Building a tube amp without knowlege

[woodchips]

What a dismal set of replies!

Of course valves and high voltages are dangerous. But then so is just about everything else, ever tipped a kettle of boiling water down yourself when your hands stop working?

As Ed says, try something with a class A at 60-80V and get the fingers in the wrong place trials over with, then progress.

A decent speaker only needs 1/2W to make some sound, use some ex-TV valves that no one wants so when you connect the HT to the heaters it doesn't matter.

I think the most dangerous things I have had to contend with in my life are the utter crap teachers at my school, they didn't know anything, so I didn't know anything. All self taught.

Danger comes in two forms, both obvious, but one is there all the time, HT rails, the other is part time, felling an 80' tree. The first requires careful working practice, the second an intense concentration as you reach for the chain saw. You can't intensely concentrate for more than a short period, 10 minutes?

[ms660]

Originally Posted by woodchips

Danger comes in two forms, both obvious, but one is there all the time, HT rails, the other is part time, felling an 80' tree. The first requires careful working practice, the second an intense concentration as you reach for the chain saw. You can't intensely concentrate for more than a short period, 10 minutes?

You can if it hangs up and it has to come down.

Lawrence.

[Scimitar]

Quite. I understand that some are scared of their own shadow, but this Elf 'n' Safe Tea business has got completely out of hand. Most aspects of life are risky but the majority of us survive it. By all means remind others about high Voltages, but don't try to wrap everyone in cotton wool. Most of the British innovation has come from taking risks and sticking two fingers up at IQ0 bureaucrats who command "Thou shalt not".

[GrimJosef]

Originally Posted by Scimitar

... this Elf 'n' Safe Tea business has got completely out of hand ... the majority of us survive it ... don't try to wrap everyone in cotton wool ...

I guess it's professionalism rearing its ugly head. Some of us had a career working with hazardous kit and we had to be grown-up about it. It's hard to let that go. If it had only been a hobby then perhaps we could have been like these youngsters who are up (literally) for a bit of fun https://www.youtube.com/watch?v=QHqAVaQqQWQ. As you say, the majority of them survive it. But if any of my staff had come a cropper because I'd encouraged him to learn by making high-voltage mistakes then I'd have been the one who had to phone his wife and tell her to get to the hospital as quickly as she could. Because, well, let's just say he's had a pretty bad shock ...

I didn't fancy ever having to make that call. So we didn't take risks and stick fingers up.

Cheers,

GJ

[ms660]

Health and safety advice comes for some good reasons, one of those is the number of dicksprings that populate the planet.....but slowly they are being educated and the attitude of some has changed for the better, unfortunately for some of the remaining ones nature will conspire and some other poor soul or souls will have to cope with the consequences of their actions.

EDIT: Was too late to post before GJ's post.

Lawrence.

[Croozer]

I don't know your level of experience, but my story might be of help. I don't work electronics or any related field, my formal education was school 'Higher Physics (ohms law, DC circuits etc) ' , but I had done some basic repairs on older technology and I wanted to design and build something of my own. At school I found valves easier to understand than transistors, and, vitally, valve manufacturers publish data sheets with graphs which allow you to undertake your own design work if you have a basic understanding of the theory. (I haven't seen the same for transistors - consequently my knowledge ends when semiconductors begin!)

The site www.valvewizard.co.uk provided that basic theory.

Over about 9 months with advice from members here and from my dad who was an electronics engineer, I designed and built an amp that, although basic, is doing sterling service with more than enough power to disturb the neighbours.

Some key points:

1. Spend some time reading about valve theory. Valvewizard is well laid out and easy to understand. There is considerable satisfaction on finally understanding those graphs!! I was on my eight or ninth working drawing before I started to build anything.

2.Get the DC circuit conditions right first. Then worry about the signals.

3 . perfectly serviceable output transformers can be got for less than 20 euros for a stereo pair second hand on auction sites. No doubt you could get better quality by paying more. They will likely be the most expensive components.

4. The metalwork is a major part of construction. It was more than I could do and something I had overlooked in an electronics project. I did the drawings for a chassis and paid a local garage to make it.

5. My first build was' pretty ' to look at - nice straight wiring, components in rows etc, but it had horrendous hum problems. Dad had one look at it and said' you want to listen to it not look at it - drawings are one thing but in the real world layout is everything'. He then gave me five layout rules which may be of use to you:

-keep anode and grid leads away from each other
-keep heater wiring away from everything else
-use a single earth point
-put smoothing components as close to the thing they protect as possible
-don't forget that transformers have fields.

My rebuild was more like a birds nest but it is hum free.

There is a link to the relevant thread below. I'll never have the skills or knowledge of the regulars on this forum, and no doubt others could build something that looks and sounds better, but the amp is mine from concept to operation and (safety considerations taken as read) I found that I learned far more than i expected and far more than if I had assembled a kit.

https://www.vintage-radio.net/forum/...d.php?t=129209

Good luck
Rob

[Radio Wrangler]

Originally Posted by Croozer

I'll never have the skills or knowledge of the regulars on this forum,

Oh, I don't know. Where do you think the regulars began?

Everyone started from zero.

When teaching someone, the biggest thrill is when they go on to do something beyond you. Without this there can be no progress.

David

[ex seismic]

You don't learn to drive by taking a Ferrari out on a race track. So don't learn valves by starting with 400VDC and 240VAC on the same chassis. As has been suggested try a valve amp running off around 60vdc so that when, inevitably, your fingers or screwdriver touches the 60v it won't vaporise you screwdriver or kill you.

[evingar]

Very well put.

[kalee20]

Originally Posted by BRASSBITS

Better to try and fail, than not try at all.

Originally Posted by ex seismic

You don't learn to drive by taking a Ferrari out on a race track. So don't learn valves by starting with 400VDC and 240VAC on the same chassis. As has been suggested try a valve amp running off around 60vdc so that when, inevitably, your fingers or screwdriver touches the 60v it won't vaporise you screwdriver or kill you.

Absolutely agree with both!

Get yourself a cheap kit, build it up, enjoy the music, have some fun, and learn lots.

Think of it as, you're not wasting money buying an inferior kit, you're paying for a lesson and some experience.

You'll make so much a better job of the 'proper' amplifier later, when you get to it!

As for safety - yes electricity does bite, so do your learning on things which are below 250V. This is high enough to teach respect, but not enough to hurt you badly. If you do get a shock, think how glad you'll be that it wasn't 400V!

[Skywave]

Originally Posted by kalee20

Think of it as you're not wasting money buying an inferior kit: you're paying for a lesson and some experience.

Ah yes: 'experience'. Experience is a bad teacher: gives you the test first, but the lesson comes afterwards. "If I had known about X, I wouldn't have done Y!"

Al.

[Argus25]

Originally Posted by Skywave

Ah yes: 'experience'. Experience is a bad teacher: gives you the test first, but the lesson comes afterwards. "If I had known about X, I wouldn't have done Y!"

I think that is right and along the lines of what Tesla said about Edison, something like; an ounce of theory would have saved him a pound of hard work.

It does seem most people want to run before they can walk, the contusions and fractures are the cost.

I think if somebody who is clearly very green in the field of electronics and or electrical engineering comes to the forum, asking for help, on a high voltage project, they should really be encouraged to start smaller than their dream valve power amplifier and work towards it more slowly.

There is so much more to learn from making smaller low voltage amplifiers first where the stakes are not as high. This is why children play with plastic swords, guns and bows and arrows, it is a rehearsal for when the stakes might be higher. Better to make mistakes when the outcome of them is less dangerous.

I'm not a believer in wrapping people up in cotton wool, but I think from what the OP has said, it would be better to start with lower voltage projects and work up. But of course this response is coming from a mature adult who has raised children. If I was a teenager with the inherent "I feel indestructible" quality, no doubt the advice would be different and I made my fair share of errors around high voltage circuitry when I was a teenager.

[retailer]

In the diy guitar amp field a 5F1 Champ is considered a beginners amp - minimal number of valves, simple SE design circuit. Many of these are built by complete newbies, people whose total electronics experience probably amounts to putting new batteries in a remote control, some are successful some not so successful. I've seen some of the not so successful ones and they seem to have one thing in common - poor mechanical skills, and poor soldering skills. The amp that blueglow wants to build looks no more complicated than two 5F1 Champs on the same chassis - if complete newbies can build a 5F1 I can't see why he can't complete the project successfully providing he has decent mechanical and soldering skills.

I did scan through some of the videos and while it is not real clear due to the lighting it looks to me that the mains connections from the IEC socket through to the fuse and mains switch are not insulated, in my book this is a big mistake and it is the first thing to do once it is verified that the mains transformer is getting power.

[pichacker]

As a kid i'd made many valve amps from scrap radio/gram parts. All worked to an extent but none survived the rip up and retry something else phases that i went through learning. Yes I got a few belts and had the occasional mishap with main smoothing caps leaving marks on the ceiling. I quickly learned what was and what was not a good idea.

I too follow Mark's youtube channel and dream of having a nice workshop in which I can bash metal into submission. A house move has put me off line for a while

Just before I moved I built a kit amp and added my own special touches. This was a VTA-ST120. It is an easy kit, with a simple but mature circuit arangement, to put together but does require some patience.

But of course that's only the beginning, from there you can modify and try out ideas as much as you wish.

The only downside is that this too is stateside and import VAT is spiteful as is shipping. I suppose it all depends upon what your ultimate goal is as to what you go for.

Don't be put off by the "Elf-n-Safety" aspect. Show the voltages respect and think about what you are doing before you go to grab something. High voltage DC hurts a lot so ensure that whatever suppy arrangement you use, you have adequate bleeder resistors so that the HT is gone when you switch off the supply.

Happy building.

[evingar]

Originally Posted by retailer

I did scan through some of the videos and while it is not real clear due to the lighting it looks to me that the mains connections from the IEC socket through to the fuse and mains switch are not insulated, in my book this is a big mistake and it is the first thing to do once it is verified that the mains transformer is getting power.

I would agree. My worst shock to date was caused by IEC socket without a boot fitted. I was working (as a rookie Test engineer) on a deep enclosure made of aluminium with an IEC socket half way up. The unit was ostensibly low voltage. Visibility was poor I assumed the senior engineer I was working with had made safe the unit before inviting me to retrieve the screwdriver that had been dropped inside.

With one hand gripping the (earthed) enclosure I used the other to "fish" for the screwdriver. While doing this the back of my wrist made contact with the Line terminal of the IEC socket . Certain words escaped that did not include "oh bother, "drat it", or "dearie me"

[kalee20]

Originally Posted by Skywave

Ah yes: 'experience'. Experience is a bad teacher: gives you the test first, but the lesson comes afterwards. "If I had known about X, I wouldn't have done Y!"

Yes. But what I said in the post was to gain the experience on something cheap that does not matter, and which nips but doesn't bite!

[Skywave]

Even time-served, trained, qualified and experienced engineers & technicians make the odd mistake, now and again.
During a past employment, I was frequently tasked with repairing 1 kW. VHF transmitters. The final stage of that had an L/C filter that fed the R.F. O/P N-type. Once, when testing one, (post-repair), whilst it was connected to the mandatory load to measure harmonic content, I was careless enough to allow one finger to touch one of those filter coils. OUCH! Yes, R.F. burns do hurt indeed! The scar remains on that finger even now.

Al.

[GlowBlue]

Thanks for all the information.Rob,the 5 points you mentioned i already readed somewhere so i think i'm on the good way.Pst days i spended only reading and watching Youtube video's.Slowly i begin to understand things better and better Also i placed an add on my local market place with a question for help.When i build the amplifier and it's time to start it up i asked for someone experienced to join me.Plenty reactions followed from people with years experience glad to help me.I'm not in a rush to make a high power amp.There are many cheap kits to practice with and understand things better.I'm not shure anymore to build the amp i mentioned.I came by this site; http://www.triodedick.com/ It is in Dutch but i think worth looking at if you don't know this man already There are some really nice projects and if i'm somewhat experienced more building little amp kits i might try one of his designs.

Leon.

[Diabolical Artificer]

Some thoughts... First off that amp will need pretty efficient speakers, if don't have any or can't run fast whilst carrying the speakers in your link, you may be better looking at another amp build or buy a PP kit.

You learn more by doing and making mistakes than watching video's or reading. I knew nothing 6 years ago but by working on various projects I've learned quite a bit in that time, although no expert, I can get by. When I first started working with valves and high voltage I was scared stiff, but have developed working practices where I'm mostly safe. Your never 100% safe, everyone here pretty much, has had a few electric shocks, it happens. If you are reasonably intelligent, careful and good with your hands you should be ok.

I can also vouch for the Valve Wizard site, there are also numerous free downloadable PDF's online to help you learn, then apply that on the workbench.

Have a go by all means, but the parts for that amp aren't cheap, using EL34's instead of KT88's would reduce the cost a bit, but you would need to make changes to bias etc. If you screw up, try again in a year or so, or you should be able to regain some of your money by selling the parts.

Andy.

[GlowBlue]

Thanks for the reply Andy and good to hear you picked it up in only a few years.The Valve Wizard site is in my favourites and go do some sudy there soon.For meto learn,it is better to do it step by step.Now i'm concentrating on transformers and chokes and the use with diffrent tubes.That's what i want to buy first for a real project.In the mean time i go play with cheap low voltage kits to practice.
You have a good point on the speakers.I am planning to sell most of my vintage gear and buy these speakers; https://www.quoka.de/hifi-audio-tv-v...tsprecher.html
In the link to the site of TriodeDick i posted before you see under for sale a pair really nice self build speakers.In the future i go look further into those.I found out that it is very expensive to start a hobby like this from scratch.Someone on a DIY-forum told me he started a project like this 8 years ago and now he has a box with parts and never finnished it.So maybe it is better to start very small and let it grow from there.I don't know.

Leon.