Author Topic: Philips EL6411  (Read 9398 times)

Offline Qualityten

Re: Philips EL6411
« Reply #15 on: October 12, 2015, 11:17:20 PM »
Thanks Mars.  :thumbs:

Offline Qualityten

Re: Philips EL6411
« Reply #16 on: October 15, 2015, 10:13:37 PM »
I've returned to my amp like this over the last few days.  I also removed the EF86s, volume and tone controls.  This also removes the hum problem it had before!

With a line level input from a CD player into just one ECC40 as phase splitter, there is not much volume.  If the input goes in before C10 to the 2nd grid of the first ECC40 it is plenty loud.  Of course this is still with the original PPP arrangement, and only mono, whereas stereo would be more useful.

Mars, do you have enough volume with the CCDA 6SN7 preamp as driver?

Offline Mars

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Re: Philips EL6411
« Reply #17 on: October 19, 2015, 06:20:09 PM »
I injected the signal just after C11 on the grid of B4. You do not need a capacitor - just go directly to grid. I get plenty of volume from my soundcard :groovy:

Here's some pics:







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Offline skollie

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Re: Philips EL6411
« Reply #18 on: October 19, 2015, 11:11:21 PM »
Hi Mars

Your pics are a delight to view :clap:

Regds

skollie
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Offline Qualityten

Re: Philips EL6411
« Reply #19 on: October 22, 2015, 12:22:20 AM »
Mars, thank you very much for taking the trouble to post these detailed pics.  I've been away for a couple of days, so have just seen them.  They will be really helpful.

As Skollie says, they are also reflect beautiful work.

Offline Mars

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Re: Philips EL6411
« Reply #20 on: October 28, 2015, 03:59:34 PM »
Even more pics to look at :whistler:






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Offline Qualityten

Re: Philips EL6411
« Reply #21 on: October 28, 2015, 08:31:46 PM »
Thanks again Mars.  Your new layout is really elegant. 

I hope this will also inspire others who might be wondering what to do with one of these Philips PA amps.

Offline Qualityten

Re: Philips EL6411
« Reply #22 on: October 30, 2015, 09:23:00 PM »
I've been doing my own version of the rebuild.  And attach a pic of the chassis from below. The rewiring is almost complete, but I have one pair of wires from the power transformer spare!  I have ringed them in green in the PT picture, and in the chassis overview.

My wiring from the centre tap (brown wire) via the 39ohm resistor, goes in parallel to the four 100ohm resistors to grid 2 of each of the EL81s.  Mars' yellow and white wiring to the same resistors goes separately to each.  Is this just to avoid hum?  Do all four wires also go to the PT centre tap, or my spare connection?  Mars, a picture of your PT secondary wiring would answer my query.  (I know I should have marked each wire when I disconnected it!)


Offline Qualityten

Re: Philips EL6411
« Reply #23 on: November 01, 2015, 09:45:49 PM »
I've got on with installing the output transformers and the amp plays nicely. BUT the bias wiring is not right and the anodes glow red very quickly.   :thinking:  I'll sleep on it.

Offline Qualityten

Re: Philips EL6411
« Reply #24 on: November 02, 2015, 07:17:36 PM »
I've decided to untangle the multiple wiring from the power transformer to make sure that I've got each winding wired correctly.  It's amazing what a little thinking time can do.  :)

My apologies to Mars if my efforts to copy his work have taken over this thread.  I've kept the posts here as I wouldn't have thought of this without his example.
« Last Edit: November 02, 2015, 07:19:52 PM by Qualityten »

Offline Qualityten

Re: Philips EL6411
« Reply #25 on: November 03, 2015, 12:37:51 AM »
I found my fault: I forgot to ground one side of the bias circuit.  It's working well now.  I'll post a completed picture once I've tidied up the bias wiring.

This is not the loudest amp I own, but it is more useful as a stereo hifi power amp than a mono PA amp.  I bet it sounds great with Mars' output transformers!

Offline Qualityten

Re: Philips EL6411
« Reply #26 on: November 05, 2015, 01:12:55 AM »
As promised here are a couple of pics of my 'finished' build.  Finished is in quotes as the output transformers aren't matched and there is a difference in volume between the channels.  The bigger output transformer is made by Vortexion.  I have another big OPT that I intend trying in place of the smaller one.  All are ultralinear, but I have not connected the screen taps.  That is also the reason for the tags on some wires.  I don't want to forget which connects to which.



I see that marking the speaker sockets L and R from upside down puts them the wrong way round...



Thanks again to Mars for his help.

Offline fredeb

Re: Philips EL6411
« Reply #27 on: November 05, 2015, 06:34:43 PM »
So ...... What does it sound like ?

Well done ! While I'm at it .  :thumbs:
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline Qualityten

Re: Philips EL6411
« Reply #28 on: November 06, 2015, 01:03:42 AM »
Thanks Fred.  It sounded very clean and fresh, if that makes sense.  More clinical, little tubey warmth.  What impressed me most was that the amp was completely quiet.  No hum at all.

Until I replace the smaller transformer with a bigger (higher quality one).  This has roughly the same volume as the Vortexion one and so there is good sound balance and enough volume with sensitive speakers.  But the channel with the replacement transformer now hums softly.  It's not bad, but it's not dead quiet anymore.  Moving amp around while replacing the transformer also caused a resistor to short and burn.  I fixed that and then reassembled the chassis, only to find the hum! I think it is because the new output transformer is too close to the power transformer, but I don't recall the hum before the bias resistor shorted by touching a ground connection.

I find this often happens with amateur amp building.  I can do the basics, but secondary issues have to be solved afterwards.

I should say with the two bigger output transformers, it sounds very good indeed.  That clear, real valve sound is the hook that keeps me on the quest for more and better.

Offline fredeb

Re: Philips EL6411
« Reply #29 on: November 06, 2015, 09:25:15 PM »
I'm trying to gain an understanding of how this all works myself . I suppose the only way is to try and try again , learning from one's mistakes and paying attention to what the knowledgeable folk have to say . By now I wish I started doing this when I was 16 years old , it's such a vast field .  :thinking:

ATM just trying to build an existing design is challenging , nevermind trying to design a circuit myself .

Do you think you may find some better transformers down the line ?
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts