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Old 10th Jul 2011, 6:41 pm   #81
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Default Re: Mullard 5-10 homebuild project

Pics attached.
M
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Old 10th Jul 2011, 6:43 pm   #82
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Default Re: Mullard 5-10 homebuild project

And a couple more.
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Old 10th Jul 2011, 7:31 pm   #83
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Default Re: Mullard 5-10 homebuild project

This is the section on general construction and assembly from the Mullard ref book. I can't recall whether you have this book. If not its worth a good browse thro this guy's site.
http://www.r-type.org/static/mull-cir.htm
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Old 10th Jul 2011, 10:29 pm   #84
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Default Re: Mullard 5-10 homebuild project

Quote:
Originally Posted by magnetic View Post
I think my biggest mistake was to try and combine two 5-10,s and a preamp in one box,
Well it's possible to combine two 5-10's. I did it back in the 70's but the stereo pre-amp with four EF86's remained separate. What I did was basically use two chassis bolted together (these were ready made chassis except for the holes for the valveholders and the cut-outs for the transformers). So I built two 5-10's as a mirror image of each other. The join between the two chassis formed an effective screen between the two amplifiers. At that time, both amplifiers had their own power supply so were in fact two 'monoblocks'. Both layouts followed the Mullard diagram closely and looked very much like Mike's (bonesetter). I had no problems and it was so quiet, that I left it on overnight several times by accident.


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Old 11th Jul 2011, 4:34 pm   #85
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Default Re: Mullard 5-10 homebuild project

Thanks Mike. How is your amp working out for you ? My amplifier looks like a mad octopus in comparison. I,m going to have to get my layout tidied up. I think I may just build two monoblocks,keep things simple,unless I can lay my hands on a 200mA mains transformer. Even then my layout needs attention. I,m not happy with two mains transformers sharing the same chassis/earth and the length/position of the HT wires. A few chaps have said to use a shared busbar (I think) I just dont have enough experience or knowledge really.Thank you all again for your help,its been a bit of a long haul your interest and help keeps me going,Andy.
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Old 11th Jul 2011, 8:26 pm   #86
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Default Re: Mullard 5-10 homebuild project

As I said, my 5-10's were powered by separate power supplies. Nothing except the chassis join was common between the two and each had it's own bus bar. I did think that the act of bolting the two chassis together would cause hum problems but it didn't in practice.

Theoretically, both amps having their own power supply should be better since neither power supply can affect the other. Cross-talk and separation should be better although this may be more apparent with much larger amplifiers rather than the modest 10 watts here.

The pre-amp was powered the same...left hand pre-amp from the left hand main amp and ditto the right.

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Old 12th Jul 2011, 12:34 pm   #87
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Default Re: Mullard 5-10 homebuild project

Take a look at these articles in earthing valve amps:

http://www.geofex.com/Article_Folder...nd/stargnd.htm

http://www.aikenamps.com/StarGround.html

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Old 9th Aug 2011, 4:30 pm   #88
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Default Re: Mullard 5-10 homebuild project

Hi Magnetic,

Just wondering how you're progressing with your 5-10, hope all is going well.

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Old 9th Aug 2011, 4:57 pm   #89
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Default Re: Mullard 5-10 homebuild project

Thanks for your interest Mike;at present I,m re-siting the valve holders which means I,ve had to totally rethink where everything goes. So Ive had to cut out the old top,redrill holes etc,but this time making sure heater supply and especially all wiring is short as poss. Your pics helped,I also had a close look at how other amps were laid out.

Been on the back burner for a while so I could start afresh. As soon as I get a few days i,ll crack on,cheers Andy.
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Old 29th Aug 2011, 3:26 pm   #90
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Default Re: Mullard 5-10 homebuild project

After a lot of thought Ive ripped out the old setup and started again. Tidyed it up,shortened wires etc. Its working better now but I still have issues like no noticeable increase in volume at the top end. If you look at pics the input and volume control is still in the proto type stage. Which brings me to what to do about the front end,IE wether to make a seperate preamp/volume/tone section etc.

As I understand it I wont need a preamp for CD and line type inputs. Rather I think some attenuation is in order for line level inputs. In one thread on this forum it mentioned configuring the EF86 as a triode,for such,as its too sensitive.

As for input for record deck,Ive yet to find a straight forward valve RIAA design for simpletons like myself. So may just use a simple chip job.

Lastly why do valve amps-ish and the Mullard 5-10 etc use 1-2 meg pots for tone control? Hope you all agree the layout is better,it still looks a bl**dy mess compared to Mr Tricomps,but as long as it functions I,m not to fussed,Andy.
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Old 30th Aug 2011, 9:27 am   #91
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Default Re: Mullard 5-10 homebuild project

Andy,
Your amp looks just fine. What counts is performance, not lay-out.
Just look into old Fender-amps. Often no grounding strategy (well, none obvious at least) and still they are among the most wanted and best performers.
With HiFi it's a bit more critical as you don't want ANY hum/hiss and preferably no colouring by valves.
Actually I think the amp. is perfect when YOU are satisfied with the output produced. Of course you may have to revice the construction to get there but that's called experience and that can't be bought

Thanks for taking an interest in my project.

rgds,

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Old 30th Aug 2011, 2:49 pm   #92
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Default Re: Mullard 5-10 homebuild project

Yes, don't copy guitar amp practices when building hi-fi. They coped with poor layout by ignoring noise and hum, and adding big grid stoppers to stop instability - so the HF limit could be as low as 5kHz and critically dependent on the valve parasitic capacitance multiplied by Miller effect.
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Old 30th Aug 2011, 5:50 pm   #93
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Default Re: Mullard 5-10 homebuild project

Valve amps use high value pots for tone control because the valves themselves are high impedance devices. Consequently low values of pot resistance would cause too much loss of signal to be useful.

In any case, with a passive tone control if you want 20dB boost at the extremities of the frequency range, you have to have a 20dB loss in the flat position which is bad enough to start with....

It's unfortunate that suitable high value pots are less easily obtained nowadays than when everybody used them!
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Old 30th Aug 2011, 6:55 pm   #94
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Default Re: Mullard 5-10 homebuild project

The amp is working alot better,I,ve lost the bad distortion,But am at a loss as to why it doesnt seem to be kicking out its 10 - 14watts. All DC measurements are pretty much smack on. But in the Sterns layout/design it uses 270 ohm cathode resistors for an OPT primary R of 8K. The VVT OPT,s I,m using are 6k;the mullard bumf says I should use a cathode R of 437 ohm. Could this be the cause of loss of power?

Would anyone advise me please on wether I need to reduce the input of say a line level input like a CD,before it enters the EF86? And comment wether I should configure the EF as a triode for such inputs as CD,computor,etc. Things have moved on in the 50 years or so that the 5-10 was designed. I,m at a loss as to how to connect such modern devices such as CD,PC etc. I,m getting a distorted signal when feeding a CD output straight to the amp. Is there an industry code such as RIAA that dictates the values of such?
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Old 30th Aug 2011, 10:01 pm   #95
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Default Re: Mullard 5-10 homebuild project

If you use 'low loading' (6k impedance, 437ohm cathode resistance) you will get the same output on music (and lower distortion), but you can't do sine wave testing to measure the maximum output power. This is because the signal causes a bias shift.

I would not feed a CD directly to an EF86. OK via a volume control, or a fixed attenuator, but then you are reducing the signal only to amplify it again.

Even if there was an industry standard for voltage levels, there is no guarantee that people would stick to it for domestic equipment. Generally, levels are higher now especially from digital items. Exception is pickup cartridges, where MM is about the same and MC (not used much back then?) is smaller.
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