EL 6420

Burns, Selmer, WEM, and more

EL 6420

Postby Racing on Sun Jul 05, 2015 9:38 pm

As some of you know i´ve been down the road of old Philips amps before.
Well. This time we upped the ante a bit.

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I´ve always had a weak spot for these design wise. Early -50s n made in Holland. A rated output of 70 watts clean through a pair of EL-34,and seing they are run on the jagged edge at about 800 volts..no wonder.
The design tho is outta this world to me. It is just downright amazing.

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Yup. See that there protruding in the middle is an old EM-34 "magic eye". In short sort of a VU meter for those not in the know.

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This there in turn maybe not the sexiest side of the amp,but the signals need to enter and exit somewhere i guess.

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´N yeah. This is a toob amp see. Then please have in mind that two of them are hidden from plain sight by the pair of EL-34s.

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This in turn is just cute in my book. Seing the number of tubes onboard Philips in their wisdom setup these small signs to tell what goes where. As a whole we´re talking old rimlock EF-40´s and ECC-40 here. Tubes that i´ve played around with for guitar use previously with great success. For some reason many builders focus all their power on amplification rate n...to my findings there´s simply no need seing the amount of stages involved. One can get the signal to go into orbit no matter... Ergo,tone is of WAY greater importance. At least to me.

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Out rear. What can i say? :urawk:

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Ah. The EM-34. That thing that says peekaboo through the hood of this thing. Right. Hood. See,both the chassis and the hood are cast items. Not from detroit wondermetal thank god,but more so lightweight aluminium. That doesn´t tell the whole story though,cause light a 6420 is certainly not...

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...and some of that gets explained right here. Just LOOK at the size of that powertransformer! Drop that on your foot and say goodbye to it!

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Albeit being made in Holland at the time the amp was certainly intended for Swedish sales from day one. Hence all the labels asf are in Swedish.
Less common then you´d think as Philips at the time had factories all over. Scandinavia included.

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So. Underneath what greets us is this. Plain sheetmetal i guess..

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..that removed in turn. Order,to a degree i guess,but as "usual" with older Philips amps total chaos when it comes to the actual wiring.

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´N i guess this is where crap turns hot. :mrgreen:

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This in turn then the rather crude shield for two of the inputjacks. As you can see the actual jacks are of an older standard.


Well. Phase 1 will be to clean the thing out and check condition of e-lytes and what have you not. One issue with these older Philips amps is their black coloured wax coupling capacitors. They´re that old by now that there´s really no reason to even test them,they ALWAYS leak like crazy. Every single one of them,and hence these will be replaced before i even think about throwing the switch on this thing.

The two stock AX-50 mercury rectifiers (the amp holds 4 rectifiers in total-all of them tubes)has been replaced by AZ-50 ones. For the better really as the whole mercury thing might be beutiful to look at as they heat up but...in this case this amp will,as might be suspected,see new life as something way more contemporary sounding and..thus practicality is everything and there the AZ variety rectifiers simply are more safe.
First up tho..getting the thing to run.

As for the involved setup for the powertubes,seing the voltages at hand asf and in turn the rather intricate setup around their cathodes...i´m still undecided as what to do. Time will tell i guess.

That said. That there is one SERIOUSLY cool amp. To the point where the cool gauge needle about bottoms out and falls friggin off..
Racing
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Re: EL 6420

Postby trobbins on Mon Jul 06, 2015 8:05 am

That skin is fantastic - what a standout in the crowd!

At least the EM34 won't get cold, nor will the two little fella's tucked in cosily behind the EL34's .
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Re: EL 6420

Postby Vortexion on Mon Jul 06, 2015 8:29 am

I know it's got a whole lotta ventilation goin' on, but IMHO it's still amazing that the plastic cover has remained in such good condition with no discolouration, considering the heat it's had to deal with.

Yet another must-read thread, Racing! :thumbsup:
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Re: EL 6420

Postby Baron Von Machinenmann on Mon Jul 06, 2015 12:16 pm

Ah. The EM-34. That thing that says peekaboo through the hood of this thing. Right. Hood. See,both the chassis and the hood are cast items. Not from detroit wondermetal thank god,but more so lightweight aluminium. That doesn´t tell the whole story though,cause light a 6420 is certainly not...


:cheers:
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John Lennon/Jimi Hendrix/Jimmy Page Fan
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Re: EL 6420

Postby PeterS on Mon Jul 06, 2015 12:20 pm

plastic cover


I think it's metal.

That thing is awesome. At first glance I thought it was a little radio... I love the little signs with the tube numbers. I wonder if they did it that way so it could be changed without having to change the screenprinting of the entire chassis...
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Re: EL 6420

Postby Vortexion on Mon Jul 06, 2015 1:09 pm

Metal. Right. That would make more sense. :lol:
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Re: EL 6420

Postby Racing on Mon Jul 06, 2015 8:19 pm

Yup.
The cover is out of cast aluminium too.

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Right. Coupling caps. These are NOT something to hold on to. Fugedaboutem. A few of them were even cracked. This is not something to dwell on,if you run into these..replace. That simple.

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So. Coupling caps replaced. Didn´t cut the legs down as topology of the amp will be changed anyways all said and done,but this way i got it up and running at least.
Still doesn´t sound all that hot, but then again...could be attributed to about anything,down to busted pots. I installed a tele inbound and one outbound for this..temp style.

Checked the e-lytes with one of my ESR meters,and for the better as one of them "tower" e-lytes indeed was shot to kingdom come. Installed a fresh one in a REAL temp manner just to get the thing going.
Indeed,work it does. As it comes to settle in runs a B+ of approx 745VDC in 245VAC mode. Good enough,all of the tubes do fire and the thing has got sound,at least,coming out of it.
What that means is that transformers et al is all good to go.

The little things were given the light of day. Like pilotlamps and what have you not. Sorry to say that fanfriggintastic EM-34 was shot,as was one of the EF-40´s,but a fresh EM-34 is already in the mail so...

Been giving this with the mercury AX-50´s that the amp is SUPPOSED to sport some thought and...the AZ rectifiers stay. However..think i´m going to get me a pair of AX´s as i want to experience them mercury rectifiers first person. Have never dealt with them thus far...
The busted EF-40 is of lesser importance to me as i never use them upstream of a given chain..and there´s still two of them up and running which suffice for my needs and then some.

Then. The amp sports tube rectifiers ONLY. That means that the bias setup is running that way too,and i for one see no reason for that what so ever. In that app silicon is the way to go,as is implementing adjustability.
That much for the AZ-41 for the bias circuit... The other is the EZ-40 that is mainly used to power the "limiter" setup of the amp. Undecided what to do with that so far. Time will tell i guess.

One very profound reflection/impression is how silent the amp turned out to be in idle. Please have in mind that all i´ve done this far is replace ONE e-lyte,and in turn all of the coupling caps.

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That said. Here we go. Up and running. :D
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Re: EL 6420

Postby Racing on Sat Jul 11, 2015 5:35 am

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Well. If nothing else i can always say i´ve got an amp that turns green when i whip it. :mrgreen:
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Re: EL 6420

Postby Racing on Sat Jul 11, 2015 11:24 am

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That gentlemen is how a fresh,working,EM-34 looks.
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Re: EL 6420

Postby Racing on Mon Aug 03, 2015 10:11 am

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I´ll tell you what. That there is one SERIOUSLY sized main filtering cap! It´s of 16uF!
The tube next to it is a regular ECC-83/12AX7

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Same tube,just in this case next to the power x-former. This amp sport some serious dimensions of stuff onboard!
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Re: EL 6420

Postby DitDatVanAllesWat on Sun Nov 29, 2015 8:07 pm

Found this post while googling as I have a pair of these I am currently restoring.

Great post on a great amp. I will be following the progress closely on this one.
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Re: EL 6420

Postby Racing on Sat Dec 05, 2015 3:20 pm

Thanx.
Yeah. I guess we´ve reached upon the point where i need to get my ass in gear with this one again.
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Re: EL 6420

Postby DitDatVanAllesWat on Sun Dec 06, 2015 5:20 pm

I also have not worked on mine for the past 2 months or so. Will try to get back to them during the
winter.
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Re: EL 6420

Postby Merl1n on Thu Dec 10, 2015 1:01 pm

Hi

I have also one of these amp under restoration. That filter capacitor is certainly serious sized one. Is it really just 16mF/500V? Could it be replaced with one of those modern 16mf/500V caps which are far more moderately sized. I suppose there will be some extra space available after discarding that monster of a cap. Is there any reason why not to replace it with something for example 100mF/500V for more oomph in the power stage.

Best regards

-Merl1n
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Re: EL 6420

Postby trobbins on Sun Dec 13, 2015 5:50 am

Does the amp have a delay relay for rectifier warm up?

The big old caps are best tested with an insulation resistance tester (as used by electricians for cable testing) - if they pass muster then I reckon the aesthetics are good (it may also be irresponsible to pull them out and put them in the trash, as a lot of them contain pcb oil).
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