Half-power switches on amps

[B2D]

I've got one on my Legacy to go from 100W to 50W, I've seen them on some other amps as well. How do these work?

 

[cream123]

Re: Half-power switches on amps

On my Boogie Nomad it just cuts out the outer pair of the quad.

 

[doveman]

Re: Half-power switches on amps

Same on my Mesa Boogie ... except it cuts out the two middle power tubes.

 

[B2D]

Re: Half-power switches on amps

So it removes them from the circuit but keeps power going to them?

 

[doveman]

Re: Half-power switches on amps

Yeah ... they still glow ... the heaters on. But you will notice that when you hit a chord ... only two of the four tubes "light up" ... so to speak. So the tube is basically not working the signal.

 

[LJ King]

Re: Half-power switches on amps

Yeah ... they still glow ... the heaters on. But you will notice that when you hit a chord ... only two of the four tubes "light up" ... so to speak. So the tube is basically not working the signal.

By "light up" I'm assuming you mean the "blue glow" as usually the heater supply is not disconnected (the reddish glow).

Disconnecting two of the four power tubes is normally done by disconnecting the cathode from ground.

However there are other means. For example, some Carvin amps like the x-100B series reduce the B+ or supply voltage to the phase inverter. With the reduced voltage, the phase inverter will not only distort earlier, but will also be unable to provide an adequate voltage swing to drive the output tubes to their full power.

 

[greendy123]

Re: Half-power switches on amps

I know my marshall just switches modes for the power tubes from pentode to triode for the switch. The lower settings usually have a warmer sound.

 

[Gr8Scott]

Re: Half-power switches on amps

LJKing - How does the X-100B sound when in low wattage mode as compared to the higher wattage mode?

The Traynor YCS-100 has a 30 watt switch. I think the amp goes from class B to Class A when it does this. The output gets a tad brighter and has more chime to it when in 30 watt mode. Bass lessens a touch too, but can be dialed back in.