Sound Lead 100

Burns, Selmer, WEM, and more

Sound Lead 100

Postby Racing on Sun Mar 20, 2016 11:21 pm

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Look. This time out i could do with a little help cause...i have NO FRIGGIN IDEA what this is.

The brand "Sound" per se was Italian but...up here in Scandinavia they were imported by Hagstroem and dubbed DNS. DNS för Denmark,Norway,Sweden. This then..i strongly doubt to be an Italian made DNS.

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I bought this thing off of German ebay and it is surely European made. No doubt. At first,just judging by the pics,i thought i had run into an 807 powered amp. Powertubes 807 that is,which in essence is a high voltage version of 6L6 if you wish.

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As it turned out though the joke´s on me i guess.

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Now. This is an amp of ample proportions alright. Goes for the transformers as well.

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Uhu. Seems one of the badges is missing.

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Nah. No 807´s but...EL-51´s! I guess some of you can recall that i recently did a couple of old Swedish made Philips amps that sported EL-50 tubes? Well..

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The powertransformer is absolutely MASSIVE. Like the thing you´d expect in a 200w amp. aaaaaaaaaaaaaaaand yep. Them are dropresistors that are soldered to the side of the OT.
Stacked smoothing caps...tells a bit of the story. Nope. This is no 300V amp. True that.

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Yes. That is a crapload of diodes,no argument. They´re there for a reason though :wink: Summary however is that the build is half neat actually. The manner in which various pts and builds are executed tells the story i guess.

Then a word as far as the various jacks. Never seen the likes. Mains one for instance is REAL puny.
The two switches in turn are for mains and standby.

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The sockets in turn. Up intil this point i had been of the notion that this was an all tube amp. Not so...

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The two novals are ECC-82s..

As it turns out i checked pricing and availability of EL-51´s and...nooooooooooooooo....just noooooooo... So. Googled around a bit and found out that i could replace them with KT-88´s for approx the same power and functions. Ra-a for the OT was about on par as well.

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Sure enough! Silicon! Two channels worth. Now..that kind of clouds it a bit cause..EL-51s hasn´t really been used in commercial amps since the early 50s and..transistors sure wasn´t all the rage at that time.
In short this is sort of a paradox.

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This in turn is the output jack. Never seen the likes. That resistor i presume is the NFB one.

As i fooled around with the amp a bit a few issues became evident right off the bat. Like the wiring between the OT and the powertubes..shot to kingdom come...and so forth.

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The fuse holders are of a variety i´ve never seen before either. Larger then anything out there so for now i simply jumpered some more contemporary stuff in there.
Remember them two drop resistor that were soldered to the OT? Well,they were shot so i replaced them with that golden aluminium cased one in the pic.

Well.
The powertransformer read "500-0-500" so i expected B+ to come in around the 650V mark or so. Sure...fire up time. As i did i soon noticed,did so on my variac,that the voltage spread between the two first hit smoothing caps was skewed. Sure enough..the "equalizer" resistors were shot. Fresh such got installed and at it again..
Curtains. Both of the EL-51´s were damaged,one of them having a busted heater wire.

So. KT-88 time in short.

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´N yeah. KT-88´s installed and ready to go. However..they want way more bias voltage then do the EL-51´s and all i had at hand was approx 50VAC. IOW not enough.

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Now,this is for bench work and trials only. What i did was to setup a voltage doubler. Gonna replace them caps come first thing tomorrow as i pick spares up.
So. Now we had ourselves approx 120VDC heading into a 22k dropresistor and from there to the two trimpots,that are installed in para vs ground. Works like a charm and all said and done i came to hand them 88´s approx minus 75V or so.


In short we´ve got ourselves a working amp again. Not that it sound all that to be honest...but it works. Rather silent in idle too. No matter...it works and that kind of leads up to...what to do with it?

That said though i ask for any and all help as far as what this is cause i have NO friggin idea!

About anything in sight says "Tesla" but..i´ve been around my fair share of former east-block amps and this one´s simply to tidy to the build. (Tesla=former Tjeckoslovakia)
Last edited by Racing on Sun Jul 10, 2016 7:59 pm, edited 1 time in total.
Racing
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Re: Sound Lead 100

Postby Racing on Fri Mar 25, 2016 11:52 am

Still paging anyone out there with more info.
For the sake of argument,this there is the mains jack.

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Obviously a 3 prong one. Here next to a common sized BIC lighter,which hands perspective i guess.

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Close up of its markings.



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The rear facia. As stated the stock fuseholders lacked their insert as well as actual fuses. The standard used left gaping holes in the facia and there was no replacements that would fit the bill.
Solution was to weld washers to the chassis inside to make the whole thing work,and i´d say it all worked like a charm.
Breakers were taken apart and cleaned out as well while at it.

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A regular IEC jack was installed. Fasteners replaced and so forth...

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Speaker out was replaced as well,with a regular 1/4" tele. No marbles for that one..

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The PSU part of the amp was cleaned up quite a bit. The bias board was setup in a more correct manner. Main grounding point moved.
For some reason the amp lacked any and all smoothing of the voltage heading for g2. OTOH the actual drop vs g2 was minimal in stock form,which it certainly isn´t now.
The KT-88´s asks for a maximum of 600VDC vs g2 and...yep. Zener diode time. With the added capacitance for g2 B+ jumped a bit chiming all in att just a tad over 700 volts.

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Tagstrip vs the powertubes was replaced as you can see and components added to handle the tasks at hand.

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Sort of hardwired and tagboard installed at the same time. Idea,of course,is for a sturdy setup. One that´ll handle to be tossed around.

So. Right there and then we´ve got us a running powerstage,sort of. Lacks the phaseinverter and..speaking of which the idea of mine here is to set a longtailed pair up based on an ECC-83 and then let that head into a triode each of an ECC-82,which will be AC coupled and set up as cathode followers. Main reasoning behind that being that i want the 88´s to be handed the swing the ask for but atop that ample current for them to improve transient response.

Seing that the amp will in short get a separate preamp chassis due result.
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Re: Sound Lead 100

Postby Racing on Wed Apr 06, 2016 10:24 am

For various reasons activity has been a bit on the low side lately but...

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Time to make the call as far as PI. After talking it over with Aleks i opted to run a regular longtailed pair heading into a pair of cathode followers. For obvious reasons i guess.

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After tossing the idea back n forth i opted to run with the stock solder strips. Mainly for space reasons. See,the chassis is rather shallow..
Stock they were set heightwise by shimmin with a pair of regular nuts..not exactly my idea of a pro install so proper stands were located.

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The cab in turn got a good cleaning. First up with windex and a nailbrush followed by a steam clean. As a carrying handle was missing one was installed.

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The caps got a minor dab of glue each to stay in place. The resistors tho were just installed as is. Distances and weights involved are so short/low so it´ll work as is.

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To get an idea of how the KT-88´s and the new phaseinverter setup worked i flicked the switch and let her rip. Yeeeep...that there is a PPIMV pot wired in there as hip-hap as they come to be able to check how it sounded at WOT without going deaf.
Summary was...yeah. We need an all tube preamp. :mrgreen:

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Mockup assy time. That there piece of sheetmetal bolted to the preamp chassis is the stock shield for the silicon preamp. Not to be handed a new task in life,to become a chassis for the novals needed.

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Anyone in need of a "barely used on sundays" silicon preamp? :mrgreen:

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This time the caps involved got installed ontop for space reasons.

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Board was cut down and noval sockets got installed. As always the board was put together flying lead.

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Uhu. V1 is rubber suspended. Correct,and as you might have gathered that means an EF-86. Seing the proximity to the OT and powertubes the shields were intentionally picked to be the steel variety.
All the wiring has been run on the outside of the chassis to prevent ills as best as possible.

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Chassis is cramped for space alright. Just check the clearence between the input jacks and the tube sockets.

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Here from a different angle. Yes,the wiring loom within is kept in place by small dabs of non hardening glue.

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Right. Knobs are off an old Winston amp. Thought it could be a cool addition with them oversized ones.

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´N as usual...law n order.

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The grille was treated to some fresh fabric.

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Then for the dual PPIMV control. Not all that much to add really apart from the mere fact that i can not for the life of me understand why not every "old school" tuber in existence sports this. It is THAT usable.

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..and as always it´s all in the details. Might be that the knobs are 40yrs old..they got treated to a good clean and some fresh highlighting.

So.
What we´ve got here is a REAL loud old tuber. One that from a practical POW could be said to losely be based on the Marshall 2203 concept,just that the "high" jack engages an EF-86 instead of a regular extra triode to shove the entire thing into orbit.
Used it for rehearsal the other night and..what can i say? It works and it works as intended and works well.
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Re: Sound Lead 100

Postby Harvey58 on Sun May 29, 2016 5:37 pm

Hey man, i bet its some of the Czechoslovakian home made amps. Its not a factory build or mass production, it would a boutique amp (one piece).
We had many DIY builders in the communism era, we cant buy nothing here, so we must build it by ourselfs from a scrap :D

And here was some good builders, they made mainly copies of Marshall, which plays better than Marshall, really.
But this builders can not afford advertising or so, theyre amps looks visually worse than original (there were no amp parts suppliers etc.) so the amps are less known in the rest of the world.

Of the photos - most of parts and also the tubes, were made by Tesla Czechoslovakia,
also the chequerboard grill cloth were taken from the original Tesla HIFI box.
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The trannys are made of parts, which i also know from the Tesla factory made transformers.

Rest of the amp? Maybe it was somenting else before (radio or hifi amp) and was converted to the guitar amp. Who knows?

Regards from Czechia (now). :)
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Re: Sound Lead 100

Postby Racing on Sun May 29, 2016 11:44 pm

Thank you SO much for voicing up!

Yes. I agree. The amp was most likely made in former Checkoslovakia. By whom i guess we will never know.

Thing here is that my mentor happens to stem from Poland,which at the time was just as behind the iron curtain as was Checko and we´ve talked it over too..and have come to the same conclusion.

Having worked on the amp as much as i have i strongly doubt this being a "hobby project" though. The amp is simply of to high a build quality for that. Well thought through by someone that knew what he was doing.

My take on the matter,to make it all tube,i believe is as much with the original plan and idea as they come too. What i´m saying is that times change,and we follow. Back in the day hybrids became even rather common and everyone and his grandmother placed great faith in transistors. Since we,as musicians as a whole,have learned differently and tubes made for one hell of a comeback.
Ergo..i at least think it stands to reason that what i´ve done is simply a different route/take on the original idea. More in line with contemporary thinking,but using old ways.

Amp is still with me but as it turns out it might be heading for Italy soon :cheers: . That´d sort of,within realms at least,make it come full circle i guess.
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Re: Sound Lead 100

Postby mozz on Mon May 30, 2016 12:48 am

I love the specs on the EL-51's. Too bad that were not just a old tube nobody wanted to use.
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Re: Sound Lead 100

Postby Racing on Mon May 30, 2016 10:42 am

Agreed.
Them some BAD mf´s right there.
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