Schaller KV-50

Burns, Selmer, WEM, and more

Schaller KV-50

Postby Racing on Fri Jun 20, 2014 1:30 pm

As some of you might have noticed i commented in the Schaller thread in "off topic.
To no avail though it seems. None the less.. Some of you are familiar with my fablesse for the odd and peculiar on occasion,and since a while back i´ve had my eye open for one of the bigger Schaller combos.
The same combos were also marketed under Hofner badge,but were as far as i know all built by Schaller.

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Amount of info online on these old warpigs is limited to say the least. This particular one in turn is DOA...so to be honest i have no idea what to expect.
The KV-50 were at first manufactured as all tube,which the amp in question is,and from 1967 on as hybrids with a transistorised front end.
That..iow place this amp as far as vintage,at least to a limited degree as the model was introduced in late -65 to my knowledge. Before that these units were dubbed KV-40.

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Anyways. Rather "AC-30ish" to the looks as can be seen. In this particular version it weighs in,according to radiomuseum,at 33.5kg. IOW not the lightest of combos,mind you..out of those 33kg approx 7kg is the reverb!
Reverb?
Yes. The reverb of these units are built around a magnetic disc,much like the old Italian Binson echos.

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The perforated box hanging down from the preamp box,the amp is built around a separate preamp and powerstage chassis,is the reverb unit.

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(Pic stolen via i-net)
Looks like this according to legend. These reverb units are anything but simple to the build,however after restoring a few Binson units..i´ll at least have a go at it to see what drops out of the bag.

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These amp were relatively expensive new. Schallers more heavy duty "bune"(stage) amps were no misfits. As far as i´ve read though they were clean amps,and period.
Reverb. Indeed,that and a tremolo. Just like various other german amp makers the Schallers use a photo resistor for tremolo work.

From what i´ve gathered these early KV-50 units are from a tech POW about deadringers with the earlier KV-40 units.

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One of the things that made me jump the gun with this one is that it´s still all intact. All the knobs,hardware asf is there. IOW..no running around the worlds various e-bays and what have you not for spares from that respect.

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I believe the word is...unrestored :mrgreen:

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Ah. The hotroder in me (i build race stuff for a living remember) kind of thrives on surface rust :twisted: . That aside,them brackets there... again..rather AC-30ish.
Point being that these amps could be had with a chromed "cradle"/swing. Just like the 30´s. An AC-30 though it is not. The twin EL-34´s alone attest to that.

Judging from the schematic for the KV-40 and later transistorised KV-50´s these amps use an ECF-83 for PI. To be blunt,as this is to become a hotrod,using "mixer" tubes in the PI position...nah. Previous experiences on my behalf trying to get them to sound "right" is just more work than needed...
First up is to get this old thing going though. As is,and i expect the reverb to make for a rather massive feature as far as work involved.

As i know that some members have brought Shaller amps up before,please voice up if you still own one. As far as this unit i´ll be sure to post pics of progress as the amp comes around.
Racing
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Re: Schaller KV-50

Postby Racing on Fri Jun 27, 2014 7:05 am

Oh.. :o


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One slightly battle scarred Schaller KV-50 showed up. True enough one of the older all tube ones. Full of dirt and old webs and with the wording "DOA" (dead on arrival). At fist i was a little doubtful as to if it all was there,but...unfounded. The amp was indeed complete.

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The speakers,whatever they are. Goodmans they´re not though.. None the less datestamped 06/-66 and thereby i believe we´ve dated this old Schaller for vintage. In turn,from -67 onwards they´re hybrids- with a transistorized front end and in turn reverb unit.

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Picked the thing apart first thing i did,and indeed...that "tank" hanging from the preamp chassis is the reverb unit. As it showed..complete down to the last nut.

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The PSU/powerstage unit was a mish-mash to say the least. As you can see...three sockets all in all. Twin EL-34´s and one ECF-83. There´s a sort of "housing" that you bolt down to the chassis to protect the tubes when installed. One of the main e-lytes has been replaced obviously.
In turn..that some seriously dimensioned trafos!

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The one side of the powerstage chassis sports yet another two octal sockets. These are indeed sockets,and run the various voltages back n forth for the preamp section. One for mains and standby and the other for the various voltages needed for the preamp and signal return for the powerstage.

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The other side of the chassis sports this old DIN jack for external speaker. Of course it´s going to be replaced with a common tele ditto. The amp uses two 16 Ohm speakers in paralell stock btw. IOW for a total of 8 Ohm.

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That there wasn´t as pleasing to the eye though. At first i thought it was residue from a blown e-lyte,but it´s not. It´s rust inhibitor. To what avail..? You tell me.
However..some Mr Handyman has been at it previously as can be seen. NOT for the better.

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Apart from a few replaced high power resistors the rest of it is stock as far as i can see. I need to reevaluate this a bit though.. See,the KV-40 is quoted at approx 400VDC B+. Doing the math for the KV-50 should make it end up at approx 450-460VDC. However..this one lacks any and all voltage selector rendering ONE primary only and that puts B+ at a rather severe 500VDC sharp under load.
That is running the jagged edge for the first main e-lytes...NOOOOOOT all that happy ´bout that. In turn it ALSO leaves us with a situation where screen voltage needs to be handled.
As you can see from the schematics there´s basically only a screen resistor running for each tube. No choke,no drop resistor.
Giving thought to a pair of zeners in this case. Need to control voltage for the screens in a WAY better manner seing that we´re at the design limit for the screens as far as voltage and 500VDC approx. NOT a good thing.
Ergo,for evaluation i´ve replaced the EL-34´s in there with a pair of metal base Mullards,just to be on the safe side for now.

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Then for Mr Handyman. Obviously Mr Handyman has reflected over the rather high B+. His solution was to install a 680 Ohm dropresistor heading for the PI and what have you not,and in turn one 10w resistor heading for ground to "burn off" voltage by loading the PT down. Well guess what.. :mrgreen: . You COULD say that resistor has been blown to kingdom come...
In short..i need to adress this. In turn he´s replaced the screen resistors with 150 Ohmers. Should be 100 Ohms stock.

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Yep. 150 Ohms. But see...that´s nowhere NEAR a solution or remedy for the situation at hand.

Well.
That aside i looked the whole thing over and..fired her up. Sound came out alright,albeit very low key and very distorted. Checked and reflowed a number of vital solderjoints however,and....presto. We had ourselves one working Schaller KV-50. :mrgreen:
Albeit as noted with REALLY elevated voltages. Now...i´m to replace anything electrolytic within sight anyways,but OH are we ever running the edge (and past) at this stage as most of them smaller quoted 8uF ones are rated at 385VDC. In short...boom risk. :twisted:
None the less..the amp works.

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Then for...the electromechanical porno. Yep. Intact. :shock:
One EL-84 as driver..

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...and then yet 3pcs of ECC-83 for taking care of signal at the other end of the reverb chassis.

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´N yep. All there. Oscillator,photo resistor-the works. Mr Handyman had been at it though,again. Them what i PRESUME are to be x2 caps upper left was shot,cracked. In turn there´s supposed to be a 2uF motorcap..which has been replaced obviously. No matter,i replaced the shot x2 ones with a couple of worn spares just to get the whole thing going..

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So. Motor,idler wheel and magnetic wheel. Turned out that the idler pulley (which in reality is a gearing) had seized completely. Took care of that with some good old fashioned violence.. :mrgreen: . Even the two rubber bands for drive were still serviceable! In short,we had ourselves one as far as i know at this writing,working reverb unit.
Still haven´t checked the actual reverb FUNCTION of it though. But the motor and mechanics of it works and the tubes at least all fire.

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´N here we go. The whole enchillada. Doesn´t look all that complex does it? But rest assured..it is.

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´N it is all run and controlled from here. The preamp section. Sort of built "Hohner style",just more tidy and more logical.

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A few solderjoints were ruptured,which was easy enough to pinpoint and as stated above..we had ourselves one working Schaller KV-50 after a little while.
Doesn´t sound worth a crap yet IMO but given a few more hrs today of TLC we´ll see where it all ends up.
Checked the tremolo,which is optical too,and that works like clockwork.

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A few components have been replaced down the line as is evident.

What up first is the replacement of e-lytes in general. If i´m to make this SOB survive the voltages,the rather increased such,needs to be take into account. Ergo replacement e-lytes will need to be of 450VDC at least and in turn i´m going to up the capacitance of them too.
All tubes are Tungsram btw.

Amp was even delivered with the OEM casters. Ie;the wheels for it. Size wise this is about on par with an AC-30,and that goes for approx weight too. In short..half heavy 212 combo

Well. That much for initial work and reflections. Will take it from there and update as we go along. Giving thought to making a short video of it in stock form,if nothing else for reference as i presume not all out there are familiar with a stock Schaller combo.
Racing
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Re: Schaller KV-50

Postby peter horvath on Fri Jun 27, 2014 3:25 pm

Looking good!

As a side note, you are making me lust for more obscure amps now. :twisted:
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Re: Schaller KV-50

Postby Unit_1 on Fri Jun 27, 2014 7:28 pm

fantastic finds, some future restored amp lovers will thank you for your work!
and if dirt were dollars you'd be king! :highfive:
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Re: Schaller KV-50

Postby Racing on Sat Jun 28, 2014 9:00 am

Thanx boys :D

Pushed forward a bit yesterday.
Got to replace basically any and all electrolytes. Point being that i upped capacitance slightly for the ones further in the amp and at the same time upped voltage capacity.
Why?
Well,the schem i got is one for the KV-40 and for some funky looking later KV-50,the one with a transistorized front end. Issue at hand is twofold.
This KV-50 sports a PT that will make B+ end up approx 100VDC above what´s reffed in the schem for both above. I´ve however found ONE handmodified schem online that states about the same thing as i see on my DMM,and hence..

500VDC in turn makes for a situation where voltage needs to be looked into as far as screen ditto. So. Ripped them megahuffalarge ceramics of 150 Ohms out of there and replaced that with a way more mundane sized 100 Ohmer per socket AND a 27V zener each.
That..took care of any and all ills as far as that goes i suppose cause now screen voltage indeed is beneath them fabled 500.. (B+ ended up at 510VDC under load).

However it also plays havoc with the referenced voltages further in the amp. Mr Handyman had installed yet a pair of them megahuffalarge resistors as first drop. A pair of 680 Ohm ones in series,for some reason.
Schem states for 3k here...and as voltages are up as much as they are..i opted to install a 10k one that after a little calculus ended up at 5w. Haven´t gotten around to check actual voltage after that stunt yet,but..amp at least works now.

So. Flicked the switch and lo n behold. Amp came to life. Had intermittent function of the tremolo and that was traced to a bad solderjoint. Simple enough.
Took to replacing the wiring for the speakers (again Mr Handyman) and hooked the whole thing together. Hm. Could have been worse. No argument.
However the sound omitted is nothing i´d write home about. Clean..to a certain level,then distorted and as the distortion comes from the pentode side of the ECF-83 it trule leaves something to be desired. :Zap:

Be that as it may.
Reverb time.

The motorside of it had been modified earlier. The motorcap in the schem had been replaced by some funky "i´ll trick it up" setup by Mr Handyman. I presume fresh motorcaps are simply to expensive.. :nutjob:
Anyways. Picked a fresh one up,together with a pair of x2 caps if needed. To no avail. Motor will start if you "help it",but not on its own. Further,interference can clearly be heard as you wiggle the wiringsheath around,so i suspect one of the wires within the sheath is broken.

That said. Fooled around a bit with the trimresistor for the EL-84 to make voltages end up more on par with the schem..and let her rip. Nothing.
Started to trace the signal with the scope and it dies out completely as it enters the oscillator circuitry. That is how far i got last night..

Good news is that the reverb is all complete at least. As such,,it can only be a matter of work to get it going again,and maybe a spare or two.

So.
Amp up and running. Sound out of it is..ok. Not more than that though. Stock speakers are on the bright side IMO but that can be handled by trimming the onboard James networks. In turn the amp for some reason sports a presence SWITCH and engaging that makes the amp to bright,to shrill.
I suspect the amp to be able to use the stock speakers when we´re going to start pushing the envelope a bit though. They don´t sound half bad really,just on the bright side a bit.
Goodmans (which these amps could be had with) they are not however...and i have no idea what they are.? They´re marked "FEHO" Made in Germany,and that´s it.

Well. Project will be on hold for the next couple of days. Social duty is calling...but...
..to be continued..
Racing
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Re: Schaller KV-50

Postby Racing on Wed Jul 02, 2014 12:55 am

...and so the saga continues.

First up i souped the preamp per se up a bit. See,to make these units pure cleanmachines (i suppose?) the entry stages are all run very very conservative. In fact to a point where the actual topology setup entails a "tail resistor" for each triode. One effective way to keep gain down i suppose.
Anyway. I did away with those and dropped the inbound signal caps and set the entire enchillada up to me more guitar oriented. What came out the other end was an amp that actually could be run from clean and into a half nice distortion :shock:

Mind you,this is a mastervolume equipped amp. The point here being that the phaseinverter is an ECF-83 and my previous experiences with them "mixertubes" where one side is a small signal pentode and the other a triode is so-so at best TBH.
Thing here is that thus far i´ve played around with ECF-80´s and ECF-82 as well as PCF-82´s and my summary has been that they are a true BITCH to get to sound "right" at all levels.
Enter this ECF-83 and..in contrast to the above it´s not half bad really! To be candid though the tone out of the amp as volume goes up gets rather stiff and hard,which is to be expected i guess.
In short i´m going to dwell on this ECF-83 a little further before passing final judgement.

Amp has a really nice coarseness to it as of current. That minor mod made for quite a difference,and i´m still rather undecided on what to do with it. Time will tell.

The reverb then.
I´ve run around like a one legged chicken for a No of hrs. To no avail. I´ve hit everything in sight with one of my scopes and STILL didn´t get it.
Like...
Plate of the EL-84 driver had like 260-ish VDC in idle right. K...a few seconds later it had 5,5VDC..to return to the former value.
To..putting out as good as signal as could be expected vs the heads...to get nothing in return...to...a few moments later getting like 17VAC in return for the preamp.
WTF?
It had me stonewalled for a number of hrs let me tell you. ´Till it dawned upon me. The wiring bundle. The bundle that connects the reverb chassis and preamp one. Wires are after all approx 50yrs old and end in a mere noval socket and...damn that thing looked like a friggin trainwreck within!
So. Tomorrow i´ll be replacing some wires that much is for sure. TBH i´d be real happy to replace the socket with somethng more in tune as well.

So. The reverb motor. The Papst AC motor.
Mailed Papst and they were REAL helpful. Sent me the complete specs for the motor,but it surely is out of production. Hm. Both Papst Germany and Sweden was on the case....to no avail.
Well guess what. There´s this thing called ebay.. :mrgreen: ,and it turns out that the EXACT motor can be had via US ebay! A 220VAC motor..on US turf? WTF?
Well.
Thought i´d drop a call or two to various vendors around the country come tomorrow but if that falls through...US ebay here i come.
Racing
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Re: Schaller KV-50

Postby Racing on Fri Jul 04, 2014 9:37 am

Have pushed forwards.
Replaced the wiring between the reverbtank and the preamp chassis. All for the better,and revived the actual socket at the preamp chassis end.

In turn i took the various mechanical parts of the reverb apart. The idler wheel wasn´t turning as smooth as it should IMO,and this was due to the old grease in there simply having turned to mush.
A gunbrush and alcohol took care of that. Repeated for the magnetic wheel axle and bearings,and as a whole the entire thing now rotated as easy as ever.
Ordered one of them Papst motors from the US. Expect it to show up here sometime next week. Sorted the oscillator circuit out,and as a whole we´re in business as far as that goes.
Worse then with the tapeheads.

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Me n Aleks took the "bighuffamachine extraordinare" to it,and the simple truth is that they´re all shot. Should show SOME sort of reading as far as inductance,and they don´t. Atop that we were getting capacitances along 100pF or so,which in essence tells us that the heads in Q are broken.
Sux,but that´s how it is. Now...Aleks knows WAY more as far as these things go than me and according to Aleks it is well worth a shot with basically any tapeheads out there,playback ones,as long as i can fix them to the structure. Well...building racecars and engines for a living can come in handy at times,so..right now i´m looking for some reasonably priced heads to install.
That aside i gave the entire reverb a once over and cleaned the solderjoints asf up,replaced some of the groundbus wiring asf.

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That done i returned to the actual amp per se. The cab got a second hit of windex and a nailbrush,and for the really hard parts/spots i used cleaning acetone on a rag. Mind you,when using acetone on tolex..judgement is adviced. It is NOT a cleaning method for the faint of heart,but it sure works!
As you can see yourself the cab is somewhat of blue-ish purple-ish. Rather nice colour IMO!

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Then for the tip of the day. It is rather common that the controlknobs of old amps are fixed by the means of grubscrews. Time and abuse doing it´s fair share often end up in the controlknobs being like welded on,and them small grubscrew don´t play along worth a damn.
So.
In this case it was rather easy to handle as the controlknobs are all metal,nickle plated brass,so what you do is attack them with a good old fashioned heat gun AND rustpenentrant AND some force by a screwdriver that FITS and gentle blows from a hammer.
The hot controlknob can be a handful,so use a pair of pliers to keep them steady as you try and turn the screw. Again judgement is called for,and if the screw still won´t budge..more heat.
If the controlknobs are out of plastic this becomes a sort of walking the jagged edge,but always rather add more heat than force.

That done i fooled around a bit playing the amp,just this time i put a MXR overdrive infront of it and..nah...just nah. The stock speakers seems full of oxides and thus i get a rather ugly "fuzztone" atop it all. Dunno what to do about that as of yet. If i can "play it clean" or not. Well,only thing not picked apart thus far is the baffle,and that needs to come out for a clean and rinse anyways so...modding to cater to modern day n era speakers is a breeze..

That said. I´m also done with the ECF-83 for PI. Simple as that. I opted to replace the master control with a 500k one,100k stock,and the mere truth is -again- that the pentode side of them "mixertubes" simply do not take kindly to overdrive. It sounds bloody awful in short.
That atop i´m going to install a PPIMV anyways to take full advantage of the amp,and as such...well what to settle for is anybodys guess i presume.
Giving thought to a paraphase. Like their rather "jagged" behaviour..
Racing
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Re: Schaller KV-50

Postby Pitchfork on Fri Jul 04, 2014 4:43 pm

Tape heads- try John Beer at Ampfix in Devon. He may have stock of heads suitable for Copicats available
http://www.amp-fix.com/
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Re: Schaller KV-50

Postby Racing on Sat Jul 05, 2014 1:52 pm

Thanx.
Wrote the very polite John at JRF the other day and we´re going to attempt sorting this out.

For now at least...this amp as stated does NOT conform entirely to the schem. Voltages as noted are approx 100VDC up and in turn for instance the reverb motor is a 220VAC one-instead of the 130VAC one in the schem.
Motor was shot too,and by pure fluke i found one for peanut money on US ebay,so that´s bought and paid for. Ditto i managed to scavenge a set of generic tapeheads for old MIJ crop mid -80s taperecorders,so i´m at least going to try them out for size. If it works...then all good i guess.

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Well. As i´ve written before the amp has seen an internal fire at some point and some Mr Handyman had butchered what needed to be and basically pulled an as minimalized effort as poss.
´Nuff a that..so i opted to clean the powerstage/PSU chassis out as best as i could,and replaced a lot of the wiring in the process. For some reason this amp lacks any and all fuses entirely,and that is something i will modify to fit. Running a toober sans fuses is just pure friggin folly. One´s already been installed as you can see,and that is for the B+ line.
Ditto for the OEM mains wire. A three prong alright,just that safety ground wasn´t connected. I presume,again,the works of Mr Handyman.
So.
One main B+ fuse. One mains fuse primary. One each for the two heater circuits and god knows if it wouldn´t be a great idea to add another one for the cathodes of the powertubes too. Easy enough all said n done.

These amps are indeed built a little different. The B+ line is more set as "taps" then the usual step ladder. Ie; some of the voltages are really let to soar,and IMO that leaves you with a clean amp most of the time alright,but also a rather harsh and shrill tone.
So. reset that. If need be easy enough to convert back and that made for instance railvoltage for the PI drop lika almost 60VDC. (ended up at 380VDC). Rest of the amp followed suit as far as voltages.
In turn i abandoned the stock ECF-83 for PI and remodeled that a few times-just playing around with it. Tried a common LTP...then a paraphase and in turn a floating para. Ended up settling for the latter.

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As such this thing got a PPIMV pot too. I can not stress enough in how high a regard i hold the "common" PPIMV for highpower amps. Now that said,please have in mind that most of these German made amps are REAL loud as transformers asf are purpose built more often than not. Ie; NOT generic stuff just picked from the shelf.
With the PI reset and the PPIMV in place the tone out of the amp started to come together. Difference like night and day.

These amps are,fwiw,real silent in idle. They conform to "the golden rule" in as much that the first hit e-lyte is grounded in the exact point where the negative from the bridge hits the chassis. While at it i at least replaced the 50uF+50uF e-lyte,and i´ll be damned if the thing didn´t turn more silent yet in idle :shock:

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Now. As much as i know that some frown on the practice i had to handle the rather elevated voltages vs the screens of the powertubes. Since a while back my mentor,Aleks Niemand,taught me to implement zeners when in doubt.
From a practical standpoint what they´ll hand you is a way more agressive and rapid powerstage. Kind of "4 doors,no waiting",and it really works and works well.
The massively oversized 100 Ohm ceramics is just cause i had them laying around,but anyways..they´re mainly there to combat RFI and EMI.

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Ah. The nickel plated controlknobs. Got them off using a little heat from a heatgun,liberal doses of penetrant and a screwdriver that friggin FITS. Hit them with the buffer and some polishing compound...and then handed each one a fresh dab of orange at the dot.

So?
Where are we at right now?
Well,the electric part of the reverb is up and running. Oscillator is doing what it´s supposed to and the recovery stages are all up and running too.
I deleted the tailresistors for the preamp stages and that made amplification jump to a degre where half decent distortion can be had already as is. Of course this also due to the reset phaseinverter and PPIMV pot.
Trem is up and running as it was going out of style. Cab has been cleaned out aso aso aso.

The stock FEHO speakers though.. I´m undecided. From what i´ve gathered these amps could be had from Schaller with either german made FEHO speakers OR with british made Goodmans.
Over the years i have to say that the ONLY german brand speaker that i deem usable for modern day n era rocknroll work are the Isophon ones. The old AlNiCo P30/37 are IMO sort of a hidden secret of the trade.
These FEHO´s..are not. Or...i´ll put it this way,they are WAY WAY WAY better than any Elbau or Bauer or whatever.. Up to Isophon levels though..they´re not.
The point here being that as distortion is introduced and in turn increased the FEHO´s simply turn to bright. They create a rather ugly fuzz tone atop what the amp brings to the table,and...no. Just,nope.
i´ll replace them,dunno with what as of yet though.
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Re: Schaller KV-50

Postby Racing on Sat Jul 12, 2014 10:56 am

Two steps forward,one step back.

Got to tinker a little more with the amp itself. I remodeled the bass channel to become the channel that works sort of like the stock one. This by installing a tailresistor to the entry triode once again,and that tailresistor for trial use then as a trimpot.
In turn i installed a small e-lyte of 4,7uF across the second stage cathode resistor,and then started adjusting to get a basically all clean channel. Almost at least,you can get a very minor crunch out of it at wide open throttle but that´s it.

Then. The microphone channel. Stock this channel is wired a little different. In essence it only uses the second stage for direct amplification,but to avoid phase cancelling the entry stage is at least there and involved as much as phaseshift.

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Well,out the door with that and an EF-86 was put into that position instead. One EF-86 is still just one phaseshift so that signal is now routed towards the bass channels second gainstage,and hence...we´re in business. :mrgreen:
Outcome?
It was indeed everything the doc could hope for! Now this amp sports one wilder 83 channel and one just about squeeky clean...and in turn atop that a VERY usable EF-86 one. :mrgreen:

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The reverb then. In essence i was flying blind. The schematic was not correct,and i had no idea what so ever what Mr Handyman had been up to and i had no REAL idea what Schaller had in mind.
But.
I installed fresh tapeheads right. Tinkered along,and then yesterday me and a close friend was at it.... Amp up and running and i turned/speeded the drum up by hand and got....static :D :D
In short the playback side of the system was working! One could clearly hear how static was amplified and this could indeed be controlled by the reverb pot for amount. That brought forward that the FeOx of the drum IS ok. Heureka!!
But.
Still no cigar as far as getting the bias to reach the drum,nor the signal.
Hm

I was at a point where i started having issues as far as how to approach this.
Now,i was certain that i was by no chance alone on the friggin planet playing with this kind of reverb,and had searched the net for others already the day before. Wrote a few gentlemen a short e-mail,and guess what.... :twisted:

I got a reply from a Mr Detlef Rieky in Germany,and...bingo! See,Mr Rieky had already gone though great lengths approaching this "the german way". Ie;he had done a complete reverse engineer of the amp before overhauling his and ergo...
I now have a complete schematic for the amp!! YES!! I´ve got a CORRECT schematic for the actual amp!!! Indeed...it shows that Mr Handyman has been at it.

Now,that´s not the same as stating that the reverb will work,but at least it hands me a fighting chance.

...to be continued..
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Re: Schaller KV-50

Postby Racing on Sun Jul 13, 2014 11:19 pm

Pushed forward a little again.

First up i modded the EF-86 a little to hand me a bit more bottom end. Of course it made that channel more aggressive as a whole when asked to be. For the better.

Then i took to redoing the reverb topology per the schematics i got handed. Still no dice,but i believe i´m onto something. Turns out that i´ve got an oscillation of approx 35kHz or so from the EL-84 which i presume is all good,however...
I get something similar from the tube setup that is supposed to push signal from the preamp,and signal ONLY. There´s a feedback loop,which there of course needs to be,but the thing is that within that loop i´ve got a triode that oscillates at approx the same frequenzy as the EL-84. Now that CAN`T be good!
So. Going to take a closer look at that asap.
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Re: Schaller KV-50

Postby Racing on Thu Jul 24, 2014 9:06 am

Image

The new motor,the old one was shot,showed up from the US and all is good as far as that goes. However....

Gentlemen. I need your help.

Image

By now i´ve played around with various tapeheads ´til kingdom come,to no avail. I´ve brushed up on induced magnetics in every form there is. From Lenz to Faraday,and i´m still at square one.
I´ve tried to use a different,previously unused,part of the drum. I´ve played around with a minor dozen of solutions as far as tapeheads and i´m going nowhere.

Thus i´ve been told that this comes down to the specifications of the Bogen UK-100 heads and ...that it is quite common for these heads to go O/C.
Ergo,i need your help in finding working ones.
From what i´m told these heads work "different" in as much that they sport a different inductance as well as other properties. ONE of the issues i´ve got is that i have no idea what so ever what either that inductance is or what "other properties" brings.?

What i know for sure is that i can´t record. The playbacks works as intended though.

If this gets any worse i´m giving thought to remodeling the unit to become a tape unit instead. That way i can still use the features of the amp/reverb and hopefully get it to work as god intended.

However. First thing´s first and my first plan of attack here is to see if it is at all possible to scavenge usable heads anywhere in the world. So..if you happen to know of any Bogen UK-100 heads PLEASE hollar!

As far as the actual amp per se goes though i´d state that it´s done. Works just the way i want it to.
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Re: Schaller KV-50

Postby Pitchfork on Thu Jul 24, 2014 5:42 pm

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Re: Schaller KV-50

Postby Racing on Sat Aug 02, 2014 10:01 am

Thanx.
Thus far net result has been zero. As you might be aware i´m no stranger to the odd amps and one normally get hooked up with whatever within reasonable time.
Not so this time out though. I have a hard time relating to why them heads are about unobtanium? There HAS to be old surplus around. That ALL Bogen UK-100´s in the world has been used up is just silly as a proposition as far as i´m concerned.

It´s come to the point where i´m seriously considering redoing the thing into a regular tape echo. As i work with metals,lathes,bridgeports and AC welders on a daily basis it wouldn´t be the end of the world,however pulling that mod off would mean there´s no turning back.
All functions of the unit would be retained though.
I´ve even considered buying yet another one,that at least sports A fresh head,just to be able to measure what´s needed as far as inductance asf. Pretty steep parts bin in such a scenario as the old Shaller 40´s and 50´s ain´t exactly cheap.

Amp in itself is up and running like you´d never believe though.

In fact....Image

...to the point where it was one of the main guitar amps past saturday,and it handled that with flying colours.
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Re: Schaller KV-50

Postby Racing on Sun Aug 10, 2014 12:03 pm

I´ve about exhausted every option there is as far as them Bogen UK-100 heads. Or at least,it feels that way. Looked worldwide to no avail.

So. That leaves me with the option to "redo" this into a tapeecho instead. In short just settle for how the whole thing is supposed to look and work and get to it i guess.
As i own a lathe and bridgeport it´s not the end of the world making such a setup. However..it simply feels like sort of a defeat. Not all that much to do though,and making it into a tapeecho instead at least leaves all the stock functions intact. Ie; both reverb and delay.
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