There is the six volume textbook answer and the two page answer to how guitar amplifier valves work.<\/p>\n
I expect you\u2019d like the shorter version!<\/p>\n
To understand the basics of guitar amplifier valves all you need to know is that \u2018like charges repel\u2019 and \u2018opposite charges attract\u2019. You probably recall that from school. So, negative repels a negative. Positive repels and positive. Negative and positive attract each other. (It\u2019s the same with magnets where like poles repel and unlike poles attract.)<\/p>\n
Armed with that fact, you can understand how guitar amplifier valves work.<\/p>\n
Here is the explanation.<\/p>\n
If you put a torch bulb filament (let\u2019s call it \u2018The Heater\u2019) under a thin piece of metal (let\u2019s call it \u2018The Cathode\u2019) then as The Cathode heats up, negatively charged electrons will \u2018boil off\u2019 by the zillion.<\/p>\n
Don\u2019t worry about how\/why unless you want a course in quantum physics thrown in for free! Left unattended the negative electrons just all repel each other, bash into HUGE air molecules and generally dissipate.<\/p>\n
Let\u2019s encase our heater and cathode in a glass tube and suck all the air out. Guitar amplifier valves have this arrangement of course. The vacuum stops the electrons smacking into these house-sized (as far as the electron is concerned) air molecules.<\/p>\n
We still don\u2019t have a guitar amplifier valve though.<\/p>\n
So at the other end of the tube we\u2019ll put another thin piece of metal (let\u2019s call it \u2018The Anode\u2019) and we will put a really high positive charge on it. In fact we\u2019ll connect it to the HT supply of around +500V. We\u2019ll connect the cathode to ground. Guitar amplifier valves are connected up like this inside your amplifier.<\/p>\n
Remember opposite charges attract? Those billions of negative electrons will now rush across the vacuum, attracted by the positive anode. In electronics speak, this is the same as saying \u2018a current flows from cathode to anode\u2019.<\/p>\n
Guitar amplifier valves rely on this current to work of course. For you interest, in an output valves, this steady state current is called the \u2018bias current\u2019.<\/p>\n
Guitar Amplifier Valves in Practice<\/p>\n
We could leave this set up operating for years and this steady bias current would just flow. We still don\u2019t have a valve though.<\/p>\n
At this point I want you imagine putting a loudspeaker between the anode and +500v. In other words \u2018in circuit\u2019 with the guitar amplifier valves. In real life the speaker is isolated by an output transformer, not least of all because you don\u2019t want 500V on one of your touchable\u00a0 speaker terminals! But for this explanation let\u2019s ignore that complication.<\/p>\n
If you\u2019ve ever tested a speaker by putting (say) a 1.5V battery across the tags you\u2019ll know the speaker cone goes out (or maybe in) and just stays there. That\u2019s because the current flows just one way of course. It\u2019s DC. If you reversed the battery, the cone would move oppositely and stay in the other position.<\/p>\n
So in our setup above, with steady state bias current flowing through the valve and through the speaker, the cone would move out (say) and just stay there.<\/p>\n
If only we could get it to go in and out rhythmically, we\u2019d have ourselves an amplifier! The guitar amplifier valves in your output stage accomplish this feat.<\/p>\n
To accomplish this sneaky trick, here\u2019s what we do. We insert a mesh of metal between the cathode and the anode. Let\u2019s call it \u2018The Grid\u2019. It\u2019s a mesh because we want lots of electrons still to be able to get through it.<\/p>\n
Guitar amplifier valves arrange for the mesh to be negative with respect to the cathode. Let\u2019s call this \u2018negative bias\u2019. Since negative repels a negative, I hope you can see that there is a certain negative grid voltage at which the electrons boiling off the cathode will be turned back by the repulsive action of this negative voltage. They would never reach the anode. When this happens in guitar amplifier valves, the valve current stops flowing (no electrons can battle through the negative grid to get to that temptingly positive anode.) The valve is OFF. Note at this point the speaker cone is just in its middle, resting position since there is no current going through it.<\/p>\n
Fine so far?<\/p>\n
Let\u2019s make the grid a bit LESS negative than this \u2018off\u2019 position so that (say) half the current flows compared to if the grid wasn\u2019t there at all. The speaker cone comes out a little and stays there. This is the correct bias point for this valve. Biasing an amp means no more than adjusting the grid voltage to give this half way idling current. The voltage is around -35V in case you are interested.<\/p>\n
In real setups the speaker does not come out and stay out like this as it is buffered by an output transformer.<\/p>\n
Okay I expect you\u2019re home and dry now and can understand how guitar amplifier valves work. If the grid voltage goes more positive (say to -30V) then more current will flow and the speaker cone will move out more.\u00a0 If the grid voltage goes more negative (say to -40V) then less current will flow and the speaker cone will move in more.<\/p>\n
So all we do is take the AC (not DC!) audio signal from the preamp (think of a sine wave) and superimpose this on top of the fixed negative bias and … the speaker will move in and out accordingly.<\/p>\n
Now I\u2019ve simplified a bit (but not much, actually) and you can go into this more deeply if you want, but those are the basics, so now you know!<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"
There is the six volume textbook answer and the two page answer to how guitar amplifier valves work. I expect you\u2019d like the shorter version! To understand the basics of guitar amplifier valves all you need to know is that \u2018like charges repel\u2019 and \u2018opposite charges attract\u2019. You probably recall that from school. So, negative… Read more<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-72","post","type-post","status-publish","format-standard","hentry","category-stuarts-workshop-wisdom"],"_links":{"self":[{"href":"https:\/\/www.fixguitaramps.co.uk\/blog\/wp-json\/wp\/v2\/posts\/72","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.fixguitaramps.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.fixguitaramps.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.fixguitaramps.co.uk\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.fixguitaramps.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=72"}],"version-history":[{"count":1,"href":"https:\/\/www.fixguitaramps.co.uk\/blog\/wp-json\/wp\/v2\/posts\/72\/revisions"}],"predecessor-version":[{"id":73,"href":"https:\/\/www.fixguitaramps.co.uk\/blog\/wp-json\/wp\/v2\/posts\/72\/revisions\/73"}],"wp:attachment":[{"href":"https:\/\/www.fixguitaramps.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=72"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.fixguitaramps.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=72"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.fixguitaramps.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=72"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}