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Old 13th Jul 2017, 3:18 pm   #1
barnabe42
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Default How to setup EL6400 with loudspeaker?

Hello,

I found an amplifier EL6400 with 2 loud speakers that I would like to restore.
The issue is that I don't really know how to connect them together, I could find some documentation regarding the amplifier but nothing about the loud speaker.

futhermore the loudspeaker manual are in Dutch ....

The amplifier is set at 100v output.

In both loudspeaker I have a transformateur that is not connected , Can I find any documentation of to wire it ?

The amplifier is mono so the loudspeakers are plug in parallel.

Can I plug dirrectly the loudspeaker on the amp ? is the transformer needed ? the loudspeaker at composed of 4 el7011 in series the impedance is about 17 ohms.

Anyhelp would be appreciate as I am scared to plug the loudskeaper directly to the amp without any knowledge ...

Thanks,
/Eric
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Old 13th Jul 2017, 4:35 pm   #2
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Default Re: How to setup EL6400 with loudspeaker?

To aid anyone able to assist the OP, the circuit can be found in this thread:-

https://www.vintage-radio.net/forum/...ad.php?t=99021
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Old 13th Jul 2017, 4:59 pm   #3
ColinTheAmpMan1
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Default Re: How to setup EL6400 with loudspeaker?

Hi,
I have a friend who used to be a physics technician at a University and also is a bit of a student of Dutch. I might be able to get him make some kind of translation of the manual in Station X's post. If you have the speaker manual as well, he might even help with that. It will cost me a beer or two, I'm sure.
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Old 13th Jul 2017, 6:00 pm   #4
Edward Huggins
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Default Re: How to setup EL6400 with loudspeaker?

I remember the launch and subsequent promotion of this. It is primarilly designed as a PA amp, but will give a reasonable mono sound on the "Gram" channel using a crystal/ceramic cartridge of about 150mV. These were never designed to be used with MMs. The default wiring of these speakers is usually 100V. There are good quality drive units with good powe handling. However their suspension will be stiff and and are optimsed for speech rather than music. Maarten will certainly know more!
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Old 13th Jul 2017, 6:32 pm   #5
qualityten
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Default Re: How to setup EL6400 with loudspeaker?

I read Dutch and this is a pretty basic description of the amp. For use, looking at the numbered diagram, with the unit unplugged, lift the connector at 2 and rotate it so that you select the correct mains voltage (presumably 200-250V for Finland). Lift and rotate plug 3 to set for the speakers, depending on their output impedance. You may have to describe how your speakers are connected so that we can help you choose the right impedance.

Use the chart on p4 of the manual to select the right speaker impedance. For example, for common modern speakers of between 15 and 8 ohms, use the 25V connection, and for 4 ohm speakers use the 10V plug. The manual says that the 10V connection is used for connecting to headphones or low impedance speakers, or to use the amp as a preamp. So, the 25V connection should be okay for a combined impedance of 17ohms. BUT, there is another transformer in the cabinet, which I think might be for converting 100V line outputs for low impedance speakers. Perhaps someone else can advise on this.

The speaker plug is marked as 5. The earth/ground connection is the Right hand pin.

Last edited by qualityten; 13th Jul 2017 at 6:51 pm.
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Old 13th Jul 2017, 7:32 pm   #6
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Default Re: How to setup EL6400 with loudspeaker?

One of the valves has gone white indicating it has lost its vacuum.
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Old 15th Jul 2017, 2:16 am   #7
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Default Re: How to setup EL6400 with loudspeaker?

It seems the loudspeaker box has a built in 100V transformer.
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Old 15th Jul 2017, 11:10 am   #8
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Default Re: How to setup EL6400 with loudspeaker?

Thanks Maarten. So, the 100V setting on the amp is the right one for output to the 100V transformer. I guess it's safe to assume that the speakers are matched to the output of the transformer.
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Old 15th Jul 2017, 12:05 pm   #9
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Default Re: How to setup EL6400 with loudspeaker?

It looks to me like the power taps from the 100V Line Transformer go to some kind of socket, but is there a plug in that socket? Or perhaps the knotted red wire goes to a wander plug?
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Old 15th Jul 2017, 1:36 pm   #10
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Default Re: How to setup EL6400 with loudspeaker?

Hello,

I set the voltage to 25V and replace one preamp valve.
I got it started and I can heard some music.

The only issue right now is that I get a huge hum through speakers.
What could the reason be ? I have spare valve so I will try to replace the them.

The loudspeaker box have a built in 100V transformer would that reduce the hum if I use them ?

As I understood the 100V are just used if the connection between the amp and the loudspeaker box is in tenth of meters.
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Old 15th Jul 2017, 11:03 pm   #11
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Default Re: How to setup EL6400 with loudspeaker?

Can you try connecting the amp separately to a standard 8 ohm speaker? This would check if the problem is with the amp or the speaker connections.

If the hum is still there, I would guess that the hum is caused by dried out electrolytic capacitors in the power supply of the amplifier. See C12 and C13 (two 25uF capacitors in one can) and C14 and C15(two 50uF capacitors in another can). If there is a hum and you replace them, check the voltage rating necessary on the capacitors themselves. Replacements need to be the same voltage or greater, but can be similar in capacitance, e.g. 22uF for 25uF and 47uF for 50uF.
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Old 16th Jul 2017, 8:00 am   #12
barnabe42
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Default Re: How to setup EL6400 with loudspeaker?

Thanks for the guidance, I tried with an 8 ohm speaker and I got same result.
It seems hard to find those CAN capacitor, can I use standard electrolytic capacitor 400V side by side ?
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Old 16th Jul 2017, 5:58 pm   #13
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Default Re: How to setup EL6400 with loudspeaker?

Before replacing the capacitors it is worth performing a few tests:
Does the hum increase with volume?
What are the anode and grid voltages of the output valves?
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Old 16th Jul 2017, 8:11 pm   #14
barnabe42
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Default Re: How to setup EL6400 with loudspeaker?

The hum is fading when increasing volume.
I will study the anode and grid voltage I am not really familiar with those .
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Old 17th Jul 2017, 9:47 pm   #15
qualityten
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Default Re: How to setup EL6400 with loudspeaker?

Quote:
Originally Posted by barnabe42 View Post
Thanks for the guidance, I tried with an 8 ohm speaker and I got same result.
It seems hard to find those CAN capacitor, can I use standard electrolytic capacitor 400V side by side ?
If you find that you need to replace the capacitors, yes you can replace them with individual ones side by side. Or multisection capacitors are available from specialist suppliers, e.g. https://www.watfordvalves.com/produc...subsub=&page=2. You could probably use either the 16/16 or 32/32 to replace the 25/25uF.

The anode at the top cap of the EL81 valve, but you can measure the voltage where the wire goes from there to the transformer. Measure the grid voltage at pin 8. With a multimeter set to AC, the black probe touches the metal chassis, and the red probe to the measurement point. Neither should be above 250VDC.

Last edited by qualityten; 17th Jul 2017 at 9:59 pm.
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Old 17th Jul 2017, 10:46 pm   #16
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Default Re: How to setup EL6400 with loudspeaker?

'spot the mistake!' 'with a multimeter set to AC the black probe touches the chassis, and the red probe to the measuring point (i.e either the anode or the (screen)grid of the EL81. Neither should be above 250vDC!!!
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Old 17th Jul 2017, 11:22 pm   #17
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Default Re: How to setup EL6400 with loudspeaker?

If the hum is changing with the volume or tone controls it is possible the problem is not with the electrolytic capacitors.

The volume control is very unusual as it is off in the centre position and increases the volume from the pre-amplifier in one direction and from a different socket when turning in the other direction. The pentode pre-amplifiers are triode wired but running at full gain and have a very high input impedance so they could easily pick up hum.

I would try with the 2 pre-amplifier valves removed.
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Old 19th Jul 2017, 8:24 am   #18
barnabe42
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Default Re: How to setup EL6400 with loudspeaker?

Hello,

I measure the both anode on EL81 and I got 55 and 35V when nothing connected in the inputs.

I removed all the EF86 and then the hum was huge.
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Old 19th Jul 2017, 9:30 pm   #19
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Default Re: How to setup EL6400 with loudspeaker?

That implies there is a fair amount of ripple on the HT supply.
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Old 20th Jul 2017, 11:04 pm   #20
qualityten
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Default Re: How to setup EL6400 with loudspeaker?

Quote:
Originally Posted by 'LIVEWIRE?' View Post
'spot the mistake!' 'with a multimeter set to AC the black probe touches the chassis, and the red probe to the measuring point (i.e either the anode or the (screen)grid of the EL81. Neither should be above 250vDC!!!
Well spotted! .

p.s. Barnabe42: If you do replace any electrolytic capacitors, it is essential to get the polarity right.
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