Mullard 3 3

[chrisnewbie]

Hi All,

After a lot of advice on another thread I think I'm going to embark on building a mullard 3 3. This is my first attempt at anything like this but I'm really keen. If anyone could give me any advice it would be rally appreciated as I'm a total beginner. Does anyone have any step by step instructions, schematics and any of the parts I'd need that I could buy.

All info greatly recieved, thanks,

Chris.

[Sideband]

You mention in your other thread that you want a valve amplifier for your stereo and spent time discussing the possible use of two matching amplifiers being used.

The Mullard 3-3 is a great little amp to build and works very well considering the circuit simplicity but it is MONO not stereo. The 3-3 part simply means 3 valve, 3 watt. For stereo you will need to build two of them. That's two output transformers required and two sets of valves, two lots of everything in fact = double the cost. Are you aware of this?

SB

[GrimJosef]

It is possible to save a few pounds by building a common power supply section which serves both amplifiers. That way you only need one mains transformer and rectifier (albeit a little larger than the ones specified for the mono 3-3) and, unless you're looking for the absolute minimum of cross-talk, one reservoir capacitor too.

Cheers,

GJ

[M0FYA Andy]

I assume you have got a copy of the book "Mullard Circuits for Audio Amplifiers"?
If not, start by gettimg one, there are downloadable copies available on the web.
Andy

[kalee20]

GrimJosef is dead right, you can save a few pounds by using a single transformer, rectifier, etc.

However, as he points out, they will need to be somewhat beefier - which means that you will need to know a fair bit to specify them. As a total beginner, I would not advise this. Better to stick to the original Mullard design, making two separate amplifiers. You will at least be able to claim a minimum crosstalk design, as per really high-end amplifiers that also use separate power supplies for each channel (probably unnecessarily I might add, although the only harm it does is to your wallet).

[GrimJosef]

Following Andy's recommendation, which I absolutely agree with, the 3-3 section of the book can be found here http://r-type.org/static/3-3.htm. The helpful introduction to building amps is also well worth reading http://www.r-type.org/static/mull-cir.htm.

There's also a section on the general principles of audio amp design http://r-type.org/static/hi-fi.htm. This is not really aimed at beginners but it does have a lot of high quality info in it. So if you have the time and inclination to work your way through it it will pay dividends. Don't hesitate to ask on here for help if you need it !

Incidentally to give some idea of costs you can get a kit of transformers for the stereo version of the 3-3 from VVT transformers. The list price for all three trannies varies from £74 plus VAT and P&P up to £165 (plus) depending on how posh you want the transformer mounts/casings to look. Or you could save a bit by buying just a couple of output transformers and hunting around for a second hand mains transformer. Of course there are other transformer suppliers too. I'm not recommending VVT in particular over any of the others. It's just that they have a convenient online price list.

Cheers,

GJ

[chrisnewbie]

Hi

Thanks for all that, would it be a good idea to get some second hand transformers as it seems that's the most expensive bit, anyone know a good supplier or is it worth putting an add on the wanted page?

I did realise that to make a stereo I'd need two so I think I'll start gathering the stuff now and begin building when I've got it all together. Thanks for the links GrimJosef, I've been plowing through them, really interesting.

Thanks again for the advice so far, I think I'll need a lot more along the way.

Cheers,

Chris.

[tri-comp]

Originally Posted by GrimJosef

I'm not recommending VVT in particular over any of the others. It's just that they have a convenient online price list.

Cheers,

GJ

And I'm saying I have first-hand experience with their products as I've just finished building an amp. using these.
X-formers for the next project already bought from them.
Fair pricees, very good electrical quality.
Mechanical quality leaves a bit to be desired.
Eventually you are able to dissolve lacquer and to remove bells for painting them and the core.
Not the easiest job in the world, but very necessary.
Also, do NOT trust dimensions given for cut-outs for drop-thru transformers.
Cut the hole only after you have the transformers on hand and can measure what's necessary.
I also bought some Hi-Fi transformers from Edcor and they are every bit as good. Finish is a LOT better but the POSTAGE getting them here...

Good luck

/tri-comp

[Sean Williams]

Will second the comment on aperture for drop through chassis transformers.......

[percival007]

I too, as a satisfied customer, can recommend VVT. Thier products are excellent and thier after sales service absolutely top notch, emails back and forth, even on a Sunday. Extremely nice people to deal with.
I believe they make Transformers specifically for the 3-3. See here:-

http://www.vvttransformers.co.uk/valve_tx_sets.htm

I made a 3-3 mostly from second hand components bought from ebay apart from the casework and am very happy with it indeed. I am no Valve expert and encountered some problems but successfully got it right in the end with lots of very friendly help from the kind folk who frequent this Forum. I would have a read through the thread, it may be of help;

https://www.vintage-radio.net/forum/...ad.php?t=55435

I would also search this Forum, entering 3-3 in the 'search box' as other people have made/repaired these Amps and there are lots of helpfull suggestions and ideas to be found.

I wish you luck and do keep us posted on your progress.

Best wishes,

James.

[G8HQP Dave]

Something which often crops up with these Mullard designs is that someone builds them in a random way and then has trouble with hum, noise or instability. Unless you know enough to design your own mechanical and electrical layout, including details of both signal and safety grounding, you need to follow the Mullard design exactly. A possible exception is minor changes in the power supply, as modern practice is rather different.

[Sideband]

Originally Posted by G8HQP Dave

Unless you know enough to design your own mechanical and electrical layout, including details of both signal and safety grounding, you need to follow the Mullard design exactly.

This is most important especially if you have not built anything before. There is nothing worse than completing the build and then being plagued with hum and noise and then spending ages trying to find out why things don't work as you expect. If you follow the layout (and Mullard knew what they were doing when they designed these amps), then at least if things don't work, you know there is a good chance that it's nothing to do with layout.

SB

[val33vo]

Mullard 3 valve 3 watt

I should think you could build such a valve amp for not a lot if you can think out of the box , second hand valves are quite cheap off the internet, the main difficulty will be the transformers OP and MAINS, but 9v secondary and 250v primary mains transformers are plentifull and cheap so you could use a pair back to back as a MAINS transformer and one as a OP transformer, I dont doubt that the purists would scorn at such an idea but it works and I doubt if you would notice much difference from custom designed items

regards

val33vo

[G8HQP Dave]

Using a mains transformer as an audio transformer was sometimes done for DIY radio equipment where sound quality was not the major issue. It would be a shame to spoil the sound of a good audio design by cutting corners like this. There is a reason(*) why decent OPTs cost money!

(*) Hints: magnetic saturation, parasitic capacitance, leakage inductance

[GrimJosef]

I'm inclined to agree with Dave. The Mullard 3-3 is a single-ended design so the 50mA DC flowing through the OPT primary generates a corresponding DC magnetic field in the core. Transformers specifically designed for single-ended operation tend to have gapped cores to deal with this. Mains transformers don't.

Cheers,

GJ

[kalee20]

G8HQP Dave and GrimJosef are right. Mains transformers will work as output transformers. And you can use two, back-to-back as a mains transformer with HT output.

However, neither are ideal solutions. For the power transformer, voltage accuracy and regulation will be less than ideal. For the output, sound quality and frequency response will suffer. It is possible, as the 3-3 has a fair bit of negative feedback, that the amplifier will be unstable.

If you know what you are doing, have these items in your junk box, and are deperate to hear sounds without waiting to get the proper items, then do it by all means! But as a permanent arrangement, it's a no-no.

[ms660]

Hello Chris the guys are right, think quality and craftmanship it's always the best practice and you will feel less inclined to rip it to bits at a later date to make something else out it (says he)

Lawrence

[val33vo]

To be honest if you want an amp that is easy to build and powerfull then just go down the transistor / IC road, I doubt if you would notice any difference apart from the cost ( I am a hypocrite here as I love valve amps myself but I think it has more to do with seeing a living glowing valve and nostalgia rather than sound quality ) To be fair valve amps do overload more favouribly than transistor ones which have severe clipping when the supply rail voltage is approached ( This is supposedly why the guitar fraternity prefer them, ie their superior quality of distortion )

As for using a mains tranny as an output transformer well its not going to satisfy a purist but I have done it and it works pretty well and a lot cheaper to boot ( nowadays )

regards

val33vo

[GrimJosef]

There are pros and cons with semiconductors and with valves. I'll concede that if you want high powers (say more than 20-30W) then a valve project will involve a bit of heavy engineering and some serious outlay on transformers. But if you make a mistake wiring up a direct-coupled discrete semiconductor amp (and I'm afraid beginners do make mistakes - I speak from experience here) then it's quite possible to blow a lot of silicon much, much more quickly than you can get to the off switch. At least with valves you can see the anodes start to glow red and power down with some chance of saving the hardware .

Just my two penn'orth of course.

Cheers,

GJ

[John M0GLN]

Originally Posted by val33vo

To be honest if you want an amp that is easy to build and powerfull then just go down the transistor

Yes, what about the John Lindsey Hood 10W amp.

http://www.tcaas.btinternet.co.uk/jlh1969.pdf

I built a couple of these after my Mullard 5-10, the design is 42 years old now, almost vintage and the 2N3055's ( couldn't afford the MJ480's ) get almost as hot as EL84's.

John