Building a tube amp without knowlege

[Croozer]

I understand all the hype about 'triode quality' might seem attractive but a Pentode will give much more power more easily. In my view the EL84 (and ul84, pl84) marked a high point in valve design. High output in a small bottle at low cost.

For a first time build I suggest you want valves that will be tolerant of operating under a wide range of conditions. The EL84 could be driven directly from a crystal phone cartridge in basic old record players and with relative low HT so is a good choice.

Most output Pentodes typically need a voltage swing on the grid of around 10-15V to use them to their best. The line output of, say a CD player will typically be 0.5V, so a second valve is needed as a voltage amplifier to 'drive' the Pentode. The ECC83 is a workhorse high gain valve designed for audio work. Again it will operate under a range of conditions including low anode volts. The fact that it has a high gain means there will be enough amplification to use negative feedback to improve quality (this is feeding back the 'reverse' of the output to the input, consequently holding down the overall gain). An ECC82 could also be used here but the gain is lower, limiting use of feedback.

The two valves are connected together with a capacitor which allows the AC signal to pass from the first valve to the second, but prevents the high voltage of the first anode reaching the grid of the second valve.

I've drawn a basic circuit to give a start and to illustrate the main points. There are 7 capacitors and 8 resistors so plenty of design options, depending on factors such as HT.

This is intended as an example topography using the valves discussed further up the thread. I'm no expert and there are no doubt better ways of doing things than this and others here will be able to suggest additions and subtractions to make improvements.

Main points :
C1 and c2 protect your input device from direct DC connection to the amp.

C5 is the coupling capacitor described above.

R7 makes the cathode of EL84 more positive than the grid, setting the bias which allows the valve to function. C4 bypasses this for audio frequencies, preventing the valve creating its own negative feedback circuit.

C6 is a tone correction capacitor, bypassing high frequency, preventing overemphasis of treble.

R8 controls the amount of negative feedback. You can alter the tone by changing C7.

HT1, HT2 and HT3 are the three High voltage supplies which should all be decoupled from each other. HT1 is the highest, typically designed at 250V but will work on significantly less. HT3 need only be 100V

[Sideband]

Originally Posted by GlowBlue

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 title of this thread is 'Building a tube amp without knowledge'. You have come here for advice and help and I would strongly suggest you take the advice given....most of us on here would say the same or very similar. You will have MUCH MORE SUCCESS building tried and trusted designs like the Mullard 3-3 which were designed by professionals....in fact the same people who made the valves (tubes) rather than the 'boutique' designs using hard-to-find (= expensive) valves with apparent 'mystical' sonic qualities and questionable circuits.

Stick to the tried and trusted circuits that we all know....you asked us....we're advising you.... Obviously to get the very best results from the 3-3, you do need a good output transformer but to start with, it's not essential and a modest transformer will give good results...there is always room for experimentation later.

A few years ago, just for fun, I built a 3-3 on a scrap chassis using junk-box parts and didn't even take much care over the layout just to see what you could get away with. It worked surprisingly well using just a small output transformer from a scrap radio....limited output admittedly but very good quality into a small bass-reflex speaker enclosure.

Ultimately it's up to you of course but I think if you start with an unproven design it will end in tears and probably wasted money......

[Uncle Bulgaria]

I just felt like doing a bit of general back-slapping - what a resource where someone with no knowledge can pop up and get four pages of cogent response, including bespoke circuit sketches, purely for the purposes of advice.

There's a reason I'm hanging out here these days rather than DIYAudio.com.

['LIVEWIRE?']

If it's not OT to mention it here, I find members of DIYAudio.com very helpful, as indeed are members of this forum, and GVR.

[Junk Box Nick]

As an amateur enthusiast I endorse what Sideband has said.

In my youth I built many miracle designs that were published in various magazines - especially when few components meant minimal spend from meagre resources. I had more failures than successes and I paid a high price in frustration.

Had I had a bit more knowledge I would have spotted the compromises and indeed mistakes in the circuits. Sometimes the former and not infrequently the latter could be found in very 'respected' books. I still have some of the abandoned specialist components from those days and I wince at my waste of hard to come by money.

'Tried and tested' may not be a fashionable concept but when you're a novice it's the best approach.

You'll get excellent advice and help on here. In this field of activity many of these guys have forgotten more than I've ever known.

[GlowBlue]

Thanks for the advice you all give me.I want to make a point.In earlier days you had a magazine and a experienced man to learn you the basics.Now in internet times there is much more information.The man with knowledge is gone and there are now 1000's of them on a computer screen all conflicting with eachother.Past days i got lost in information and conflcting approaches.With all respect,from now i go only 1 way.Otherway i ever learn why and how.
*i go for a triode single ended amp
*this man's design i go follow and try to build something off his designs http://www.triodedick.com/
*The start will be a package of this man's Transformers; https://www.mennovanderveen.nl/cms/i...3035-se-detail

It does not make sense leave every option open.This is the way i go.Both TriodeDick and Menno van der Veen are in the Netherlands and guys like us.They love Tubes

So with that in mind,suggestions are welcome

Leon

[GlowBlue]

Here are my children. The small cat had a hard time in it's past and the dog i take care of to prevent his owner had to make a choice quit work or leave the old man (12) I want to say i go not cheap in doing things.It happens i am away for a few days.If i met a girl or i get lost in things.I respect the feedback from you I am unlike gathering information and then stay away.Hope you see all information is like a Tree.Sometimes things grow beyond your hat ****************/HPFzh0t


Leon

[julie_m]

If you really want to build a valve amplifier, as opposed to building a kit by slavishly following the instructions, you will have to learn about valves. And the best way to learn about valves is to do experiments with valves, and talk to people who know about valves (this forum takes care of that part nicely). Part of the beauty of valves is, you really could almost see them working if only electrons were not so tiny!

I had great fun -- and learned things, too -- building a little ECL80 amplifier and solid-state vibrator HT power supply to run from a 6V rechargeable battery a few years ago, using mostly parts-drawer components, and going through a few design iterations before being deemed ultimately successful.

I used an "experimenter board" with A-D and D-A converters plugged into my laptop computer to generate some Ik\Vg plots for each electrode structure, and set the bias to give me an operating point smack bang in the middle of the straightest part of the graph.

The main part I didn't already have was the speaker transformer, which came from RS Components. The PSU used a c.40x15mm. ferrite toroid core, hand-wound with 200 turns on the secondary and 7+7 turns (bifilar wound, i.e. a doubled-up strand laid side-by-side) on the primary; driven by a pair of power MOSFETs from the Q and Q! outputs of a 4047 running at about 40kHz. (The original plan had been to use a salvaged mains transformer "in reverse" at 50Hz., but this proved unworkable due to transformer losses. The nearest thing to hand was this chunky toroid .....) The HT was about 140V DC.

The battery supplied the heaters and also a separate grid bias voltage to each section, so as to get around any issues with the common cathode. (It was found in the end that the two bias voltages were quite close anyway; but it did not hurt to be cautious, and it also saved some volts of HT.)


For your first valve experiment, try dimming an LED in the anode of a triode (if you join the second grid of any pentode to the anode, then it will behave as a triode) by applying a negative voltage, adjustable by means of a potentiometer, to the (first, if you're using a "strapped" pentode) grid.

N.B. If using any kind of rechargeable battery for an experimental heater supply, make the final connection to the battery using only one strand of stranded hookup wire. In the event of a short-circuit, this will act as a (primitive but effective) fuse and prevent a fire or explosion. Even small rechargeable batteries contain a lot of energy and can deliver it all very quickly -- as you can nowadays see at no personal risk besides maybe feeling a bit sick, thanks to YouTube! I got through a few of these poor-person's fuses in the course of my experiments; I might not have been here to tell the tale otherwise. (Of course you should fit a suitably-rated glass fuse in a proper holder, when you build something more permanent.)

Good luck and enjoy the ride And don't be afraid to ask questions!

[Uncle Bulgaria]

Originally Posted by 'LIVEWIRE?'

If it's not OT to mention it here, I find members of DIYAudio.com very helpful, as indeed are members of this forum, and GVR.

You're right - my comment came out rather more negatively than I intended! I meant that this forum is small and coherent enough by comparison that it feels more individual. On others there's a higher proportion of argumentative posts.

Back on topic: my first amplifier was a single-ended 6SN7/300B power and 5687/ECC82/ECC83 phono/line pre-amp I made ten years ago under the supervision of my grandfather. My only experience previously was repairing household electricals and A-level Physics. I've had a shock or two and wouldn't recommend starting with something like this without an attendant grandfather!

I have since tried designing my own amplifiers, and repaired radios and hi-fi and second a previous poster's recommendation of Valve Wizard, and also Lenard Audio's series. They've been extremely helpful. I also purchased a series of books designed for the new radioman/electrical engineer during the last war - 'Basic Electronics' by the wonderfully named Van Valkenburgh, Nooger & Neville. Simple explanations with clear drawings, and all about valves. I can even interpret some simple circuits now, and do some of my own diagnostics.

[AC/HL]

We're not in the business of scrapping equipment here, even ones considered beyond earthly help by most people. However, the world is awash with old radios and tape recorders which will never be wanted, and which will gradually be recycled (or worse).
Any one will yield all the expensive parts required to build a simple 3 watt amplifier for learning and possible future use. It already exists of course, but you'll learn much less that way.

[julie_m]

A tape recorder is almost certain to have a transformer-isolated power supply. If you can find one that is mechanically beyond repair, it will most probably yield up an ECC83, an ECL82 or 86, and suitable mains and loudspeaker transformers. The transformers are the limiting factor, but you will at least have all the bits you need to start experimenting with.

[AC/HL]

Yes, I should have stressed that, any radio must have a mains transformer, not one of the universal AC/DC ones.