DIY amps (but not kits)

[pre65]

Hi-the problem i see with the old WAD and new WD kits is that they have to be sure of selling a quantity and are restricted to one configuration for each type.
what i would like to see is a written article (with pictures) describing how and why a certain amp is built with a parts list of easy to obtain components.
The Audion magazine,the Mullard book (5-10/5-20) and our own "Shadow" with his "Rocky" are examples of what i mean.
In all these cases anyone who follows the instructions will end up with a working amp with known qualities.I would love to build a "transmitter" valve amp,and there are a lot of basic circuits on the net,but they are not known quantities.It amazes me how our "senior" members hang together some of their "electrocution machines" on bits of wood.I just wish they could share the construction and circuit details with those who dont understand the theory but are capable of building with a little help.
I appreciate a lot of these are temporary prototypes and always being developed,but if we had a few basic designs for say,813-845-805-211 S/e
it might help.
What are your thoughts ?

Philip

[Bizzie]

That seems like a really good idea to me as I too can assemble kits but cannot design for myself and would love to make an amp thats a bit different.

[Gerry]

Me too!

[Paul Barker]

Best to leave the transmiting triodes until you don't need to ask how to do it.

[andrew ivimey]

Not many people do this.

there are circuits on the web, if you look. Some of these are horribly not capable of working and some are ... well you have to 'suck it and see' if you don't apply Ohms law here and there.

Not many people do that either.

the last two electirc shocks I have received were off mains, not 1kVolt etc etc and I could have got that e.g. off KEL84.

Using a hunk of mdf as a baseboard is superb, so when you get the circuit right, you can then do a proper amp on some sort of chassis.

E. G. The tractor ... I got it working fine at home. I tried lots of triode drivers; versions around 6S45 and 12GN7 and then went on to pentode 12GN7and things started cooking. But I also tried several different B+, and associated cathode resistors. I also tried several output transformers and they were all different sounding; very interesting. Overall, there was distortion and I think from the input valve. I am working now on input / driver valves; that should be v.easy. I am also up for really abusing a 6DN7 (or try 6EM7 as NickG did) but

I am NOT looking to anyone else's circuit. Who could I trust anyway? I will post as I go along but would you trust me, too?

AND - we all know that GE211 / v4tc are superb. My little stock are all 1942 vintage but so what? I got the Ongaku circuit from the web and built ... three versions. The last looks like, hm well not domesticaly acceptable but it is superb! I have never seen a real Audionote Ongaku and had to think about what goes where, drill, file, bleed all over the place and spray paint. But it is a totally wonderful amplifier.

It wasn't that James was wicked giving the tractor a challenging input with whatever that CD was, but if it can't do it then it can't. The tractor was half the current (and B+) of Nick's version with a less elegant way of sorting the 60watt heaters - but hey ! it works fine ... and it was ... half the sound. It could be compared to any 300b amplifier.

But there was distortion too and that needs sorting. NO EXCUSES.

When Nick and Paul racked things up to 1600volts well, rock on!!! marvellous.

Right now, while I am thinking about a seriously powerful driver for GM70, a very wonderful SE valve, even at a paltry 500 volts, I am playing again and perhaps 'finishing off' a modern version of WE91. It sounds excellent and I wouldn't swap it for any other amp, at home in my small room with ESS / Heil speakers. But there are still a few tweaks and this isn't theoretical. It is just experience and a little guess / try work.

If you can sort the heaters, GM70s really are the business. To hell with 2A3s and 3000bs (though I have and use both)

Paul has lent me some GK-71s. Pentode versions of GM70s? They are very busy looking, and nothing about them, circuit wise, can I find on the Web. But they are potentially enormously powerful. So I will give them a try - all 'suck it and see'.

I am learning as I go along.

If you want a superb 2A3 amp (LW) a superb 300b amp (modernWE91) or even an excellent 211 amp which is mostly done for you, phone Philip at Bluebell. I don't think there is anyone else.

If you want to 'push the envelope' well it is a bit lonely where the air gets thin but to mix metaphors, or at least add a homily, ' the first step is the hardest ... ' and then there are a few of us who will help / suggest/ advise / enthuse.

We are out there breathing thin air too!

[NickG]

Once you get past 1kv, there are very few places where you can have a chance to be clever or subtle, I could draw my 211 output stage and publish it, but it would help nobody. as Paul has said, "if you need to ask", I do hope that doesn't sound too eletist, its not meant to be. You can learn far more by building a 2a3 or 45 amp (or 6em7), and its less stressfull, The only difference between a 2a3 amp and my 211 or gm70 is its harder to find the parts for the power supply.

I am very happy with the sound my amp makes, amd was pleased that it seemed to go down well at ef3, but I think most of the quality of that sound was down to the driver stage, thats where I have spent the 100's of hours thinking, messing and listening. Again, I would be happy to tell people about that circuit, nothing special, but if I did, it would remove the chance for you to have as much fun doing your own version, and reduce the chance you would find something even better.

What was interesting talking to Jonathon at the weekend, what how I have ended up at much the same place he found some years ago, that 45 amp of his has a lot to answer for. Interestingly different from the path Andrew I, Mark and James are currently treading, I never got the change to hear Andrews amp for long, but there was certainly a lot of good things going on with Marks that makes me want to try that route as well some time.

[Paul Barker]

Of course what was not plainly obvious when Nick and I casually racked up the gm70 to 1650v is that it took me 8 years to produce that power supply, and the road was fraught with danger and littered with failures. I would not wish to publish a circuit of it, because the necessary maturity to deal with it is not developed by reading a well writen eulogy.

Chokes, transformers, rectifiers, capacitors and resistors are not just lines on a pspice drawing. They are subject to immense pressures at high voltage which can only be appreciated when you have seen them each fail to deliver. At the last you can deliver with consistent performance. Pspice would have told you the first conceioved design would have delivered.

At this level it is not about following the lines on a diagram. It is about understanding with experience. Experience is something you get the moment after you need it.

[pre65]

Hi-i hear what is being said and i fully understand all your concerns but surely any "kit" amp,even WAD or WD is going to cause the same problems ?
my point is that the more "exotic" amps are not likely to be produced as commercial items due to probably small demand.
The only one i can think of is the Bluebell 211 which Philip can do as a kit,but when i asked on the forum for opinions on this i got 0 replies.I cant afford to invest £1k on something like this without some independant opinions.
I have a copy of Audion 9 (and 7,8,10) and there is an excellent article about building a 211 amp with a PT49 (C3M) driver.I had a lot of trouble sourcing this and when it finally arived it was in Italian !!! .If anyone has facilities to translate the article (4 A4 sides) i would be happy to share the information.
I know the only way to get experience is to have a go but i dont want to build for the sake of it.
My "needs" are for a single ended amp capable of running the KLS3 so 15-20 WPC.I like the "ROCKY" design from Shadow and wondered if perhaps an EL34 PSE would be a better first project.I need to "improve" on my current Quad 11 amps but dont really want to use 300b.

Philip

[The Shadow]

Hi Phil

I don't want to be seen to be pushing my own design here but a parallel single ended EL34 along the lines of mine and Ed's amp would be an ideal first project.

I think Paul, James and Nick would be only too willing to help you there just as they did with me.

I think their concerns over HV amps like the 211 and GM70 are very well founded. One mistake and you are very dead indeed!
At EggFest 3, just being in the vicinity of that GM70 when Nick asked me to connect my preamp to his driver stage scared the c**p out of me.
And that's just the way it should be.

If you have ever been blown across the yard by a spark plug ignition coil as I was when I was 19 and working on my Suzuki GT750 electrics. Multiply that pain by about 100 and you can appreciate the dangers of KV stuff.

Even a 50V low tension supply can cause serious injury. A guy I worked with at BT lost a finger when his wedding ring shorted an equipment rack +ve bus bar to ground.

This bus bar was connected to a 200A supply. The ring instantly welded itself to the bus bar and then started to melt. The action of pulling his hand away caused him serious injury to the finger which never recovered and had to be amputated. He also received superficial burns to his face from the shower of molten gold and copper from the initial flash.

He should NOT have been wearing jewelry when working on the rack power distribution but it just shows the dangers.

I would seriously stick with 2A3s the KT beam tetrode series or EL34s. The results you can get from these devices are excellent and there is a wealth of experience of these things on this board that you could tap into.

Steve