I am wanting to build myself a 120w quad el34 valve guitar amp, i was just wondering if there are any simple amp circuits out there, i was going to build a transistor amp, but decided i wanted the sound from valves, im not too worried about adding distortion/overdrive, as i have an effects pedal, but i want it to be good for vocal as well, and thats where valves come in for that crystal clear sound i was also thinking about using a preamp with 12AX7 valves.

Thanks for any help

 

Perhaps you can share why you want to avoid the classic designs?

Or, are you seeking schematics of same?

 

too much, i just want to build a basic valve amp, that can put out 120w, dont know what the early marshall amps were like, i have seen schematics for the latest marshall amps, but they are not what i am wanting, they are all full of extra circuitry that i dont want.

 

There are hundreds of existing circuits out there, all of which are pretty similar - as for amps with 'extra bits' you just leave out the bits you don't want. Valve amps are very simple circuits, and are VERY old, tried and tested, the main concern is the price and availability of transformers - do you already have suitable transformers?, or access to some? - bear in mind the transformers are the most critical part of the project!.

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I should not have any problems with access to transformers etc, valves should not be a problem, i know people in the past who made their own amps, at the fraction of the cost of a marshall, with great success, im still not sure about the preamp, some of the new marshall amps only have a valve preamp, as thats where you notice the sound quality, i dont know how many stages i should put in my preamp, some marshall amps have 6 stage preamps, but i thought a single or 2 stage preamp would be enough.
anyway, i just want to find some schematics, that are commonly used, that i can adapt myself, i think i will go valves all the way.

 

You appear to be confused about valve performance?, it's NOT 'crystal clear', and it's NOT 'high quality', it's high distortion with a limited frequency response - quitarists like it for the 'smooth' distortion it gives.

Where it wins is in clipping, you can overdrive a valve amp, and while this causes huge amounts of distortion it's mainly even harmonics, which is less objectionable, and the limited frequency response smooths off even that.

Transistor amps clip far more harshly, with mainly even harmonics, and the far greater frequency response doesn't smooth it off at all. So it's vitally important NOT to run a transistor amp into clipping, but is common useage for a valve amp.

What EXACTLY are you trying to do?, if it's a guitar amp, and you play heavy metal, then you really could use a valve amp, particularly a Marshall type. If you're wanting it for general PA and vocals, a transistor amp is FAR, FAR more suitable, and will give much greater performance for a fraction of the cost.

Valve amps though are VERY simple devices, and VERY easy to build, after all it's 50+ year old technology - check here, just one of the many sites easily found from google! http://www.drtube.com/guitamp.htm for example circuits.

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Thats great, the information on this site is helpful.
Yes i know about the clipping etc, but i also got confused about other people telling me that valves gave you better sound quality, eg with the preamp being the most important, i will use overdrive at times, so i think i will be better off with valves

 

If you're using overdrive all the time, valves are your best option, as you're obviously using it for guitar.

Back in the 70's I used to do the PA for a local band (using a mixer I built), originally we used two LARGE 200W valve PA amps for the PA (four KT88's each), these were EXTREMELY large and heavy, and unreliable (like all valve gear) - so we replaced them with a tiny Citronic 100W+100W transistor slave amp. The Citronic not only was MUCH smaller and lighter, it was vastly more reliable, sounded a lot better, and actually seemed louder as well?.

If pushed, I'd use a valve amp for a guitar (depending on the style of guitarist), but that would be all - there's a huge amount of rubbish written about how wonderful valve gear is - but those who grew up with it, built it, repaired it, generally have a more realistic view!.

You might be aware that there are a number of so called 'valve amps' and 'valve preamps' that have a single valve fitted, which isn't actually wired to anything except a heater supply - and people pay 3 - 4 times the price of a good preamp, simply because it's got a valve in it!, even though it's not doing anything at all.

Certainly if I came across a couple of valve transformers cheap (or free!) I'd build a guitar amp, just for the fun of it - like I say, they are really VERY simple to build.

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Most valve amps will give a warmth to vocals, however the presence is lost. There's a crispness that solid state PA amps provide to give a vocal punch so as to stand out above instruments.

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My first power amplifier kit had tubes (valves). The output tubes did not stay matched for very long, one would lose its gain first and then the amp produced pretty bad distortion.
It got to the point where I wanted low distortion but I could not afford replacing the tubes every couple of months.

My second amplifier is about 40 years old, has transistors and works as well now as as it did when it was new. It has very low distortion.

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Transistor amplifiers give far superiour sound quality to valve amplifiers.

People often like the distortion that valve amps give because it recreates the classic rock sound.

There are solid state circuits that can be added to transistor designes to mimic the distortion but many purests say that they don't sound as good as the real thing.

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They don't, you're really looking for clipping the output stages, so even valve preamps don't give the 'real valve sound' - the distortion caused by clipping the output stages, as well as giving the distortion they want, also has the added effect of sounding FAR louder than the specification would suggest. You're heavily overdriving the amp, so the output will be a fair bit more than rated, but the valve distortion (even harmonics) sound much louder than clean sound.

Because of this a 30W valve guitar amp will sound louder than a 60W transistor one - however, the 30W valve amp will cost considerably MORE than a 300W transistor one!

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One BIG advantage of transistors over valves: they don't wear out !

The EL34 is also known as 6CA7. The KT77 is an equivalent.

Among valve audiophiles there is a lot emphasis put on the type of EL34.
The Russian or Chinese versions are supposedly not as good as the european made versions which command hefty premiums.


If you really must go for the authentic valve sound then maybe you should start off with a valve preamplifier using 12AX7 (ECC83 or ECC803) or 12AU7 (ECC82 or ECC802S). This would be easier to build and allow you to decide if you want to progress up to EL34 / 6CA7.

As has already been said by Nigel the transformer is the most important and expensive component and has the most significant affect on the sound.

 

And a 30W valve amp will use twice as much power as a 60W transistor amp.

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No it won't! - it will use MORE than that

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