Stereo valve amplifier

[Diabolical Artificer]

Having looked at this a little myself I,m going for a couple of Mullard 5-10,s.I would have started with the Mullard 3-3 design but managed to aquire a couple of old home built 5-10,s.There are very comprehensive,very detailed plans online for the old Mullard designs.
Your most expensive components apart from the valves are the transformers,but look on Ebay at Parmeko etc mains and output transformers.The ones I looked at are cheaper than new ones in some cases.
Secondly,as to making the chassis,if it was me,I,d look up local engerneering firms,you can get the top plate laser cut for very little(in comparison)What they do with a laser is incredible.Most firms need the work,a friendly chat in the right ear...?? Four side pieces of wood,a little bit of routing and bobs your uncle.
When I looked at kits,I was overwhelmed by the prices they are asking ,£1000 in most cases,also I found it hard to decifer the spiel surrounding valve amps.
Lastly there are a few online DIY projects such as the AX84 tube amp project,which is well worth a look at.
Best of luck,Andy.

[qualityten]

Originally Posted by bluepilot

Kits may seem expensive but I suspect only because you are buying all the components at the same time. If you buy everything separately then the individual items may seem cheap, but by the time you add them all up plus the postage then it can well end up expensive. I discovered Ebay article 170591573314 which seemed to be reasonably priced to me considering it includes everything. Of course you may prefer to bend and drill the chassis yourself, but winter won't last for ever

This looks good, though I'd prefer one with 2xEL84 per channel. (I have a Heathkit amp with 1xECL86 per channel and it could do with more oomph.) I see item 180551081085 is for 15W per channel modules, but that is back to more of a self-build.

[Aerodyne]

I think it is worth asking yourself why you want a valve amp. If it is simply as a sound reproducer, then a ready-made or kit amp will certainly deliver the goods. If, on the other hand, you see it as a project, something to be done for the pleasure and satisfaction to be gained from the creative process, I'd recommend making the chassis yourself.
And anything else that can be made satisfactorily by hand - socket strips, transformer enclosures, control panels and so on. The electronic design can with advantage be partly or almost entirely of your own making - though as I've indicated earlier, my preference is to start with a known and respected design and modify lightly to suit your needs.
Watch out for those 'cheap' transformers, though. I know that occasionally some will appear but if and when they do, look for the name and try to ensure they are made for high fidelity valve amps and not simply for guitar amplifiers. A known name such as Parmeko, Gardners or Elstone should be safe.
-Tony

[learner pianist]

Dear all,
Many thanks for all replies to my request on building a stereo amp. It would seem that the Mullard 3-3 has a lot of support so I shall probably go for this. However, there are some other questions that I now have:-
1. I need to buy some speakers(bookshelf type)-there are many to choose from but I note that the spec for all of them gives amp power in excess of the output of the Mullard amp-examples being 25-30watts, 20-100, etc. I have not seen any that will handle only 3-watts. Am I missing something or should I be considering a higher output amp-I am quite sure I would be happy with the Mullard 3-3. Any advice?
2. My turntable has a magnetic cartridge with an output of 4-6mV. I assume this is not enough; what is the simplest way of increasing this?
3. Finally, I assume from the description of the Mullard 3-3 that to acheive a stereo amp, you should build two amps-do you use double gang controls ?
Is the power circuit common to both sides of the amp? Would the transformer quoted for use drive both sides of the circuit?
4. Sorry-just one more thing-the reproduction of the circuit off of the web is not very good-can anyone direct to where I might get a more readable circuit diagram.?
I expect all of this is fairly basic stuff to all of you out there-please forgive the simple questions.
All replies gratefully received.
Barry

[Aub]

Hi Barry,

I use a little amp i made that uses an ECL86 in each channel, so output power is not too different from the 3-3. My speakers are a pair of KEF bookshelf units ( Coda 10, if i remember correctly ) and volume is more than enough, from most recordings, to fill our lounge. Most hi-fi speaker's power handling will be way above the power output of the 3-3, ( I think my KEFs are rated at about 75 watts RMS ) but don't worry.

Good luck!

Aub

[percival007]

Hi Barry, as Aub has said, do not worry too much about the Watts. It would be the 'Sensitivity' of the Speakers that would be of most concern. This is measured in dB's.

For example i use REGA ELA MK1's with my 3-3 which are quoted as being 89dB in respect to thier sensitivity. This actually means that for an input to the Speaker of 1Watt, measured from 1 metre away, the Speaker produces 89dB Sound (Pressure? Please someone correct me if i'm wrong here). So, the more dB's the speaker is quoted as having in the Sensitivity specifications the 'louder' your 3-3 will sound.

My advice would be to make your 3-3, then take it with you to a Hi-Fi shop. A good shop should be happy to let you test several speakers with your Amp to find the right pair for you.

Yes, you can use dual ganged controls. I have for the input and the Volume. I have made the version without tone controls.

The power supply as written will supply two channels, you could though use an EZ81 rectifier if you want to give a little more headroom. Also choose your Mains Transformer to match.

This circuit i found to be most usefull :-
http://www.r-type.org/static/3-3.htm

All the very best,

James.

[Aerodyne]

The 3-3 requires 100mV for 3 watts output per channel. You will need some sort of preamplification to boost the signal from your pick-up. This could be transistor or microchip based.
If you intend to build on a single chassis it makes sense to use a single power supply. The stereo 3-3 I built in the late 1950s used a 5V4G rectifier - power in plenty there, but the EZ81 as suggested by James will also serve. Your problem will be the locating of gang stereo pots of the correct value. If you get stuck, take a look on the links/suppliers section on my website www.vintageradioworld.co.uk
-Tony