Valve amps 101

[realysm42]

I'm intruiged by this type of amp but I know nothing about it. I know I can google things but I'd like a single point of reference to visit, with all of the information I need, so if you'd be so kind, please can you answer some questions for me:

1. What are the different types? I've read about push-pull configurations etc, can I have some clear definitions please?

2. I've heard people comparing ss watts to valve watts (on here) and saying they're not the same is this true, or even something I should take note of?

3. Is there an inherrent valve sound? I recently read on here people saying they don't like the associtation with valves and syruppy reproduction as it's not true.

4. What is biasing?

5. Why are there so many different types of valves? Is it akin to speaker cable/interconnects? Are they all built to standard sizes? Also, what are NOS valves?

6. What do you have and why would you recommend it?

7. Do they suit a particular type of music? Or is it another cliché that they lack punch for things like Drum and bass/rock?

I'm interested to try them out just to see what all the fuss is about; I've heard a lot of good things about them.

[AndrewR]

Hi realysm42,

To address your questions below:



1. What are the different types? I've read about push-pull configurations etc, can I have some clear definitions please?


The main ones are:
Single Ended, where the valve is conducting through the entirety of the wave.
Push Pull, where each valve is conducting during their respective upper/lower half of the waveform. Push Pull is now efficient at transferring power to the output.

Push-Pull can be split via a splitter valve or interstage transformer.



2. I've heard people comparing ss watts to valve watts (on here) and saying they're not the same is this true, or even something I should take note of?


Watts are Watts, but how it clips is different.



3. Is there an inherrent valve sound? I recently read on here people saying they don't like the associtation with valves and syruppy reproduction as it's not true.


The thing about valves it that their sound changes with biasing conditions (see below). A good implementation is not syrupy and can better the flat-earth PRAT qualities of transistor amplifiers. Audio Note, Kondo and Audion are good examples.



4. What is biasing?


It is where you set the standing (quiescent) operating conditions of the amplifier. These are the currents/voltages that are running through/across the amplifier when there is no music playing. Different valves operate optimally with different cathode currents and anode-cathode voltages across them. The cathode current is set by varying its resistance and using Ohm's Law.



5. Why are there so many different types of valves? Is it akin to speaker cable/interconnects? Are they all built to standard sizes? Also, what are NOS valves?


There are many reasons. Sometimes you see duplication of valve numbers - some North American, some European and some Russian. Sometimes the Russians with copy the American valves during the cold war. Also there has been a long period of evolution of the valve, whether it is evolution of triodes or the inclusion of pentodes and tetrodes.

Many valves are there to fill a design brief, not always audio - sometimes radio and computation-based. Therefore where there was a gap, a new valve was designed.

They are built to standard socket sizes, but not always use the same pin-out (e.g. the heater arrangement on B9A socketed valves can be different). I believe there are standard glass envelopes, but are not always used.



6. What do you have and why would you recommend it?


My self-built amps, Audio Note, Audion - lots of body, timing, tunefulness to the presentation. Tron is good, but I've not heard them under ideal conditions.



7. Do they suit a particular type of music? Or is it another cliché that they lack punch for things like Drum and bass/rock?


I like anything good. Jazz, rock, electronica, blue grass, blues, classical, off-the-wall avant-guard.

Cheers,

Andrew

[realysm42]

Cheers for the answers; from them I have some more questions:

What are the pros and cons of single ended and push pull designs?

what is clipping? And if they behave differently to ss amps, how so?

With biasing, is it risky, or are there agreed/established settings for every design?

Thanks Andrew.

[realysm42]

Also, why do so few valve amps come with xlr inputs?

[daytona600]

was a solid state man for 30years , then i bought valve amps will never go back
Yes they play drum&bass / rock/techno , some designs are pre 2nd world war , but if it works don,t fix it ask any musician what he uses in his amps valves or solid state

[Patrick Dixon]

ask any musician what he uses in his amps valves or solid state

Not really a good comparison. When you are making music you choose kit to give the sound you want to make, and sometimes you want it to distort or clip. When you are replaying music you want to hear the sound the musician wanted to make, so you want to add or take away as little as possible.

[Ali Tait]

Also, why do so few valve amps come with xlr inputs?

Cost. To implement a differential (balanced) signal usually means using a transformer to do so, adding to the cost of the amp, hence it's usually only available on more expensive examples.

[The Vinyl Adventure]

I have a valve amp for sale ... One day I'm going to thread crap that info and it's going to do me a favour ;)

[AndrewR]

Cost. To implement a differential (balanced) signal usually means using a transformer to do so, adding to the cost of the amp, hence it's usually only available on more expensive examples.

Correct. Also in the home environment, balanced inputs are not needed. The only benefit of balanced input is if your cable is picking up noise/hum.

Andrew

[Ali Tait]

I note a question wasn't answered. NOS means New Old Stock - stocks of old production valves that have never been used.

[NRG]

I'd argue that a balanced input is very desirable for a phono stage! Even if its only balanced to the SUT in the case of a MC cartridge...

[jaym481]

Cheers for the answers; from them I have some more questions:

What are the pros and cons of single ended and push pull designs?

what is clipping? And if they behave differently to ss amps, how so?

With biasing, is it risky, or are there agreed/established settings for every design?

Thanks Andrew.

Clipping is when the amp is driven to distortion by what the speakers are drawing (maybe not the best terminology, but...). If a SS amp clips the distortion is unpleasant to hear, and potentially destructive (most speakers are toasted by amps with too little power, not too much). The destruction can be the speakers, through fried voice coils etc, or even the amp itself if it goes unstable.

Valve clip "softly" and do not have the same effect.

[AndrewR]

Good point, cheers Neal. I would envisage that the balanced benefits are more noticeable on a phono stage (quieter background, etc.).

Are balanced-input phono stages a rarity?

Andrew


I'd argue that a balanced input is very desirable for a phono stage! Even if its only balanced to the SUT in the case of a MC cartridge...

[NRG]

I dont know how rare or not they are TBH Andrew, a moving coil cartridge into a SUT is naturally balanced if wired correctly. IMHO it makes quite a bit of difference to the noise floor and low level detail much more so IME than any cable or RCA connector choice.

[northwest]

I note a question wasn't answered. NOS means New Old Stock - stocks of old production valves that have never been used.

But I have always been puzzled by PRAT, I know what Prat is though. Do we have a glossary anywhere?

[daytona600]

Pace Rhytmn And Timing , naim bollocks for forward and in your face

[WOStantonCS100]

...ask any musician what he uses in his amps valves or solid state

Different animals: Besides the "sound" of these classic circuits, the reason I only play valve amps (Marshall JTM45 / Marshall Super Lead 50 / Vox AC30 / Fender Twin Reverb) is because I want the amps to clip (distort) in that distinctive way that valve amps do. Eh, except the Fender. In the case of the Marshall's, especially, I'm looking for the power valves (KT66, EL34, (EL84/Vox) to go into clipping, as opposed to just overdriving the preamp's smaller "signal" valves (often 12AX7's (ecc83)). This tends to shorten the life of the valve where theoretically it should last a lot longer in a hifi amp where the valve isn't constantly hammered.

When it comes to my hifi amps, it's a 180 degree turn. I do not want valves clipping and distorting. I do not want the input signal overdriven and coming out sounding like a rock guitar. As mentioned before, this is the case with the Fender as well, where I want a "clean / undistorted" sound for the guitar.

The beauty of valves is that they do both very well if properly implemented for each purpose.

[realysm42]

Cheers for the info so far gents.

[Stratmangler]

ask any musician what he uses in his amps valves or solid state

Do not bring this forward as an argument - a guitar amplifier is a tone generator, and the criteria of its design is wayyyy different to an audio amplifier.

[daytona600]

talking about all my mates musicians & oneones a recording studio
they are prefer& use valves to SS in preamps / power / mics & they also use them in there guitar amps & also at home on there hifis

[walpurgis]

I like valves and solid state. Like most things, there can be good and not so good interpretations of each type of design. I have Class A valve and Class A transistor power amps that sound equally good (but different), I also have Tripath type amps that sound very good.

One Class AB power amplifier that is cheap to buy second hand (and new) and really sounds ridiculously good is the tiny Parasound Zamp V.3. If I have more knowledgeable friends visiting, I sometimes have this little amp running and they think I'm still using my valves until I tell them.

I also had a Denon PMA-350 SE integrated amp for a short while a few years ago and that was a powerful and very good sounding unit, so much better than I had expected it to be. Way superior to the PMA-250 SE that was all the rage in cheaper integrateds back then.