For the uneducated amongst us - Class A, B, A/B means what?

Sassafras

Given a choice between cannabis and cocaine, I'll always go for the Class A stuff.

clarkefan

What's a "single ended amp"?  I assume it doesn't refer to single channel. Everyone's throwing the expression around like it's a generally known thing.

Grunfeld

ecc83 said:

As our esteemed JPFA has said there are very, very few guitar amplifiers that are truly class A and even those that technically are would cease to be so when overdriven, a very likely scenario for a guitar amplifier! What they really mean is Cathode Biased which means the output valves draw around their maximum allowed anode current all the time, in fact when driven hard such stages actually draw slightly LESS current!

Class A (push pull, at least 2 OP valves) was/is used for high fidelity because it produces virtually no "Crossover Distortion" (mind you, I am old enough to know that peeps did not care a ***t about that until transistor amps arrived!) But even so called CA valve amps (Google Mullard 5-20) were in fact class AB which means a fair amount of current always flowed in the valves. By definition of course, hi fi amps are not run into distortion.

The bigger, past 30W say gitamps tend to be class AB but Fixed Biased. This allows the standing current to be even lower than an AB cathode biased amp giving less heat [I know what heat is! Go me!] and greater efficiency. There will be some crossover distortion but players with 50W+ amps are generally not interested in the niceties of their amps at 100 milliwatts!

But, biasing, loading, "classes" is a huge, interrelated subject and without SOME knowledge, Ohm's Law as a very basic starter, you will soon get lost.

Dave.

I highlighted all the bits where I got lost!
I was initially interested in @hubobulous 's question but I've discovered enough now to know it can't be explained in a non-technical way. 
Which is okay.

ICBM

clarkefan said:

What's a "single ended amp"?  I assume it doesn't refer to single channel. Everyone's throwing the expression around like it's a generally known thing.

Single ended means there is only one valve* in the power section, as opposed to a push-pull which has two (or an even number, in pairs) which are arranged so that they're working in opposite directions at the same time, one "pushing" and the other "pulling", which has advantages for efficiency among other things - you get double the voltage and current swing from the same pair of valves, hum in the power section is automatically cancelled so you can use less filtering, and the output transformer can be smaller because it doesn't have as large a static magnetic field. Single-ended needs more filtering to cancel hum, and larger transformers to support the static magnetic field caused by the constant current, so they're only usually found in low-powered amps where those things aren't as expensive to do.

*There are some rare amps called 'parallel single ended' which have more than one power valve, but *not* working in push-pull. This is rare because it doesn't have the efficiency advantages of push-pull, but still needs larger and more expensive transformers and filtering, so is normally a bad idea. The only ones I know of are an old low-end Gibson amp from the 1950s, the THD Bivalve, and the Laney Lionhearts.

ToneControl

ICBM said:

clarkefan said:

What's a "single ended amp"?  I assume it doesn't refer to single channel. Everyone's throwing the expression around like it's a generally known thing.

Single ended means there is only one valve* in the power section, as opposed to a push-pull which has two (or an even number, in pairs) which are arranged so that they're working in opposite directions at the same time, one "pushing" and the other "pulling", which has advantages for efficiency among other things - you get double the voltage and current swing from the same pair of valves, hum in the power section is automatically cancelled so you can use less filtering, and the output transformer can be smaller because it doesn't have as large a static magnetic field. Single-ended needs more filtering to cancel hum, and larger transformers to support the static magnetic field caused by the constant current, so they're only usually found in low-powered amps where those things aren't as expensive to do.

*There are some rare amps called 'parallel single ended' which have more than one power valve, but *not* working in push-pull. This is rare because it doesn't have the efficiency advantages of push-pull, but still needs larger and more expensive transformers and filtering, so is normally a bad idea. The only ones I know of are an old low-end Gibson amp from the 1950s, the THD Bivalve, and the Laney Lionhearts.

Victoria Regal 2

Moe_Zambeek

Audio Kitchen too - their Big chopper is 4xEL-84 running parallel single ended. My 17watt combo is a single KT88 running single ended, with some beefy trannies; The Big Trees is a single EL-84.

crunchman

ICBM said:

clarkefan said:

What's a "single ended amp"?  I assume it doesn't refer to single channel. Everyone's throwing the expression around like it's a generally known thing.

Single ended means there is only one valve* in the power section, as opposed to a push-pull which has two (or an even number, in pairs) which are arranged so that they're working in opposite directions at the same time, one "pushing" and the other "pulling", which has advantages for efficiency among other things - you get double the voltage and current swing from the same pair of valves, hum in the power section is automatically cancelled so you can use less filtering, and the output transformer can be smaller because it doesn't have as large a static magnetic field. Single-ended needs more filtering to cancel hum, and larger transformers to support the static magnetic field caused by the constant current, so they're only usually found in low-powered amps where those things aren't as expensive to do.

*There are some rare amps called 'parallel single ended' which have more than one power valve, but *not* working in push-pull. This is rare because it doesn't have the efficiency advantages of push-pull, but still needs larger and more expensive transformers and filtering, so is normally a bad idea. The only ones I know of are an old low-end Gibson amp from the 1950s, the THD Bivalve, and the Laney Lionhearts.

I'm sure that @ICBM knows this already but there are a handle of amps with a single power valve that are push pull.  The Blackstar HT5 is the obvious example with its 12BH7 valve which is a dual triode - essentially two valves in one bottle.

Any amp with only one of any of the conventional guitar amp power valves (EL84, EL34, 6L6, 6V6, KT66, KT88) would always be single ended.

ICBM

crunchman said:

I'm sure that @ICBM knows this already but there are a handle of amps with a single power valve that are push pull.  The Blackstar HT5 is the obvious example with its 12BH7 valve which is a dual triode - essentially two valves in one bottle.

Cheat .

Yes, you're right - they do have one 'power valve', as do the Marshall 1W amps too, which use a 12AU7 in push-pull like the Blackstar HT-1… but only because they're two valves in the same bottle.

For what it's worth these are the only application I can think of where the 'balanced triodes' you can pay extra for from some of the valve resellers are actually useful, because they're then effectively a matched pair of power valves.

Sporky

Classes E, F and G are where it gets entertaining.

Personally I'm a Class D sort of chap; it has the least cork-smell to it.

jpfamps

I've seen a discussion of a class G valve amp.

Not sure there has been a working example.

Sporky

Blimey. That'd be some work. I can understand g/h in big power amps, not sure it's worth it at guitar amp wattages.

clarkefan

Wow, @ICBM, thanks a lot mate, you've explained a lot there, cheers!

jpfamps

Sporky said:

Blimey. That'd be some work. I can understand g/h in big power amps, not sure it's worth it at guitar amp wattages.

The idea was to switch to a higher rail for the valve when needed using FETs, however the switching circuit looked complicated to say the least.

Not sure if this would be classed as class G as you are switching the rail voltages. Maybe it's more class H....