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Old 25th Jan 2022, 10:19 pm   #1
Gabe001
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Default Mullard 5-10 build

So my rather ambitious 3rd amp build is going to be the iconic Mullard 5-10. It would be interesting to see how it sounds next to the ultralinear Olson based build, and how the el84s sound c/w the 6v6s. I'll follow the instructions in the Mullard book for the component layout etc

It's going to be a rather major undertaking as you can see from the sorry looking chassis (it was free), so I've decided to write it up here as an ongoing project. The resistance readings on the mains transformer seem to check out.

The OPT looks larger (thicker - not appreciated in the photo) than other p-p 8k 14w I've seen (not that many!) and someone went to great lengths to create a metal bracket to mount it horizontally rather than vertically. It's the standard (non ultralinear) p-p versionwith no identifying marks. The worrying issue is that half of the primary measures 255ohms and the other 295ohms.

The case will get sanded down this weekend and will get sprayed with hammered black hammerite for a nice industrial look.

The mains and OPT look much better after a coat of gloss enamel and a clean.

I'm considering whether to try the current OPT first,or to get the ultralinear primarywindings one. Probably the 5-10 is worth spending a bit of money on so I'm leaning towards the latter.

I have all the valves and some spare valve holders, fuse holders, tag strips etc. The chassis is the one with the controls, but I'm not sure if anything other than a volume control is worth adding as I can use the software equaliser on my phone or laptop. realistically I will only be using it with digital files; my vinyl player is a Pye black box.

I know that I've got my work cut out.

Any thoughts, other than that I've probably taken on a suicide mission?

Gabriel
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Old 25th Jan 2022, 10:40 pm   #2
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Default Re: Mullard 5-10 build

Hi Gabriel, that should come up nicely.
The OPT looks a good size, so should sound good.
Note that Hi Fi OPTs often have the sec in between the 2 pri halves. this means the outer pri has a bigger mean length of turn and hence higher resistance.
You could try feeding say 2v 50Hz to the sec and see how balanced the voltages are on the 2 halves of the pri

Ed
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Old 25th Jan 2022, 10:55 pm   #3
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Default Re: Mullard 5-10 build

Its not a suicide mission . It should work if you follow the origional article. It will teach you more as you go and thats the important thing.

er just a suggestion, why not paint the chassis with aluminium coloured paint? It does look rather sad.

Joe
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Old 25th Jan 2022, 11:51 pm   #4
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Default Re: Mullard 5-10 build

I have to say, having built both when I was a teenager, I preferred the sound of the 3-3 to its bigger brother. Trouble was I used bits of the 3-3 to build the 5-10 so there was no going back. Maybe a 3-3 should be your fourth build Due to the large amount of feedback the 5-10 is very layout sensitive so follow the instructions carefully and check for oscillations. The tone control-less version is also very sensitive by modern standards (40mV) so volume control definitely required.
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Old 26th Jan 2022, 7:40 am   #5
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Default Re: Mullard 5-10 build

The 5-10 was the first amp I built and was far too sensitive for modern sources, it distorted line OP's like PC, CD etc. Knowing what I know now I wouldn't build it, I don't like the ECC83 phase splitter or EF86 front end; way too much gain. The 5:10 was built to showcase Mullards new range of valves and though well designed it's a product of it's time, most of the traditionalists here won't agree with me. There's been various tweaks done to the standard circuit over the years to address some of the points I've made that might be worth looking at/thinking about.

Re a PW OPT, last OPT's I bought from there took a long time to arrive, he was and still might be very busy.

Andy.
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Old 26th Jan 2022, 1:14 pm   #6
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Default Re: Mullard 5-10 build

Thank you for your comments

Ed: yes Jerry said the same thing about the winding. We were a bit worried that 40 ohms difference sounds like a bit too much, but I'll try it and see

WD: there are lots of 3-3 fans around here. I keep hearing good things about it. I'll consider it. It may sound a bit tame with my speakers though.

Andy: I've been looking at running the ef86 in triode mode which seems to be quite a well established mod to decrease input sensitivity. I'll need it at around 300-400mv RMS. Re ecc83 as a LTP splitter, I honestly don't know, which is partly why I want to build it. My other 2 builds were cathodyne amps and they both work well (12au7 and 6sn7). I can do cathodyne in my sleep but I've never heard anything different to a concertina so far

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Old 26th Jan 2022, 3:01 pm   #7
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Default Re: Mullard 5-10 build

The 3-3 is a great little amp. I built several over the years including one to replace an amplifier in a record player. It sounded so good I had to fit a larger speaker and then built a second (external) one for stereo. They ended up driving a pair of small Celestion speakers....many a good party was had with those little amps!
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Old 26th Jan 2022, 3:05 pm   #8
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Default Re: Mullard 5-10 build

On page 53 of this book the values for the EF86 connected as a triode are given:

http://www.introni.it/pdf/Rodenhuis%...20Circuits.pdf

The schematic in "circuit description II", starting on page 46, is almost identical to the Mullard schematic. The only small differences I see are in some of the values of the feedback resistor and capacitor (R11 and C6 in the Mullard schematic; R6 and C5 in the Philips schematic).
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Old 26th Jan 2022, 5:27 pm   #9
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Default Re: Mullard 5-10 build

If you want to reduce gain just remove the EF86 cathode bypass capacitor if that goes too far insert a resistor in series with it instead.
 
Old 26th Jan 2022, 5:54 pm   #10
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Default Re: Mullard 5-10 build

Hello,

If its of use I’ve uploaded the diagram for the STD381 Amplifier, which is basically, a commercial stereo 5-10 with triode connected EF86 with feedback components to the give a lower input sensitivity.

There is an error in the power supply as R18 and 19 should be 100Ω

This could also help with a starting point for any triode tweaking.

Hopefully the pictures are OK. The ZIP file contains all the .JPG's

Terry
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Old 26th Jan 2022, 9:59 pm   #11
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Default Re: Mullard 5-10 build

Thank you Robert for the pdf, you always have really great literature. You helped me a lot with the 6v6 UL article too, which was a really good one I hadn't come across.

Thank Terry too for the schematics. I will study them in detail and compare them to the original. looks like minor component value changes, no drastic changes.(which is good)

Joe, your post appeared late for some reason. I'm painting it hammered black. The "suicide mission" mostly refers to the sorry cosmetic state of things currently. Everything will get sorted.

So, one question, how much is it meant to hum/hiss? I mean ear to the speaker noise - I know it'll be silent standing a couple of feet away from the speakers.
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Old 26th Jan 2022, 10:45 pm   #12
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Default Re: Mullard 5-10 build

It looks like this was a PP amp before? Have you checked the output transformer ratio and the mains transformer voltages?
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Old 28th Jan 2022, 10:04 pm   #13
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Default Re: Mullard 5-10 build

Thanks for the interesting comments in this thread on the classic 5-10. Building one of these following the guidance in the Mullard book gives one an understanding of most of the 5-10 clones that appeared in the late 50s and early 60s. http://www.r-type.org/articles/art-003e.htm. To my ears they all sound good, but that's because it's hard to make a bad sounding amplifier using EL84s.
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Old 29th Jan 2022, 12:24 am   #14
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Default Re: Mullard 5-10 build

I'll be following this thread - I'm also wanting to build a similar PP EL84 amp in stereo, I hadn't yet decided on a circuit but had a few in mind - Leak Sereo20, Mullard 5-10 or one of our locally grown examples the RTV&H Twin 10. I've attached a zip file of the RTV&H Twin 10 magazine build article - doesn't look a huge amount different from the Mullard or the Leak but does make a good read.
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Old 29th Jan 2022, 12:47 am   #15
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Default Re: Mullard 5-10 build

The Leak Stereo 20 is also a very sensitive amp - 125mV in for full output. It's a lovely thing, but works more reliably in the later version, with the 25% screen tappings on the ouput transformer primary (or use Russian EL84 equivalents - the 6P14P-EV or 6P14P-ER versions should survive better in the original design, with 49% screen tappings).

Cheers,

GJ
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Old 29th Jan 2022, 8:42 am   #16
Gabe001
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Default Re: Mullard 5-10 build

Which is you favourite stereo amp GJ? I am considering one as a project after this one
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Old 30th Jan 2022, 6:00 pm   #17
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Default Re: Mullard 5-10 build

Been removing rust, sanding and spraying today. Top side sprayed black; once it dries I'll do the underside.

The transformers have been cleaned, rust removed and painted with gloss black enamel. Its already looking much better

I'll post some pictures next weekend once I've reassembled.
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Old 30th Jan 2022, 11:18 pm   #18
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Default Re: Mullard 5-10 build

Black inside the chassis too?? hhmm maybe not so clever an idea. After 50 years of building amps I spray the insides with light grey flat paint. It allows resistor colours and wire colours to be easily seen.
The guitar amp has been sitting upside down for about 2 years Hence the dust buildup.
Joe
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Old 31st Jan 2022, 3:07 pm   #19
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Default Re: Mullard 5-10 build

Hi,

Merlinmaxwell is quite right suggesting this method, as in some cases triode connecting the pentode (EF86) first amplifier valve will also reduce the open loop gain too far and the original feedback level can’t be obtained with the (new) desired input sensitivity with a triode first amplifier.

Terry

Quote:
Originally Posted by merlinmaxwell View Post
If you want to reduce gain just remove the EF86 cathode bypass capacitor if that goes too far insert a resistor in series with it instead.
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Old 31st Jan 2022, 7:57 pm   #20
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Default Re: Mullard 5-10 build

I've just altered my homebrew control-less 5-10 to triode-connected EF86 using the component value changes identified in Robert's Post #8. It is driven by one half of a Quad22 control unit, the other half driving a Quad II. The only difference my ears can detect is that the 1M volume control setting at the 5-10 input has needed to be increased, to compensate for the reduced gain, as expected. Still sounds just as good as it did before. I think if you want to be a purist the only way to compare objectively is by measuring frequency response. I shan't bother - life's too short! Cheers, Jerry
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