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.