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Mullard 5-10 amplifier.

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Till Eulenspiegel
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Found this Mullard 5-10 amplifier upstairs in the stock room, or to give it's correct name the junk room.

5 10amplifier 1
5 10amplifier 2

 Back in 2015 I serviced two Dulci DPA15 amplifiers which were based on the 5-10 circuit design:

https://www.radios-tv.co.uk/community/amps-turntables-radiograms-ampreceivers-etc/two-dulci-dpa15-amplifiers/

Bought from RS Components for use in the amplifier made in China EL84 valves.

5 10 RS EL84

  Let's find out if the amplifier is any good.

Till Eulenspiegel.

 
Posted : 08/02/2020 10:00 pm
ntscuser, Nuvistor, PYE625 and 6 people reacted
PYE625
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Very nice !

You do realise that without Mullard EL84 having square getter's and original white print on the envelopes you will not get the full sonic benefits of a walk-through soundstage with the true realism of that classic full bodied tone? You will miss the audio detail that hangs beautifully in the air beyond the loudspeaker that enriches the very soul of music. The true authentic ambiance of the real live recording may be slightly foggy and somewhat obscured. It may sound slightly veiled and intrinsically missing that certain something.

Or, I could be mocking the truly gifted who can tell the audiable difference a silver plated mains fuse can make. ? 

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 08/02/2020 11:12 pm
ntscuser, helloekco, Nuvistor and 9 people reacted
Till Eulenspiegel
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 ….but who knows those made in China EL84s might be rather good.  Note the blackened anodes, that's got to be a good thing. From r-type.org.  Lots of info about the Mullard 5-10 amplifier:

http://www.r-type.org/articles/art-003e.htm

 

 

 
Posted : 09/02/2020 12:57 am
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PYE625
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Seriously though, I do like a bit of Hifi restoration and am really looking forward to reading more Till. ? 

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 09/02/2020 9:30 am
sideband
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Posted by: @pye625

Very nice !

You do realise that without Mullard EL84 having square getter's and original white print on the envelopes you will not get the full sonic benefits of a walk-through soundstage with the true realism of that classic full bodied tone? You will miss the audio detail that hangs beautifully in the air beyond the loudspeaker that enriches the very soul of music. The true authentic ambiance of the real live recording may be slightly foggy and somewhat obscured. It may sound slightly veiled and intrinsically missing that certain something.

Or, I could be mocking the truly gifted who can tell the audiable difference a silver plated mains fuse can make. ? 

....Did you by any chance ever watch 'Yes Minister' or 'Yes Prime Minister'? This is just the sort of mumbo-jumbo modified by poilitcal statements that that classic comedy used to feature..... ? 

 
Posted : 09/02/2020 10:21 am
PYE625
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No, but I worked in the Hifi industry for many a year and used to read such waffle in the magazine reviews of equipment from time to time.

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 09/02/2020 10:58 am
Cathovisor
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I remember when hi-fi reviews switched from objectivism to subjectivism. Some subjectivism is needed, as bland frequency sweeps and noise measurements aren't ever going to give you a full picture of what an amplifier actually 'sounds' like with 'real world' material, but it has got rather into the world of wine-tasting these days.

And nowhere is this more so than in the world of valve-based equipment: as I have long maintained, nobody in the world of transistor amplification ever said "this amp sounds better with NXP transistors fitted", for example. But I'll bet there's a fringe that does!

 
Posted : 09/02/2020 11:30 am
Till Eulenspiegel
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Under chassis view of the amplifier.

5 10amplifier 3

 I reckon I can get this amplifier working today.   Note the tidy heater wiring.

Till Eulenspiegel.

 
Posted : 09/02/2020 2:04 pm
ntscuser, PYE625, ntscuser and 3 people reacted
Till Eulenspiegel
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Progress report.    

As one would expect the coupling capacitors between the phase splitter stage and the grids of the EL84s are leaky so these will be replaced.  Also, it's most likely the 0.1mfd decoupling capacitor connected between the grid and chassis of the ECC83 will need replacing.  The HT surge resistors to the anodes of the EZ81 were anchored to spare pins on the valveholder.  These resistors have been removed from the tags because the Mullard data for the EZ80 and EZ81 informs us that the  pins are used for internal connections.

5 10amplifier 4

I've given the HT line a taste of electricity in an attempt to reform the electrolytic capacitors. 

Till Eulenspiegel.

 
Posted : 09/02/2020 4:41 pm
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Till Eulenspiegel
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News Flash!   It works.  Having established that the HT line is capable of withstanding slightly more than 300 volts it was time to connect the amplifier to the mains sans valves.  Sure enough 310-0-310 volts was measured on the secondary of the mains transformer.  The two 6.3volt heater supplies are also OK.  Next, connect up a loudspeaker.  Plug in the ECC83 and EL84s, heaters are glowing, let's go for it and plug in the EZ80 HT rectifier.  No bangs or flashes. A very faint hum can be heard from the 'speaker.  300 volts on the anodes of the output valves, 100 volts on the anodes of the ECC83 phase splitter.  Plug in the EF86, now things are happening.  With no input source connected the usual hummyness, refit the chassis bottom plate, hum almost gone and only a faint hiss can be heard.

Tomorrow I'll connect the amplifier to a much better loudspeaker and the Eagle FMT640 tuner. Will report the results.

Till Eulenspiegel.

 
Posted : 09/02/2020 10:52 pm
PYE625, Nuvistor, PYE625 and 3 people reacted
Nuvistor
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You said it would be working today. ? 

Frank

 
Posted : 09/02/2020 11:02 pm
Till Eulenspiegel
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Hi Frank,   with a little more work this will be a truly excellent amplifier. A number of resistors are out of tolerance and will be replaced.  More attention to screening around the grid circuit of the EF86 should reduce the hum level even further.  

I've another Mullard amplifier to look at, a 3-3. Will introduce it in a separate topic.

Till Eulenspiegel.

 
Posted : 09/02/2020 11:28 pm
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Katie Bush
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@pye625 I always thought it had to be yellow print, Blackburn codes, and manufactured before 1964?

Then again, I suppose if it were blue print, and the code was 999, then that would mean the 'ambliance' would be outside the door?

 

 
Posted : 10/02/2020 8:35 pm
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PYE625
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Valves are like wine....the greater the vintage, the better they are. ? 

 

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 10/02/2020 9:17 pm
Katie Bush
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Posted by: @pye625

Valves are like wine....the greater the vintage, the better they are. ? 

 

You missed one crucial detail - The more expensive they become!

 

 
Posted : 10/02/2020 9:37 pm
Till Eulenspiegel
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Gave the 5-10 amplifier a good test today, excellent results. Now I will explain why the amplifier was overhauled.

Recently I carried out a reconstruction of the amplifier chassis in the RGD 1046 radiogram.  PX4s replaced with KT66 or 6L6 beam tetrodes. A "Williamson" type of output transformer replaces the original burnt out part.  The 'gram itself now has a Goodmans Axiom 10 loudspeaker.  The amplifier is the later type with the tone controls in the negative feedback loop.

 So with all these worthy modifications one would expect the sound quality will be wonderful, in fact it is horrible. So in order to confirm that it's not the 'speaker for the poor sound reproduction the 5-10 amplifier was connected to the radiogram. Excellent sound quality coming out from the Axiom so now we know it is the modified RGD amplifier for the poor sound quality.

Till Eulenspiegel. 

 
Posted : 10/02/2020 10:24 pm
Till Eulenspiegel
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The RGD amplifier.

5 10amplifier 1046G

 

 
Posted : 10/02/2020 10:33 pm
Nuvistor
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What do you think is wrong with the modified RGD amp?

Frank

 
Posted : 10/02/2020 10:50 pm
Till Eulenspiegel
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Hi Frank, I think the first thing to do is remove the NFB tone control circuits. The sound the amplifier produces is like an off centre loudspeaker.

Till Eulenspiegel.

 
Posted : 10/02/2020 11:34 pm
Katie Bush
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Posted by: @till

The sound the amplifier produces is like an off centre loudspeaker.

Till Eulenspiegel.

Hi David,

It's interesting you should say that, but I recall many, many years ago, a similar thing with an amp using 6V6 beam tetrodes. It turned out that the output transformer had fried and suffered several shorted turns on its primary. I doubt that's the case here, but just thinking out loud.

 
Posted : 10/02/2020 11:47 pm
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