Economy Mullard 3-3 stereo amp.

[Murphyv310]

Hi Andy
Thanks for you're encouraging post. Yes they are VVT outputs, nice transformers that give a very satisfying bass.
I would also like to take you up on the speakers and will send you a PM later on in the day, have a hospital appointment this morning

[Murphyv310]

   
Hi.
The amp has now it's rightful place in the living room housed in our sideboard. I'm in the process of making up a front panel and the basic one is in the picture.
I've also replaced the mains transformer which incorporates a bridge rectifier from the single 350v secondary via a 2uf 440AC motor run cap, then fed to the EZ81 with the anodes strapped to act as a surge limiter, I did try using the EZ81 as the positive half cycle rectifier but the hum level came up and the ripple looked ghastly. Over all well satisfied.

[Diabolical Artificer]

Looks well Trevor, did you try it with those EMI elliptical's I sent you? The front panel legends would obviously look better if done with Letraset or similar but if your happy it doesn't matter. I keep meaning to have a go at silk screen printing, but I know it's not easy to do from trying it at school. The stencil is a lot of work and a bit OTT for a one off.

Happy listening, Andy.

[Crackle]

Nice sounding amp Trev.
I have recently experimented ironing on a laser printed layout to sheet metal for a power supply I am making, it can work very well, and I feel sure it could work just as well with lettering.
Print your lettering in mirror form, tape the paper with the lettering onto the metal face down.  Then wipe over the back of the paper with a cloth wetted with white spirit.
Get the wife's best iron out on full heat and press onto the back of the area where the printing is. (white spirit and heat may melt the tape so make sure you keep the heat away from the tape.)
The result can be very good, you can get al;most all the print to leave the paper and adhere to the metal and you can actually feel the thickness of the print standing proud when you run your finger over it, and it does not rub off even when scratched with finger nail.
Some experimentation may be needed but It is something I will try again instead of using letraset, or stuck on labels.

I saw the process on Blue Peter years back being demonstrated by Valerie Singleton when they made some DIY printed  T shirts.
The fainter lines around the transformer were my first attempt, but the final transformers footprint was smaller than planned.

Mike

[Murphyv310]

Thanks Andy & Mike.
Yes Andy I have tried your speakers and they are very good, the used one having the best bass response as is expected. A friend is making me cabinets but only between jobs so it could take a bit of time, in the meantime I'm using Kenwood speakers of late 80's vintage which are surprisingly very good.

Mike I like your idea, the present front panel was only temporary anyway so one better from the knee operation I'll give it a go..... Thanks for sharing your ideas.

[Terry]

It's worth mentioning that the technique described by Mike can be used for making printed circuit boards.

I might get round to trying it one day ...

[Crackle]

Hi Trevor
I am on the process of restoring a "Antoria" 1950's combination amplifier. It seems it is based on the Mullard 3 - 3 design, with an additional EF86 and tone controls.
The restoration thread is over on UKVRRR. http://www.vintage-radio.net/forum/showt...p?t=138751
The amp design works very well, I am impressed with the sound output into my 4 inch bench speaker, and even more impressed with the sound into the original 12 inch Celestion 44, even with the bare speaker driver sitting on the back of the bench, immensely  loud even at just 1 watt.
I have only just come to realise it was a Mullard 3-3 circuit, that's why I thought I would mention it on here.
Mike

[Murphyv310]

Hi Mike.
The 3-3 is an incredible amplifier, most likely the best ever single ended amplifier ever designed.
There was a basic amp that had a pre stage with proper tone controls with both bass and treble lift and cut, these were the best incarnations of the 3-3. Even tonight I got a great feeling when a local well known musician was round for a visit and heard mine..... impressed was an understatement.

[Terry]

It seems it is based on the Mullard 3 - 3 design  ...

Yes, Mike - just one quick glance at that distinctive DC coupling arrangement between the EF86 and the EL84 is all it takes!

I remember once coming across a schematic for a Grundig add-on amplifier for converting mono devices with stereo capabilities to stereo and that arrangement literally jumped of the page! The EZ80 was replaced by Grundig's customary contact cooled bridge rectifier but apart from that it was a direct copy apart from one change: the 390pF capacitor in the tone control circuit became 400pF!

[Crackle]

I'll let you into a little secret, dont tell anybody.
I reformed the electrolytics with my home made reformer but with the variac turned down a little to about 210 volts to prevent my reformer from getting up to its normal 375v. The electrolytics are only rated at 350v.
All the original testing and voltage measurements on the amp were out, guess why.


Yes, I still had the variac set to 210v, and its not the first time I have done that.    
I realised when I was checking the heater voltage to see why the amp took so long to warm up, it turned out to be only about 5.5v, then I had a   moment.

I had originally fitted a 220 ohm resistor in the HT to the first cap, but later removed that. I have now resorted to fitting a 330 ohm resistor to get the EL84 anode voltage down to spot on 290v. The EF86 anode is now spot on 20v and the grid voltage on the EL84 was about 10v.

It sounded even better on the full voltage.

Mike