrexia
Well-known member
MusicManJP6 said:More details on this please?phyrexia said:45 and 10 will sound better through the 4 ohm output.
There are maths involved...
http://forum.metroamp.com/viewtopic.php?f=4&t=31706&start=4
On top of that, when you take two tubes out of the circuit you need to be doubling your load (i.e. running a 16 ohm cab with the amp set for 8 ohms). It's the doubling of the load that puts you in 1/2 power mode. Pulling the tubes out of the circuit just eliminates the 2nd current path that would normally be required with 1/2 the load.
would the double load issue not just tie into reflected impeadence within the output transformer instead of an actuall power cut?
That's exactly what cuts the power in 1/2...doubling the load impedance. Double the load impedance = power supply can only pull 1/2 the current through it = 1/2 the power output.
It's not the pulling of the tubes that cuts the power, although that is part of it. It's mostly the doubling of the load impedance that cuts the power in 1/2. But since you're now only pulling 1/2 the current through the load (i.e. the OT primary), you only need 1/2 the tubes.
The reason 100 watters need double the tube count is because the load impedance of the OT primary is 1/2 that of a 50 watt, which allows the power supply to pull double the current through it at max power out. But one pair of tubes alone cannot pass double the current without over-dissipating so two more are added in parallel so that each is sharing 1/2 the total current.
If you just pull two tubes out without doubling the load impedance, at max power out the power supply will try to pull double the current through them because the load has not been doubled and the tubes will over-dissipate because they simply cannot handle passing double the current by themselves.
It's the OT primary load impedance and the power supply voltage that determine the power output...not the amount of power tubes you have in the amp. The amount of current the tubes will be expected to handle along with the plate dissipation rating of a given tube will determine the required tube count to pass that load current. The tubes don't make the power...they just control the load current required for the load to dissipate the max power. The load impedance controls how much current will be required to produce the rated power output at a given supply voltage.
I thought it mentioned it in the manual for the MKV as well. 45w mode definitely sounds better from 4ohm output -> 8ohm speakercab. I ran my amp with just two EL34s and the recto tube for a couple months this way.
I don't really use the 10w mode for heavy distortion. I mess around with it in the churchband sometime, and I use it for clean at home, but there is definitely still a sonic difference between the 4 and 8 ohm output at 10w.
in fact i think it sounds better at 90w at low volume a lot of times. But I am too lazy to change the output impedance every time, also. There is not much of a sonic change in the amp when you go from 90 to 45 *while* changing the output impedance.
Not changing the impedance when changing power mode (That is - the impedance mismatch) is one of the things that changes the 'tone' of the amp when you switch power modes.
Try it, you'll like it!