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Old 13th Dec 2020, 1:45 pm   #1
Uncle Bulgaria
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Default Mullard 3-3 Tone Control & Preamplifier advice please

I have a friend who is keen to make a pair of 3-3s as a first foray into valve amplifiers. He asked about removing the tone controls, and also about an RIAA preamplifier.

I think the tone controls should be retained, but wondered if the best method would be to make two 3-3s with tone controls, or have a tone section in a separate preamplifier with line and RIAA inputs.

I've read the recent Tone Control threads and imagine that the circuits are more advanced than when the 3-3 was introduced. However, those threads don't have a conclusion as to the most useful circuit to use today. Morgan Jones has a detailed section on designing a valve RIAA preamplifier, and also about how it can be beneficial to reduce the gain on older hi-fi equipment to take the input from a preamplifier rather than a ceramic cartridge.

I can see the benefit of matching the preamplifier to the 3-3 to take account of driving the cables, and keeping the adjustments on the preamplifier, but I can also see the wisdom of sticking to the Mullard layout and including tone controls with each monoblock, making the preamplifier simpler.

I'm going to help him build this, so I'd like to advise him on the most suitable block diagram of the system.
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Old 13th Dec 2020, 2:15 pm   #2
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

Myself and the rest of the blokes in our class built one of these as part of our City & Guilds day release course c1965 ish, we built them to the original circuit and layout, a nice little amp with enough volume for most.

Good luck whicheverways.

Lawrence.
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Old 13th Dec 2020, 4:09 pm   #3
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

Both versions here for reference: http://www.r-type.org/articles/art-003h.htm
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Old 13th Dec 2020, 6:30 pm   #4
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

I have a set of transformers I keep meaning to use to build a stereo 3-3 with tone controls.
The circuit is interesting, to quote the mullard book

"The EF86 in the voltage-amplifying stage is used under conditions approaching those of starvation operation. With a high value of anode load resistance (R5 is l MΩ) and reduced values of anode and screen-grid voltage, the gain of the stage is raised two or three times above that obtained under normal operating conditions. This increase is attributable mainly to the fact that, because the voltage at the anode of the EF86 is very low, direct coupling can be used between this anode and the control grid of the EL84 in the output stage. Thus the shunt loading on the anode circuit of the EF86 is least at low and medium frequencies."

Peter
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Old 13th Dec 2020, 8:18 pm   #5
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

Hi UB, the Mullard amp book also has 2, nice pre amps that cpuld be used with the 3-3.
The 2 valve version should do all that is required, but the 3 vales version has a few more bells and whistles

Ed
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Old 17th Dec 2020, 6:00 am   #6
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

Some folk are sniffy about tone controls, personally after having added a SS tone control to the latest valve amp I built i can't think why, especially if the intended owner is of a certain age.

If it's the first valve amp you've both made it might be best to just build the amp itself, it's less complicated, but then he really needs to sit down and have a think what he wants. Then and again and on the other hand as a first build the acronym KISS comes to mind.

Andy.
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Old 17th Dec 2020, 8:56 am   #7
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

Have a look at the Maplin Newton. http://livinginthepast-audioweb.co.u...ium/index.html
It has tone controls and a better Phono stage than any of the Mullard designs. (Too complicated and too noisy.)
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Old 17th Dec 2020, 9:34 am   #8
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

I would not recomend Maplin Millenium 4-20 however, the original design tried to "improve" the Mullard 5-50 principly by changing component values, for example they unbalanced the phase splitter anode resistors. In a later article they basically admitted Mullard had been right all along and put the design back to mullard!

Peter
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Old 17th Dec 2020, 11:52 am   #9
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

My father built the 3-3 and 2 valve pre-amp for home back in the 60's - the tone controls were in the pre-amp.

He ran a turntable and reel to reel tape recorder (Elizabethan) through it.
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Old 17th Dec 2020, 12:42 pm   #10
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

Just a word of caution - with apologies if I'm "teaching you to suck eggs".

The Mullard 3-3 was designed at a time when loudspeakers were much more sensitive than modern ones (especially if the latter have built-in crossover networks). So you may find that the volume obtainable through today's speakers will be very disappointing - though doubling-up with stereo units will help .

I remember restoring a 5-20 for someone a while ago, and the volume obtainable through my insensitive Mordaunt Short loudspeakers was only just adequate for a domestic living room. Back in the 1960s, the then-current loudspeakers would have made an unbearable amount of noise from 20 W in an ordinary room, and would have filled a large hall adequately.

Just a thought...

Mike
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Old 17th Dec 2020, 1:22 pm   #11
Uncle Bulgaria
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

Thanks all. I've made from scratch and repaired a few valve amplifiers, which was why my friend wanted the help. My theory's hazy, but I can make sure we don't both get electrocuted. He thought the 3-3 was a simple introduction I could help him with as he's not electronically literate and hasn't done anything like this before.

He has a pre-amp, so partly out of KISS thought controls on the 3-3 would be redundant. He knows an American with heavy mystic-SET leanings so I'm proclaiming the reverse-snobbery benefits of tone controls, common components and NFB, while retaining the fun of a valve amplifier.

That's a good point, Boulevardier. This will initially be a bedroom-type system so I'm not too concerned about his existing loudspeakers. Since he's reasonably proficient at wood working it's easier for him to make some loudspeakers than it would be to build and troubleshoot a more complicated amplifier in a limited time. He's going to have to build it when he's allowed to come to visit again, so there won't be the time for a large construction to drag on.

Hence, I'd prefer to be tag-stripping a 3-3 than trying to source PCBs, or rearrange the layout for Veroboard for that Maplin amplifier. However, that's a good option for later on and I'll save those references.
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Old 17th Dec 2020, 7:23 pm   #12
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

The 3-3 is a brilliant amp. I used my home made stereo amp in the house for three years but moved it to the workshop this year.
It drove Tannoy QA 605s pefectly
I slightly modified the feedback via a control for treble boost rather than cut as my HF isn't so good these days. I find the bass control excellent with solid bass down to below 20Hz, I use top quality output transformers though.
There's a simple demo of it on my YouTube channel with pretty rubbish test speakers in the workshop. Adding an extra stage for RIAA equalisation shouldn't be a problem
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Old 17th Dec 2020, 9:19 pm   #13
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

Somewhere there is a thread on my RIAA preamplifier. I found the EF86 stage used in the valve pre-amplifier I was using was noisy and a bit short on gain and ended up with a twin triode phono stage. If you are building a stereo 3-3 it's worth upgrading the mains transformer/PSU section to power other accessories you might want to add.
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Old 18th Dec 2020, 9:27 am   #14
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

Quote:
He thought the 3-3 was a simple introduction
It is. It's a nice little amp to start with,if he builds the version without tone controls and follow the layout he can't go far wrong. If he uses a chassis a tad bit bigger than needed he can always add any tone controls etc later.

As others have said if he buys a mains tfmr that has extra current capability it gives him the chance to develop the amp further,it won't cost much more. Try and find the best OPT you can, the bigger the better. An OPT of about 10W would be grand. Hammond do an extensive range at a reasonable price as do Edcor. Not sure about Edcor but Digikey do Hammond tfmr's and as they're over 30 shipping is free and very quick, usually next day.

Lastly remember to bung a volume control on the front end, modern line sources like CD's can overload the amp that uses the original IP resistor values.

Good luck with your build, Andy.
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Old 19th Dec 2020, 3:22 pm   #15
Uncle Bulgaria
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

He's been looking at the Primary Windings offerings, as they have a 3-3 set.

It's going to be running initially through a pre-amplifier with a volume control, but I thought if it gets overloaded at line level we could put an attenuating voltage divider in, where the 3-3 volume control would otherwise be.
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Old 25th Dec 2020, 9:04 pm   #16
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Default Re: Mullard 3-3 Tone Control & Preamplifier advice please

Stick with valves for the PA stage by all means but an RIAA preamp with active filter using op amps can outperform an EF86 with very low noise and ample gain for modern pickups. There are plenty of circuits around and not too hard to build, although layout is key to minimise hum, as I found out the hard way... Cheers, Jerry
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