Italian tubers

Burns, Selmer, WEM, and more

Re: Italian tubers

Postby Racing on Tue May 29, 2012 11:29 pm

Yes Sir. Sure did and IMO the reverb n tremolo are good,i´ll give you that,however the basic tone of the amp is so dull it is beyond watching paint dry.
No offense but IMO a FBT500,no matter the bass/organ version or the two channel trem/reverb unit,when overhauled(caps aso) is stiff and lifeless beyond words.
Child of it´s time? Yup. Still dirt cheap and good solid basis to build a true rocker out of.
In fact,one of the few amps even worse to me is a 250. With those 75VDC at the anode nothing good WILL come out no matter if i put it into orbit.

Agree with you on the EL503s tho. Marvelous pieces in my book.

FWIW if "major surgery" isn´t your thing just try putting a 470k resistor on the grid of the concertina. That´s it and that´s that. What that buffer will bring is that it´ll smoothen out that rather jagged and ugly sound from the PI when overdriven. It really works and it works well. It won´t affect anything else than that. In short you´ll get a better sounding amp as you push it-at least what´s there to push in OEM form :mrgreen:

On a different note not ONE of those i´ve dived into has been biased anything even CLOSE to nominal. A set of "bias resistors" and an according bias adjust can perform wonders from many respects to my findings.
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Re: Italian tubers

Postby dread_lion on Thu May 31, 2012 9:35 pm

Hey Racing,

Thanks for your input. I will check out that resistor mod on the phase inverter!
What DO you bias those tubes at then? i'm intrigued :p I'm usually really carefull about biasing, especially when working with oddball tubes, as i dont have enough experience to go mad on those things, and risk blowing up tubes. Also, not a lot of people have experience with el503's, so i'm really looking forward to what you would suggest ;).
Personally, I tried this amp on different speakers, and i must say that when pushing non-efficient speakers, and overdriving the amp, i didnt like the sound either. As you said, harsh and very, very dull. But on more efficient speakers, running purely clean, i really digged that amp, very clear and pronounced with a deep bass. just looking at it, i allready figured this amp wasnt designed to make any kind of smooth overdrive, so i guess i have to agree on that!
But did you like the clean sound at all before modding? or did you find that boring too?
vintage baby
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Re: Italian tubers

Postby Racing on Sat Jun 02, 2012 12:37 am

You can bias those EL503s to an easy 20w/piece in idle. No worries what so ever. In fact,as the spawn of EL34s they are from every aspect simply more up to snuff tubes. If n when you check it out expect B+ to dial in at a rather precise 400VDC+. Ie;404-408VDC under load. Also mark that there´s a "sugar lump" mounted within the powerstage chassis where you can opt to hook up for 240VAC/socket which i recomend if you haven´t already.
Also check the 220k anode resistor for the concertina driverstage closely. Check to see if the value of it has drifted and check for discolouration of the resistor.

Further replace the 4700pF feedback caps for the powertubes as due routine. Just do it...trust me as those caps are the No1 issue for failure with these amps.(They run in series with a 15 Ohm ceramic resistor each). In fact,before replacing these you won´t be able to "lean" on the amp with confidence...just trust me on this. This regardless if they check ok or not.

Cleans then.
The 500 and the 250 are two vastly different animals. IMO much can be set for the voltage delivered to a preamp. The 250 indeed lacks in this dept with it´s mere 70VDC+ on the first anode. That voltage simply renders the capacity of swing for the anode brutaly lacking. Ie;there needs to be ample voltage,regardless of anode resistor size,to cater to anode voltage swing. If not there´s simply nothing to work with.
The 500...ain´t as cripple´d from that respect. However,the rev n tremolo setup is still just a 2 gainstage affair and as such...pushed the way it is...TBH i don´t think so (as far as sounding good in clean),but that is more of an opinion on my behalf than a fact.
In general,having fooled around with tube amp design over the yrs,i opt to set the 1st gainstage up with a 150k anode specificaly to cater to swing and thereby headroom when there´s enough B+ to work with. Likewise IMO very much can be had as far as "warmth" and presence by altering cathode resistor value-again dependant of available voltage.
For "dirty" work i often seem to end up at 300VDC+. For cleans...have those 150k in mind,i more often than not seem to touch down at the other end of 330-340VDC for the first stage.

Yes. The concertina phase inverter has quite a rep of being "difficult",as does the paraphase et al. I for one find that a load of.....cause as with anything else it comes down to understanding the parameters at hand and the cathodyne/concertina can be had to work beutifuly for overdrive as long as you accept what needs to be done.
For the actual catho....first of all for some reason i ALWAYS end up using a 3.3k cathode resistor before the negative side resistor of whatever value the concertina is setup for-be it 33k/33k,47k/47k or 100k/100k. Second of all,and this is imperative,i to the letter without exception ALWAYS ad a big fat gridresistor as a buffer which serves to buffer the signal enough to get rid of the rather jagged wave form which the concertina is rather infamous for to produce when in overdrive. That last buffer will take care of that and is a VERY well worth modification even for a stocker as most tube amps CAN be driven into at least crunch mode,in which case said buffer will work WONDERS. Just trust me if you don´t have a scope at hand. Try it...it´s easy enough,and at the PI the AC signal is lively enough not to care all that much about resistor value anyways. 470k and up does it and the actual amount comes down to how much you wanna tame the treble of the amp in case down IMO. 470k is minimum to see the effect of it though.

As for these amps as a whole you IMO have to take to heart that they are the spawn of a different time n age. Although Hendrix et al where all the rage at the time...Italy was a far way...and as such...these amps weren´t designed to work in overdrive. They were designed to cater as "instrument amps" more than dedicated guitar amps,which figures....
In short...as with the Dynacords of the time asf much can be had from minor "adjustment work" in my book. I´m NOT here to say that what i do caters to everyone. Not for a friggin second even. That...is just me,but besides that...many minor mods can be done to these amps to guitar or bass "dedicate them" in as much that the mods can be reversed and the beuty of the mods being that all in all they´ll just make the amp more contemporary sounding while still LOOKIN old.
The thing here is to take to heart that for a guitar oriented sound a two stager(which the stock unit is) can be ample signal enough to produce a coarse overdrive a´la early Fenders and lust to experiement is the key.
Take to heart that the LOWER the available voltage...the easier the stage in case will go into orbit while at the same time maximizing headroom and "livelyness".
In short the amount of amplitude is one thing..and this needs to be kept in check vs the voltage available. The higher the actual voltage the more "direct" and the harsher the amp will sound. Vis a vi...the other way around.
VERY VERY VERY much can be done with a mere 2 stages. Just look n listen to a simple Pro Jr. Two stages...with an attitude.

TBH tho..no. I don´t find the OEM FBT clean channels especialy well sounding in stock form. Like stated the trem and the reverb are above average IMO but the basic tone of the amp sincerly lack out in my book. MUCH can be done by replacing a few resistors and lytes in my book. Indeed the two stages of each channel is kind of set up "socialistic gray" if you start to scrutinize the whole package.

As a starting point,if you wanna keep with the OEM 2 stager,try replacing the OEM 100k/1.5k of each entry stage...replace that wth 150k/3.3k or 2.7k and a lyte of 2.2 to 4.7uF. No need for lytes any larger than that for overdriven guitar use in my book as a guitar has no business any lower in frequenzy anyways.
But that mod alone will ad TREMENDOUS amounts of warmth to a 500.

To cater to two stage overdrive,as the preamp is served generous amounts of voltage OEM anyways,play around with the last voltage divider resistor of 10k/5W. Err on the big side and take to what the alterations bring. Ie,replace with for instance a 22k and see if that is to your liking. As for the 5W spec...just forget about that. The "D" outlet serves all in all 2 ECC83,s and as such a mere 1watt will suffice just fine.
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Re: Italian tubers

Postby Racing on Thu Jun 21, 2012 7:31 am

Old friend and fellow guitarist D-drop stopped by with the innards of an ol´ beat up DNS 30.

I´ve come to understand that these old DNS machines where marketed through the rest of europe under the name "sound". The scandinavian importer being Albin Hagstrom of Sweden (Yes...Hagstrom guitars in Alvdalen) relabeled these el cheapo italianos to DNS up here tho for "Denmark,Sweden,Norway".

The amp was handed to me as a no-go,and that basicaly from old age. Where the FBT;s of the time are very sturdy built machines from top notch materials the DNS;s are not so much... :mrgreen:
In fact from many respects these DNS amps are a true educational experience in how NOT to do it. :lol: For instance the preamp is PCB based. A single layer copper mask that is..."questionably" bound to a fibreglass board and then suspended mid air through the pots soldered to it.
Weeeeeell...let me start by saying that the preamp board quality for one absolutely sux. As soon as you unbolt the thing from the faceplate (which in turn is a very thin aluminium sheet metal thingy)it´ll warp from here to kingdome come. Now...be that as it may the issue with that is that the coppermask isn´t exactly pliable rendering a copper mask that shows like a zillion microcracks.. :shock:
So. I basicaly hit the mask with soldering tin and some single strand wire just to make sure it could be relied upon as i dwelled on this little mini project on D-drops behalf.
D-drop asked me to pull one of my 4stage jobbies and then with the remark that it should all LOOK as stock as possible on the outside. The idea being that "he with the ugliest piece of equipment on stage wins". Mind you,this being a combo he´s already ontop as far as i´m concerned.

Anyways.
Modded the powerstage as far as the concertina asf per above and then remodeled the driverstage for it to work with a more contemporary ECC83 vs the OEM ECC82. Yes...i´m aware that the lesser "mu" of the 82 is supposed to minimize noise levels but from practical experience it kind of comes down to zero difference when setup right,and mind you this isn´t exactly hi-fi but a friggin guitar amp.

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OEM this is a twochannel rocket. Not so anymore as both onboard preamp tubes are used to power one 4stager since a few days back.

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A nifty little gift from the OEM designers back in the day is this little strand of plastic that was installed for some reason beyond me. Regardless...it has become kind of semi conductive over the yrs....n zee...that a bad thing with 360VDC ontap. :mrgreen:
Likewise the entire "mega lyte" in there....is rated at 350VDC...what WERE they thinking? Also please look at how the wires are basicaly pressed in place between the chassis and the PCB.

Going from a common 2 stager to a 4 stager places greater demands on S/N ratio and as such i opted to install a full set of 47uF 450V caps making sure that the grounding of the first cap vs the centertaps of the trafo was clear of anything else. Ie; the other caps were grounded otherwise,and this indeed made for a MUCH more silent amp in idle.

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As can be seen this is a simple twin EL84 P/P amp that was claimed to put out 25watts. Not in a million yrs with the OEM setup...but whatever i guess..
Seing the rather elevated voltages,having the EL84s in mind,one should be careful when selecting powertubes for these old rockets IMO. I use chinese rip offs of the old russian 6N14P which caters to the rather high voltages. Other more "common" EL84s might not.
Voltage drop is set to approx 13VDC across the cathode resistor for the pair.

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Preamp PCB was cleaned up considerably as far as amount of components and as such leaves a less clustered impression. As you can see there are two "dummy" pots left,and these are basicaly on there to keep the PCB to the faceplate for now. Need to reevaluate that before the amp is put into action again. Thinking along the lines of adding a couple of small simple L formed brackets to keep it simple.
All pots were shot (as a word of notice they are almost always shot on these amps due to poor quality) as were caps.

So. That´s where we´re at right now. Amp is up n running again,and as stated in 4 gainstage form. It produces a rather hefty amount of distortion at will and i still need to balance the various stages vs each other a little better. The OEM James tonestack is still intact and it might be that i need to adjust some of the values within there too.
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Re: Italian tubers

Postby Racing on Tue Jul 03, 2012 12:06 am

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...n here we go once more. This time out an old DNS 60RT that actualy WORKS. :lol: . No matter,it´ll be torn to pieces and built up again..."Racing style".
They´re still butt ugly tho... :thumbsup: . Even the tremolo is mismatched tbh. Way way way to fast in intensity to be of any good.

That said it looks like a fellow tubenut just let me score his DNS 120 tonight. From what i´ve figured so far the main difference,apart from estetics,being that it sports a pair of EL504s out back.
Going to be interesting to take deliver of that!
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Re: Italian tubers

Postby Racing on Wed Jul 04, 2012 10:01 pm

..and here we go. One basicaly,since tonight,higain old DNS SP60RT. Yeeeeep...even the reverb and tremolo are intact.

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Them a LOT of novals!! :lol: . Yep. Both the reverb and tremolo are tube driven.

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Have to say...this time out was a treat as the old warhorse was in such a nice nick rendering that what was needed was basic just replacement of key components and the modding per se. IOW as is it is a 4+1 stager. +1 counting the driverstage for the concertina.

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Yep. True that.
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Re: Italian tubers

Postby Racing on Wed Jul 11, 2012 10:55 pm

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Took delivery of the 120. Rocked to say the least. Tolex downright looks like crap and is full of torn bit n pieces.

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Preamp is basicaly the same two channel unit as to be found on the SP60RT above. Just that faceplate layout is a little different.

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After correcting some previous owners attempt of bias balance i opted to redo the whole thing and make the bias both adjustable and adjustable for balance. Point being that the previous owner was of the notion that a balance pot of 100k was just to be installed between the bisa voltage in and out. One leg towards each powertube,and done deal.
That was replaced with a 2.2k trim pot and a pair of "leak" resistors for ground,and as such the balance setup became operable.
The 100k pot was used instead of the bias circuits leak for a ground. Whole thing worked like a charm

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Major culprit though was the noval socket for the phaseinverter. PI in this case as with most other old italians being a concertina. Anyways,the noval was shot so this was replaced...and then i fired the thing up. Adjusted bias asf...checked the driver and concertina for voltages...and it all checked out. Done deal sort of.

When i hooked the preamp up it turned out that the reverb recovery stage had some funnies going on. This was eventualy traced to two things. First of all both anode resistors had drifted severly vs the schematic....and the second one i discovered as i hooked the unit up to play it.
It had a hum you wouldn´t believe.
This was traced to that the leg from the wiper of the reverbpot was downright mechanicaly broken-as in off. Repaired that in a jiffy...and we were good to go.

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One of this machines peculiaritys is that it uses EL504 powertubes. This being my first acquaintance with that powertube...i was again pleasantly surprised i have to say. Like its sibling the EL503 (which in contrast is a very expensive tube) it used the magnoval socket.

So. That said. What does it sound like? OEM...well at least more rocknroll than its SP60RT counterpart. But a full dressed rocknroll amp by MODERN standards it is not.
So i plan to pull "my 4 stager" once again and take it from there..
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Re: Italian tubers

Postby Racing on Sat Jul 14, 2012 6:54 am

Update time.
So.
The transformation came full circle and the old DNS turned into a 1 channel 4+1 stager alright.

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Various e-lyts and what have you not were replaced due course. Bias circuitry was remodeled to be adjustable both for amount and balance. The latter being half important as these old NOS EL-504s are rarely found in matched pairs. Solved that with a simple 2.2k pot which was hooked up to the 220k resistors running for the signal out of the PI and then set it up with a "leak" resistor on each leg out of the trimpot vs ground. Resolution made them end up at 47k,which in turn made it rather easy setting the two powertubes up in balance in idle.

A master was added. This was hooked up where the signal goes from the driver into the concertina. Two 100n caps were used to send the signal to n from the master via the novalsocket setup you see in the pic.(This is OEM btw.)

The 100n caps out of the PI were replaced by fresh 22n dittos. Again,the OEM polyesters used...are of questionable quality. They seem to interfere and break the sound up for some reason due to old age.?

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Master,a 1MA pot,was placed in what was the second channels jack 1. The second jack..recieved a midpot for the second tonestack.
The stacks of this machine are both James setups. The second one then only using a midrange resistor OEM so this was looked into. As is i´ve spent some time tossing the various values of both stacks around quite considerably. Point being that OEM they weren´t exactly setup to cope with distorted sounds,that much is for sure. So some of the values were changed quite considerably.

Yes. Both the tremolo and the reverb are intact. The trem works quite well IMO while i´ve had to spend some time taming the reverb down. No wonder if you take into consideration that the reverb signal is both sent and recieved between the 1st and 2nd gainstage.

A word on the cab for closing. Wear n tear is one thing...this tho....was rediculous. It is to the point where i´ll have to mill half and inch or so off the rear ledge just to clean the ledge up. Tolex...was more torn than anything else.
So. Cut and sand the cab a bit...and then for some fresh tolex and piping i guess.

One thing´s for certain. This old DNS has gotten a new lease on life,and then in a quite modified form. For the better as far as i´m concerned as now it can at least be used to produce rock with some sort of confidence.
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Re: Italian tubers

Postby Racing on Wed Jul 18, 2012 6:10 pm

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...n here we go. A now refurbished old DNS 120 Supreme that has gotten a new lease on life. Roaring away like it was the end of time...
Tremolo and reverb still intact and recalibrated to work with the much higher signal ratios.
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Re: Italian tubers

Postby Racing on Fri Nov 09, 2012 1:59 am

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Ran into yet another one,and this time as a complete rig. In rather nice nick to boot.
Transformed that into something way more contemporary sounding,and it is since sold. I can attest to that two of them EL504s out back being served what they need makes for one seriously loud amp (DNS/Sound claim 80w and i see no reason to disbelieve that). What´s more the sort of open back 112 boxes are stuffed with old RCF speakers,and these took to their new task like nothing i´ve ever encountered.
Anyone that runs into one of these dirt cheap rigs..bring it home with you. You will NOT be disappointed after some solderwork!!

Have built a number of amps in between,but today i went italian again.

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Yep. Yet another EL503 equipped FBT 500-R2.

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Downright fantastic powertubes,albeit expensive as they aint reproduced yet.

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As mentioned previously these amps are totaly PTP built and with minor exceptions out of high Q pts. Further they all seem to be biased ice cold from the factory at the time,and hence..readjusting bias to where it needs to be set really wakes these puppies up.
The FBT 500s are also good foundations to build something own out of.
As is though...both the DNS supreme and FBT 500 are about as fun sounding as it is to watch paint dry. Regardless..if you know what you´re doing they are absolutely fantastic foundations...
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Re: Italian tubers

Postby Racing on Fri Jan 18, 2013 11:15 am

Built yet another one....

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This one i converted to a longtailed pair phaseinverter. Worked and worked well.
In turn scrapped the burnt to smithereens reverb,but kept the trem. Modified the trem to work better with the increased gain capacity. Preamp this time is a 4 stager. Mastervolume and mid/gain structure controls added too.
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Re: Italian tubers

Postby Racing on Thu Jan 24, 2013 1:41 am

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Was handed this old DOA single end EL84 amp. Reason for it not working soon enough showed..the mains switch was simply full of crud. Cleaned that out..and the erosion on the fuses and fuse holders..and she was ready to go.
It sounded...
Bloody awful :mrgreen:

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Mainly,i guess,due to that speaker right there. It has to be the worst sounding speaker i´ve EVER run into! This..this strikes a new low boys n girls! DAMN that thing is lame! Shrill highs only,and in the worst kind of ways at that.

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One VERY tired RFT EL84. I suspect outpower to have been around 1-2 watts or so. None the less...two pcs of 83s/12AX7´s. The thing with that tho is that two triodes are used for preamp....one for trem...and then one is left to do...nothin.
While at it..just LOOK at that minescule little OT! ´N the beuty is the ink marking...."10w". Yeah.... :shock: :shock:

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This thing tho? What is it? For what was it conceived? It is by FAR the worst sounding speaker i´ve EVER run into! It should be outlawed even!

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A couple of hrs later though we had ourselves a board with components added...and replaced. Cathode resistor was set to 100 Ohms....and that last "left to do nuthin" triode was set to work like god intended.
To that..another two pots were added. Gain and master volume.

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Recycled a couple of old DNS knobs...and the whole thing was starting to come together. Come tomorrow i will replace that "multi" electrolyte with 3 pcs of radials..and take it from there.
...´n more important...replace that speaker. ANYTHING OUT THERE will be an improvement! What WERE they thinking??
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Re: Italian tubers

Postby Racing on Sat Jan 26, 2013 2:11 pm

For the final update on the "ten" then...

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Fresh components for everyone. In this case not the end of the world as the amp is rather simple in build. Believe i´ve touched on it before,but one major low quality point of the DNS/Sound amps as well as the FBT´s of the time is that the pots very often are downright crap. In this case too...so they got replaced as well.

http://www.102983.org/gallery/albums/userpics/10003/Schema.jpg

Guess someone down the line might have a need for the schematics of one of these,so..there ya go. The "Sound" labeled amp was called DNS(for Denmark,Norway,Sweden) up here in Scandinavia.

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The megaheffa e-lyte was replaced by these three. The funny tidbit in that is that it is the smallest of the three that carries the 100uF capacitance. Beside them is the heater balance trim pot.

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Some previous "Mr Handyman" had replaced the OEM 8" speaker with a broadband 12" Philips. Now...that might have been all good and dandy had Mr Handyman hogged out the baffle accordingly :mrgreen: . So...out came the cutter...and soon enough the hole was of apt proportions. At first i tried it with a VHT speaker i had laying around of 60w...one that i find has a lot of Cannabis Rex character to it. The rather limited power of this amp tho...nah..
So. Replaced that with a Jensen C12Q i had as a spare..and that was exactly what the doctor ordered!
That done i fabbed a solid fibre board back for the cab,and indeed. Way better.

Remains to dress that with some tolex i guess..

One minor issue remains though. The trem speed pot was shot so i replaced that one. The funny thing is that as i did,before...the amp went basicaly dead silent as you rolled volume off on the guitar,after the swap of said pot i´ve got this minescule hiss that enters from the trem circuit for some reason. Have tried pinning it down to no avail so far.
Thought i´d try and replace the plate resistor for starters and take it from there,that and as i´ve done away with the footswitch jack for the trem install a microswitch to disengage it completely.
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Re: Italian tubers

Postby Racing on Sun Feb 10, 2013 11:36 pm

The ol´ugly Studio 10 came full circle. Things fell in place like a giant jigsaw...

So.

http://www.youtube.com/watch?feature=player_embedded&v=rQaN9s45msY

There ya go. One single end old italian of approx 6watts. Sound is retained kind of over the entire db spectrum.

Axes used are a paulie with OEM Gibby P90s and a mid 80s Washburn prototype with a hotrodded PAF.(DC´s like 9.3k)
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Re: Italian tubers

Postby Racing on Fri Mar 08, 2013 1:16 am

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´N as i´m completely off my rocker i ran into yet another FBT 500-R...which is seing daylight in "Racing edit" come tomorrow with any luck.. :mrgreen:
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