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Old 13th Feb 2014, 12:27 am   #41
ronbryan
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Default Re: Mullard 3-3 information required

Do you mean Radiospares "Hygrade" output transformers, with primary taps labelled 1 to 5 and secondary taps labelled A to D?

If so, I have some connection information for that type showing taps and ratios -

Ron
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Old 13th Feb 2014, 12:31 am   #42
bikerhifinut
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Default Re: Mullard 3-3 information required

Thats the ones!

Thanks, I'd really appreciate that.

Andy.
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Old 13th Feb 2014, 12:39 am   #43
ronbryan
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Default Re: Mullard 3-3 information required

Here is the Radiospares "Hygrade" transformer connection info.

Ron
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Old 13th Feb 2014, 12:47 am   #44
bikerhifinut
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Default Re: Mullard 3-3 information required

Brilliant! Much obliged Ron.

I noticed that they are CT at 8k, I guess they could be used for a low power push pull amp. But for now its the SE 3-3.

Andy.
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Old 13th Feb 2014, 7:51 am   #45
julie_m
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Default Re: Mullard 3-3 information required

EZ81 has good enough H-K insulation to share its heater supply with the other valves.
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Old 13th Feb 2014, 12:48 pm   #46
bikerhifinut
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Default Re: Mullard 3-3 information required

Thanks AJS, I was aware of that but it's good to get confirmation. The mains transformer I am going to use came out of an old Armstrong, quite possibly the one a previous poster got the output transformers from.

The circuit did use an EZ81 sharing the heater current.
All the same, I'd be happier either using silicon rectifiers and taking an Amp or so off the transformer LT load, or finding a small 6V transformer to supply the rect.

I feel there would be issues with referencing the heaters with respect to earth if there was a bit of HT leakage onto the heaters. Why take the chance if I don't have to is my feeling on it.
I also worked out that I could probably go DC on the EL84's and EF86 heaters if the urge took me, I have a 3 amp bridge rect which would be well adequate. But that would probably be a later mod. The intention is to get the thing running properly first and then see if it needs tweaking up for lower hum and noise levels.

Thanks gents, as ever you are a mine of useful knowledge.

Andy.
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Old 20th Feb 2014, 2:32 pm   #47
bikerhifinut
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Default Re: Mullard 3-3 information required

I have gone slightly off at a tangent.
I have in the garage a single ended stereo EL84 integrated from the 1960's. Branded "Kontakt" which I think was a dutch outfit, but this thing was mass produced in japan.
Anyway, it was in need of a major rebuild and there's no circuit diagram available for this particular model, so I thought I'd cannibalise it for its transformers, I don't think it has any particular historic value or interest.
But before I take the tools to it, I noticed the mains transformer was rated at 280-280V at 85mA. This feels a bit low for the 3-3 circuit, I think I need 100mA as looking at the voltages in the Mullard book they run the EL84 pretty much at its maximum rated current. Shame if it is as its got a separate heater winding for the 6CA7 rectifier.

I've seen circuits using a 680R cathode resistor, would that take the current down? I realise there's trade offs of power loss if I reduce the current through the valve. Plus the TX is 20V lower than the one Mullard reccommend.

I thought I'd stumbled on a solution but I think I may have unearthed another set of problems.
I'm not convinced the Armstrong mains transformer would be any better, i don't know it's rating. It's got stencilled on the bottom RT102.
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Old 20th Feb 2014, 6:48 pm   #48
k_yller
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Default Re: Mullard 3-3 information required

The application of a valve depends on the designer (3-3 has specific design), but 85 mA could be enough for standard application of EL84.

Take a look at the chart.
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