How A Valve Guitar Amp Works.

[Muzza]

If anybody wants to build an amp and you have no electrical experience, I would suggest you get assistance from somebody who does. There are voltages in excess of 350V dc in some of these amps, some as high as 600v I believe. (Doc, correct me if that's an exaggeration.)

I'm not sure why anybody would bother with a 12 volt / 240 volt initial input transformer, unless you want to use it for busking.

The danger of these amps isn't the 240v AC primary winding voltage, ('tho that IS lethal...) it's the high DC voltage in the circuit wiring that catches people out. Even if you had a 12 volt transformer feeding the amp, the circuit voltages would still be in the 300-400 volt range.

[DrNomis_44]

If anybody wants to build an amp and you have no electrical experience, I would suggest you get assistance from somebody who does. There are voltages in excess of 350V dc in some of these amps, some as high as 600v I believe. (Doc, correct me if that's an exaggeration.)

I'm not sure why anybody would bother with a 12 volt / 240 volt initial input transformer, unless you want to use it for busking.

The danger of these amps isn't the 240v AC primary winding voltage, ('tho that IS lethal...) it's the high DC voltage in the circuit wiring that catches people out. Even if you had a 12 volt transformer feeding the amp, the circuit voltages would still be in the 300-400 volt range.

You're actually correct, the voltages in a Valve amp can easily be anywhere from about 350 V DC to 600V DC, I have even seen one design for a 150 Watt Valve amp that had voltages as high as 750V DC which is scary to think about, and I totally agree with your safety concerns there, there is a very thin margin for errors when building a Valve amp, and the errors could prove fatal if you're not familiar with the procedures you need to follow when working on a Valve amp, I definitely would advocate getting help from someone more experienced if you're a first-time Valve amp builder.

As an example, before my Marshall MA100C amp was fixed I remember measuring voltages as high as about 600 V DC in it, the guy who fixed it managed to bring the voltage down to about 450V DC, still high enough to be very lethal though.


Our Australian 240V AC mains power that we get from the 3-pin wall sockets is actually not 240V AC, that is what's call the Root Mean Squared Voltage, in reality it is something more like about 678.9V AC, and considering that most 3-pin wall sockets are capable of supplying anything up to about 15 Amps, this makes it even more lethal.