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Old 5th Mar 2019, 7:50 pm   #41
Al (astral highway)
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Default Re: Building a tube amp without knowlege

Hey Leon,

It's great to read the progress of your thoughts and reflections. And I can feel your enthusiasm and contagious excitement for what you want to do and can only celebrate those things, they're great!
And I'm glad that the only thing that will be glowing blue is, eventually, when you've been through safer steps, the anode of your rectifier valves...but not quite yet.

Just one thing occured to me. How are you in terms of the underlying skills like, for example, the craft/art of decent soldering?

As you will be using really quite expensive components, you'll want to make sure that when you put them all together, they work and also look really good.

Decent or better soldering will go a long way towards not only enabling your projects to work as well as they can, but also looks.

I have no idea if you have any experience in this or have acquired a level of mastery around the materials and skills, so I hope you'll take the inquiry in this spirit.

Cheers,
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Old 5th Mar 2019, 10:08 pm   #42
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Default Re: Building a tube amp without knowlege

Hi Al! Thanks for your words
It is true my enthousiam is realy big and growing.I'm always busy with vintage audio.Now i'm trying to learn repair those things i thought why not build it myself.And if i see what others can make i am sure i go also that way.
I have to admit i can solder but can't call it skills.I upgradet my €4 exploding soldering iron to a €10 soldering station from Lidl and that is an improvement.
I have lots of old things and use it for practice.Soldering things in and out is getting better and looks better all the time.I came back from using cheap things.The cheap soldering tin from China has make to take place for branded and the right tin.The cheap soldering iron works surprisingly well if i think the tips away I saw on another forum someone who replaced them with Wellers.In time i look for a decent soldering station and all the other things i need for soldering.I don't have much money to spend so i have to be creative.Like i mentioned in the previous post the most,accept a few audio things i gonna sell to finance a pair of Tannoy speakers or simulair.In the mean time i go save money and buy and sell stuff to finance the necacerry tools and the parts for a nice tube amplifier.The amplifier kits in China are so cheap i can also practice a lot with them.

Leon.
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Old 5th Mar 2019, 10:33 pm   #43
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Default Re: Building a tube amp without knowlege

I would be cautious of chinese kits, your amp will only be as good as the output transformers. My advice to you would be to buy some Hammond 125ESE or FSE, or better still the full bandwith shrouded ones if budget allows. buy a decent mains transformer and choke and LARGE chassis with plenty of room and build a single ended amp. You will be able to keep them for ever. chinese mains transformers ususlly have 220v primaries....not good for valve life.

I recently built this using an Old EMCO EMC mast controller cover as the chassis. it was intended as an introduction to my 9 year old.
fair play he cut all the holes with the qmax cutters and did a fair bit of the soldering.
only 4 watts, but thats enough to upset the neighbours.

Transformers are RS mains and outputs were made by peter chappell years ago.

EF36 6L6 or EL35 5Z4G sounds sweet.
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Old 5th Mar 2019, 11:42 pm   #44
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Default Re: Building a tube amp without knowlege

I say do it. When I was young and naive I was thrown across an airfield lighting substation by the voltages inside a constant current regulator for the runway lights. My mistake was touching a live conductor.

I'm still alive. So as long as you don't touch anything conductive and switch on at a distance, go for it.
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Old 6th Mar 2019, 12:22 am   #45
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Hi Megatron

That's a great amp and your kid must be proud he builded this without help from you
I am going to buy decent transformerswhen i decided what way i can go best with tubes and the kind of amplifier.The Chinese kits i want to try powered by a benchtransformer to get more experienced before i start with a more serious amp.Things like this will keep me busy for a while and are safe and good for learning and understanding things.

https://nl.aliexpress.com/item/1-stk...6c013f357984-4

It is not wasted money i think.I always can give it a purpose for something.I think with the parts from my broken things i can make something nice from these things.I have somwhere a kit like this with 2 little tubes what was even cheaper.On Youtube i saw many people very happy with things like transistor testing kits.For now i am looking at transformers like Hammond,Toroidy,Edcor and Lundahl. At the moment my knowledge on transformers is not good enough to decide what exact brand and type will suite me best.But i have some time untill my holday money is in.
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Old 6th Mar 2019, 12:31 am   #46
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Quote:
Originally Posted by Sinewave View Post
I say do it. When I was young and naive I was thrown across an airfield lighting substation by the voltages inside a constant current regulator for the runway lights. My mistake was touching a live conductor.

I'm still alive. So as long as you don't touch anything conductive and switch on at a distance, go for it.
I think you are right.I am thinking to paint the dangerous areas bright red and the safe ones blue.Not to think nothing can happen then but as a reminder.
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Old 6th Mar 2019, 7:48 am   #47
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You can still get cheap SE (single ended) OPT's (output transformers) off ebay for around a tenner. Get a few cheap Russian valves, EL84, ECC83 subs and a few ECC82's and find a HT tfmr off ebay (come too think of it I have a few HT tfmr's knocking about i could sell you one cheap). With a small bench power supply and cheap analogue scope your sorted or you can get sinewave's off your PC and a scope come to think of it, see "Soundcard Scope" An E12 resistor kit, some diodes and a few caps, - I built up my stash by buying 5 caps say at a time instead of the one or two I needed at the time, and that's pretty much all you need.

You can then try building a small two valve amplifier using the excellent info on Valve Wizard, keeping HT to around 250v. The first time you draw a loadline, work out what anode and cathode resistor you need, build it, power it up, put a signal in on the grid and get a bigger signal out of the anode is a revelation.

Andy.
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Old 6th Mar 2019, 4:22 pm   #48
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Default Re: Building a tube amp without knowlege

Hi Andy,i have a double bench powersupply and a scope.And also a kit for a little headphone amp.Some time ago i bought in Ukraine a bunch of NOS tubes from 1984.And i have a big pile of broken things like amplifiers an cd players so maybe i can find some useful output transformers in them.And on Aliexpress you get the caps almost for free
https://www.aliexpress.com/wholesale...f=a57oq7zzl3_1
Thanks for the tips and offer.

Leon.
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Old 6th Mar 2019, 10:29 pm   #49
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Default Re: Building a tube amp without knowlege

Quote:
Originally Posted by Diabolical Artificer View Post
You can then try building a small two valve amplifier using the excellent info on Valve Wizard, keeping HT to around 250v. The first time you draw a loadline, work out what anode and cathode resistor you need, build it, power it up, put a signal in on the grid and get a bigger signal out of the anode is a revelation.
Exactly what Andy said. It all falls into place when you see that the sums on paper translate to a predictable, working circuit. I know it sounds corny but there is something quite empowering about realising that all those graphs on the datasheets can be made to work for you.
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Old 6th Mar 2019, 10:51 pm   #50
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Default Re: Building a tube amp without knowlege

Leon,

I'm not sure how close you are to Rosmalen, but there is a radio and electronics fair coming up at the Autotron in a couple of weeks - you may well find this a good place to go hunting for parts, or even unfinished projects that will help you gain experience.

I have been in the past, a couple of times, and there is always something useful! - you may even find a professional soldering station there for not a lot of money.
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Old 7th Mar 2019, 2:28 am   #51
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I will be fair to you. I am a loser.
I have autism and don't want to use it. In a certain situations i can excel in the things i do. Forklift driving? I had not 1 but 2 pallets and it went at full speed in the trailer. Trailers?2 unknown drivers met me and thought it was gonna be a long day, I took the terminal truck, cleared the field and after that the 3 guys in 3 trucks had a hard time keeping up with me This is me some years ago https://www.youtube.com/watch?v=RVYIhRxatA0 Now i'm out of work and want to learn electronics

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Leon,

I'm not sure how close you are to Rosmalen, but there is a radio and electronics fair coming up at the Autotron in a couple of weeks - you may well find this a good place to go hunting for parts, or even unfinished projects that will help you gain experience.

I have been in the past, a couple of times, and there is always something useful! - you may even find a professional soldering station there for not a lot of money.
Sean, if you go there and need a place to stay i am your man
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Old 7th Mar 2019, 2:42 am   #52
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Thank you for all the help and thrust.This is MrSnickers and he is always against me.In the curtains while i am on the phone,on a helicopter while i'm skydiving..He is always there and my best friend.
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Old 7th Mar 2019, 4:54 am   #53
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I left the first amplifier.Someone from the local market place convinced me to drop my first plan and go this way to start.Any thoughts on my new plan
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Old 7th Mar 2019, 7:26 am   #54
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That amp looks simple for a beginner, it isn't. For a start it's class A, IE no CMRR as for a PP amp, the PSU has to be right EG very low ripple for a start, also a 300B is a directly heated valve, not easy to use for a learner, 300B's ain't cheap either. I can also see several issue's with that schematic that are wrong or badly designed. The internet is full of such schematics, all useless, it has no voltages on it for a start. If your going to chose a build at least go to DIY audio and follow one off there that has a proven provenance.

Your unlikely to find a 250v + trmr in old solid state stuff like CD players etc.

My advice, as I said, is start small, a Russian ECC83 (10 for 20 quid) and an EL84 ( or RS sell cheap valves) and an old SE OPT- build a Mullard 3-3 type amp. This amp will cost you about £30 - £50 as opposed to a stereo 300B amp = £500 and up. You can learn all the hard lesson's like high voltage safety practices,power supply design, layout, grounding, how a valve works/DC conditions/ohms law and may get an inkling of AC conditions, which is a vast complicated subject.

Make all your mistakes on a simple amp first, then you will be in a better place to build the amp of your dreams. With the amp suggested there is less chance of you killing yourself, it will be kinder to your pocket too.

Just trying to save you a few kroner and save you some hassle. Andy.
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Old 7th Mar 2019, 9:29 am   #55
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Default Re: Building a tube amp without knowlege

In electronics, it is easy to make the assumption that fewer parts = simple.

What can happen is that things with too few parts become more dependent on the exact performance of those parts, both their main parameters and also their stray effects. It is not unusual to have to select different resistor values just to get all the voltages and currents within the designed bounds.

In the amateur radio field, a lot of beginners choose what projects to build by looking at the circuit diagrams and thinking "That one looks easy, it doesn't have many parts in it" and their enthusiasm gets turned into disappointment because they can't get it working. This is very sad because they may have done nothing wrong, they just attempted a badly-designed circuit. Just having a lot of components doesn't make a design a good one.

An important part of the design business is in looking at the tolerances of all components and designing with them, so that any circuit correctly assembled from components which are within their specified tolerance should work.

I'm a professional designer. The things I design for work are built in hundreds per month. I have to do good quality designs so that any unit, so long as no faulty components are used and the assembly is done correctly should work and meet its guaranteed specifications. Having to fault-find and repair units on a production line takes the profit away and could make me very unpopular.

I've also designed a few things for my radio hobby. Some of these have been published. I've had to put equal care into their design because they get built by all sorts of people and a bad design could end up discouraging a beginner out of the hobby, and that would be a terrible loss.

We're left with the problem of needing to tell the good designs from the bad ones and the so-so ones. To look at a circuit and see design problems takes about as much knowledge and experience as it takes to design a good one yourself. This doesn't help beginners, but there are two things they can do instead... Get help from people who can judge a design, and go for something which has a track record of being successfully built.

Andy, the diabolical artificier, has been experimenting with valve audio amplifiers for some time and has been trying out different design techniques - some successfully, some not. He's found them all educational, though. He's at the level where he can do a basic amplifier with good confidence and is having fun trying things off the beaten track. His advice is sound.

The audio field is awash with people pushing their own ideas. Some are impelled by the profit to be had selling 'boutique' amplifiers at staggering prices (They fail to see that the numbers sold are so low that no-one is getting rich from it). Others hope to become famous. Some of these people are competent designers, many are not. There is a large proportion of audio consumers without any significant technical knowledge, but their money spends just like any other money and there are people trying to attract it.

So I agree with Andy's advice to start with one of the Mullard designs. They were carefully designed by a valve manufacturer to show their wares at their best. They were designed to be pretty much sure-fire when built by people learning electronics. Mullard tested them very thoroughly and since then a great many of us have built them. results have been good. They work well and are reckoned to sound good.

The internet contains plenty of audio designs touting all sorts of special features, touted with fancy prose and claims of dramatic advantages. A lot, but not all of it, is delusional. There is an aspect of the story of the emperor's new clothes. The people on this forum have backgrounds in many areas, but a lot are from the repair business where they got to see what works and what doesn't. Maths and engineering are considered a bit more reliable than hope.

David
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Old 7th Mar 2019, 3:50 pm   #56
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Quote:
Originally Posted by GlowBlue View Post
I left the first amplifier.Someone from the local market place convinced me to drop my first plan and go this way to start.Any thoughts on my new plan
The anode of the first triode is d.c. connected to the grid of the second triode: there is no blocking capacitor! So that second triode has a large +ve. voltage on its grid so it won't last very long. A major design mistake or drawing error.

Al.
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Old 7th Mar 2019, 3:55 pm   #57
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A voltage table would help, but the 160V rating of that cathode bias capacitor suggests that it's intentional.
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Old 7th Mar 2019, 5:04 pm   #58
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Default Re: Building a tube amp without knowlege

With 280V HT, 70V on the 6SN7 grid pin 1 and equal 27k anode and cathode resistors, it looks like 2.78mA Ia would give us 75V on the cathode, so Vgk would be -5V, and 205V on the anode, so Vak would be 130V. If I check the 6SN7 characteristic curves for Vak=130V and Vgk=-5V here http://www.r-type.org/pdfs/6sn7gt-1.pdf then I find Ia will be not so far from 2.78mA. Seems about right. Of course the exact operating point will be set by the characteristics of the other half of the 6SN7.

Cheers,

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Old 7th Mar 2019, 7:10 pm   #59
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With 280V HT, 70V on the 6SN7 grid pin 1 and equal 27k anode and cathode resistors . . .
Ah! That cathode R is 27k, is it? I read it as 2k7. Here, the print of that cct. is small and my eye-sight is none too good these days.
Having said that, I don't like the idea of a valve grid that is d.c. coupled to a previous anode: seems to be asking for trouble. In a simple A.F. amp. such as this, what's wrong with a conventional anode - grid RC coupling network, anyway?

Al.
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Old 7th Mar 2019, 8:34 pm   #60
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I left the first amplifier.Someone from the local market place convinced me to drop my first plan and go this way to start.Any thoughts on my new plan
It is a simple-looking circuit, with few components. And it looks 'right' and there's direct coupling to the second stage. Some of the bias and load resistors are going to bet a bit warm, it is not a very power-efficient design.

However, it won't be particularly cheap. A decent transformer to couple that 300B triode will be difficult to find. I can't help agreeing with others - go for a Mullard 3-3. Less costly valves, easier bits to get hold of!
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