How does a tube amp work?

I didn`t want to open another thread so i just decided to ask here.
What is the difference in power between a Tube amp and a SS one, i`ve seen alot of people using tube apms 2x25 watts to power speakers that require 100watts to run properly?
 
CAUTION - TUBE AMPS CAN USE 500+ VOLTS DC POWER WHICH CAN KILL YOU. BE CAREFUL, ASK QUESTIONS FIRST.

Useful links for tube and tube amp information are located here.

Explanation of how a tube amp works is continued here and here.

What are the parts used in a simple triode (three part) vacuum tube?

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Anode – the piece of metal in a tube, also called the Plate, which is positively charged (B+ DC voltage) and to which the negatively charged electrons flow. The electrons flow out of the tube via the anode (plate) to generate an electric current. In a small signal (preamp) tube, the anode current is fed to the control grid of the power tube. In a power tube, the anode current is fed to the output transformer input winding.

Grid – also called the control grid. It is placed between the cathode and anode. The grid uses a negative bias voltage. The AC signal from your source (e.g., CD player, turntable, tuner) is applied to the grid. The grid acts like a valve inside the tube that controls the flow of electrons from the cathode to the anode. This is why vacuum tubes are also sometimes call Valves, or thermionic valves.

While we are using the water hose analogy to understand electricity, think of electrical voltage as being the pressure inside the water hose (wire), electrical current being the flow rate of water through the hose (wire) and a ball valve or nozzle on the end of the hose being an electrical component, like a resistor or rheostat in the electrical circuit, that controls the flow rate of the water through the hose (wire or circuit).

If a tube didn't have a control grid, the signal leaving the tube would be at the maximum all the time. The control grid regulates the flow of electrons from the cathode to the anode. Higher electron flow equals more amplification.

Cathode – the piece of metal in a tube that surrounds the heater, but does not touch it (an indirectly heated cathode), or is located nearest the heater. The cathode emits electrons when heated and DC power (B+ voltage) is applied. These electrons generate a current as they flow from the cathode to the anode.

Heater – the filament (piece of wire usually wrapped around a rod) that heats the cathode so the cathode can emit a cloud of electrons. Electrons are negatively charged. The heater is what you see glowing inside a vacuum tube you amp is turned on. The heater is also of course what causes the tube to be hot to the touch. Heaters typically use AC power (but can use DC power), 6.3 volts for 6DJ8 and similar tubes, 12.6 volts for 12AX7 and similar tubes.

Getter – usually a halo shaped piece of metal wire near the top of the tube, but it can also be on the side or bottom. Other shapes are also used: squares, “D” shaped, windmill, dishes, etc. The getter is coated with a highly volatile powder before being installed in the glass envelope. The getter has no effect on how a tube operates in a tube amp. After it is flashed (see Getter Flash below), it serves no purpose.

Getter flash – after the tube is built, all the air removed and sealed to create a stable vacuum in the tube, the getter is flashed by heating it and the volatile powder explodes and created the getter flash. Getter flash appears as a silvery mirror-like coating on the inside wall of the glass envelope near the getter wire. Getter flash turns powdery white or light brown as a tube ages. This is typically caused by a slight loss of vacuum in the tube and the air that leaks in reacting with the getter flash. Loss of getter flash can indicate that a tube is going bad. If the getter flash is 100% powdery white, the tube is probably bad.

Glass envelope – a glass bottle (or sometimes metal) is used so that the air inside the tube can be evacuated to create a vacuum inside the tube. A vacuum is required to keep the components inside the tube from burning up rapidly.

Base and pins – the base, usually plastic, gives the bottom of the tube and pins mechanical strength and reduces the potential that the tube will be damaged during installation and removal. Most small signal tubes(e.g., 12AX7s, 12AU7s, etc.) and some power tubes (e.g., 7868s) don’t have a plastic base. The pins are the electrical connection between the components inside the glass envelope and the tube sockets in the amp, preamp or tuner section of the tube amp.

If you want to know what each pin of any tube does, check out the Duncanamps.com searchable database: http://tdsl.duncanamps.com/tubesearch.php

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Types of vacuum tubes?
Tubes like the 12AX7, 12AU7 and 6DJ8, all commonly used in preamp sections of a tube receiver or integrated amp, are all dual triode tubes. This means they are actually two tubes in one glass envelope. Preamp tubes amplify the signal only a little bit in comparison to the amplification achieved with power tubes.

There are many other kinds of vacuum tubes. For example, a pentode power tube like the EL84/6BQ5/7189 contains all three components described above (cathode, anode, control grid), but adds two more grids (screen grid and compressor grid).

What does the Power Transformer do in a tube amp?
Transformers either step up low voltage to higher voltage or step down high voltage to lower voltage. You have a step-down transformer somewhere outside your home that reduces the high-voltage line next to your house from 440 or higher VAC (volts alternating current) to 120 or 240 VAC that is used in your home.

AC power is supplier to the power transformer and stepped up to a single higher voltage or various voltages via separate windings in the transformer. The primary winding is the power input side of the transformer, secondary winding is the output side.

Why is a rectifier needed?
Rectifiers convert AC power to pulsing DC power. The AC output of the power transformer is fed to a rectifier tube or rectifier bridge or diodes that convert the AC (alternating current) power to pulsing DC (direct current) power. The DC power pulses because only 1/2 of the sinusoidal AC power wave is converted into DC power by the rectifier. These DC power pulses are smoothed out by the power supply capacitors (see explanation below). The resultant DC power (B+) is then supplied to the anode and cathode (plates) of the tubes.

This AC to DC conversion is required because most parts in a tube amp use DC power.

What purpose do the power supply filter capacitors serve?

Great link on why old capacitors need to be replaced, and which to replace: http://www.antiqueradio.org/recap.htm

Power supply filter caps are polar electrolytics (unlike coupling caps which are non-polar film or paper-in-oil caps) and are wired in parallel (coupling caps are wired in series). The pulsing DC power from the rectifier stage is smoothed out by the power supply filter capacitors to supply consistent DC power to the tubes and other components in the amp. The diagram below shows how the amplitude of the pulses is reduced via the filter caps (and regulator if your amp has one).

One analogy is the power supply filter caps act like the springs on your car that absorb the bumps in the road (pulsing DC power from the rectifier)and deliver a smooth ride (constant DC power) to the passengers (tubes).

@GordonW further explains how power supply filter caps work in this post.

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How does a small signal tube work in a tube preamp or power amp?
Signal tubes such as 12AX7s, 12AU7s, 6DJ8s are typically used in the preamp section of an integrated amp to amplify the input source signal. You will also see small signal tubes in standalone power amps too, where they are also being used to amplify the preamp signal.

The AC signal from from the audio source (e.g., CD player, turntable) is fed to the control grid of the small signal tube and modulates the electron flow from the cathode to anode. In simple terms, the AC signal rides on top of the DC power flowing from the cathode to anode.

How does a power tube work in a tube amp?
Power tubes consist of a cathode, grid, anode, getter, heater and sometimes other types of grids. The anode from a small signal tube supplies the slightly amplified source signal to the power tube control grid, which controls the audio frequency and volume output of the amp.

Maximum # of character reach in this post. Explanation of how a tube amp works is continued here.
It's just an electron theory , no one has actually seen them !
 
The inputs connected to the pre amp , the pre amps connected to the volume , the volumes connected to the tone, the tones connected to the splitter , the splitters connected to the output tubes, the output tubes are connected to the output transformers and then they go to the speakers and then your ears and it's all powered by a AC transformer, Capacitors, rectifier, resisters and by a on off switch !. A signal chain with multiplication action or what we call amplification !
 
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I didn`t want to open another thread so i just decided to ask here.
What is the difference in power between a Tube amp and a SS one, i`ve seen alot of people using tube apms 2x25 watts to power speakers that require 100watts to run properly?

This is, mind you, a pretty gross generalization- but, generally, tube amps do have the ability to be run closer to clipping, without the histrionics that can plague solid state amps, approaching clipping.

This is, primarily, due to the fact that most tube amps use far less global feedback than solid state amps- and therefore, have much less problems with the feedback causing unwanted effects near clipping (increased higher-order harmonics, non-harmonic overtones, latch-up and the like).

So, while you might not want to ever run many solid state amps at over 50% of max output- a tube amp can frequently be run up to 90%+ of output before clipping, and still sound pretty much just as good as they do at lower volume levels. So, a smaller tube amp will do.

Also, due to the peak transient levels in music (20+dB over steady state level, in many cases)- if you're running into a situation where you're momentarily clipping the amp on a peak (which happens all the time)- a typical tube amp will generally do those momentary-clipping transients more gracefully than a typical solid state amp.

Also, consider this- a 25 watt amp is only 6dB less loud than a 100w amp. It takes 10dB to subjectively appear twice as loud, to the human ear. So, it's not like more power gets you more volume level, very quickly, either. So, if you have a 25 watt amp which you can "use" to 24 watts, vs. a 100w amp that you can only "use" up to 50- that's only 3dB difference. Not that much perceived volume difference at all...

Regards,
Gordon.
 
This is, mind you, a pretty gross generalization- but, generally, tube amps do have the ability to be run closer to clipping, without the histrionics that can plague solid state amps, approaching clipping.

This is, primarily, due to the fact that most tube amps use far less global feedback than solid state amps- and therefore, have much less problems with the feedback causing unwanted effects near clipping (increased higher-order harmonics, non-harmonic overtones, latch-up and the like).

So, while you might not want to ever run many solid state amps at over 50% of max output- a tube amp can frequently be run up to 90%+ of output before clipping, and still sound pretty much just as good as they do at lower volume levels. So, a smaller tube amp will do.

Also, due to the peak transient levels in music (20+dB over steady state level, in many cases)- if you're running into a situation where you're momentarily clipping the amp on a peak (which happens all the time)- a typical tube amp will generally do those momentary-clipping transients more gracefully than a typical solid state amp.

Also, consider this- a 25 watt amp is only 6dB less loud than a 100w amp. It takes 10dB to subjectively appear twice as loud, to the human ear. So, it's not like more power gets you more volume level, very quickly, either. So, if you have a 25 watt amp which you can "use" to 24 watts, vs. a 100w amp that you can only "use" up to 50- that's only 3dB difference. Not that much perceived volume difference at all...

Regards,
Gordon.
Interesting explanation there tube vs. transistor , lately I have worked on a few Geranium transistor Amplifier's and to me they seem to sound pretty good overall compared to most transistor Amplifier's. I'm a tube amplifier man myself but I must admit that the Geranium transistor Amplifier's don't sound that bad . I run at home a stereo 6V6 / 5U4B / 12AU7 power amp with no tone or volume at full output nfb with a mixer that controls it , My speakers can take full volume so I can turn off the EQ mixer if I want to, it sounds great both ways ! . A friend of mine James Henderson - James Audio FT.Worth TX. (RIP) built this Amplifier for me , he said I could disconnect the nfb if I wanted to if I didn't like it with it , I left it alone because it sounds great , is there any advantages to removing the nfb ? . Most Amplifier's use nfb even in guitar Amplifier's . I was wondering why I can get away with it playing up at full volume sence 90 percent is the normal ? . I had a MIG Lead 100 guitar amplifier EL 34 that put out 130 watts through a Marshall 300 watt Celeston cab , 580 plate volts and -80 bias volts , it was a hell of a lot louder than any 25 watt amplifier ! At 3 volume it could eat up any 30 watt speakers in less then 20 minutes ! But what a great sounding 20 minutes !
 
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I have a question I have been wanting to ask someone about my tube preamp and this thread is a good place. I have a Dared MC-7P tube preamp that has the following tubes:

(2) 12ax7 phono stage
(1) 12aT7 and (1) 12AX7 line output
several other tubes that I assume are for power stage

I recently bought an upgraded external phono stage that I plugged into one of line inputs. I notice that the phono quality is still changed by rolling tubes in the Dared preamp phono stage sockets. If you remove any tube from the Dared it powers off so I assume that the power goes through all the tube sockets. Does the sound also go through the phono stage sockets if it comes in through the line inputs? It would be great to take the 2 expensive Mullard 12AX7s that I currentlyhave in the Dared preamp and put them in the new phono stage but have felt like I dont understand how things are working. Any advice is appreciated!
 
I didn`t want to open another thread so i just decided to ask here.
What is the difference in power between a Tube amp and a SS one, i`ve seen alot of people using tube apms 2x25 watts to power speakers that require 100watts to run properly?
The devices aren't nearly as different as the approach. In my view, the differences are apparent at the power supply style and the clipping pattern output. Please continue to avoid using watts as a quality/relevance measure.
 
I am just thankful they do work, my solid state days are over.
It is always good to have a decent working knowledge about any equipment you own.
One thing for certain, the guy's on this forum have enough knowledge to help with any problem that may arise.:jump:
 
Yes, I'm Rob Robinette (robrob on many tube amp forums). I've been buying vintage audio gear lately and audiokarma seems to be THE source for good info. I'm in the process of picking up a Techniques SL-1610 turntable from craigslist to go with my Marantz 4400 receiver. I also have a 1979 Sansui BA-2000 I purchased new from the Camp Casey Korea BX. I recently replaced the CA-2000 preamp and matching tuner I lost many years ago.
 
What is the difference in power between a Tube amp and a SS one, I`ve seen a lot of people using tube amps 2x25 watts to power speakers that require 100 watts to run properly?

What does that even mean?
Who decides what power is needed to allow speakers to "run properly"?
 
I found this video was helpful to me:Tube Amp Grounded Heater test
This helped me, I hope it helps someone else.
 
BmWr75 Thank you for starting this thread and all of you for the helpful comments!! For someone like me just getting into tube amps this is priceless info!!
 
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