Luxor KW 12

[Racing]

AGAIN a Swedish made old tube PA amp. As it turns out a rather large one. Thing is the size of a small friggen table! Didn´t expect that seing the mere twin 6V6´s!



Got it complete with the old Philips branded microphone even! Which...turned out to work!



Presume this one to be an earlier jobbie too. Still tho...output impedances we use to this day. For the better.



Those of you that have followed my ramblings i guess by now know the size of that "new" workbench of mine. No..no,this is NOT a physically small amp. No Sir..
Nor does the word beautiful come to mind. Not exactly heading for the museum of modern arts is it?



Hooooooooooooooowever.. Now we know why the mere size of this thing is what it is right. That´s a bottle or two alright. Lots of iron to boot.

So. This amp works the "old fashioned" way by the means of a hefty sized choke taking the first hit. Yep,60H worth.. the PT in turn i guess is a given and the other side of that MASSIVE choke we´ve got the output transformer and at the far left end ...again an interstage transformer that acts as phaseinverter. Hm.
Different setup to say the least.



Yep. So that little buddy right there is our phaseinverter.



Uhu. Albeit one Philips and one RCA they at least digested reasonably similar amounts of current in idle. However..once on the U-Tracer of mine..numbers don´t lie,these were done with. IOW time for replacements.



Yeah. Seing the innards of this thing i´d state it is either really really late -40´s or early -50´s. Anything capacitor was replaced right off the bat to be able to check if the thing was alive. At all. Sure enough,works it does.



No. Your eyes ain´t fooling you. That there is a second choke,one of a mere few Henrys.

That done... B+ was all in at 330VDC approx and i presume that number will jump big time as i clean the thing up. The 5Y3 rectifier in turn..no saying what condition that´s in. No matter really as i want to maximize voltage best as i can i´ll replace that with a 5V4 due time.
..and it does sound alright. Tone control is via a 6 way switch for whatever reason and..that switch does its job i guess. Am i saying you could use this thing for guitar right off? Yeah,i guess. If you hook it up via the "mic" input. Hooked to the "gram" input..not so much. Turned weak,sans any and all balls and rather clean only.

This one needs a fresh chassis as well as cab. Cab...woods all the way. Reason is simple,the stock chassis is simply to much "Lego" to me. In turn i want to adress personal safety,meaning that loads needs to be done as far as the transformers and what not.
I presume DC voltage will chime the bell around the 380-400 volt DC mark all said and done and..nah. Need to make the thing safe to handle.

[Racing]

Had yet another one of them "pre used" Marshall clone chassis out of aluminium standing around. Way more appropriate seing the power and what not..
A fair amount of work has already been put in as far as making the thing WAY more safe to handle once done and ready to rock. Wiring and so forth..



Yup. Moved the voltage selector to reside within the chassis. However that "top hat" thingy there protrudes a tad to much i think so..i´m going to try installing that octal socket that is the voltage selector to the inside of the chassis instead,and then on stands.



Uhu. Mains transformer. WAY more safe to handle. Rectifier in turn is a brand new Sylvania 5V4. Hope that´ll hand me what i need. That small choke i mention further up turned all in at 6H. We can use that no doubt so that one stays. Just..going to install it within instead,again out of safety reasons.



Uhu. Pre used. I opted to block all the old holes off with a piece of 2mm anodized aluminium. Guess it tells where we´re going with this. Major holes needed have already been cut as you can see.
For JJ electrolyte "cans",for power as well as preamp tubes and so on. From a looks point of view this one´ll turn out rather similar to that Vortexion i just did.
Powerwise i´ll be using a pair of JJ 6V6´s..which brings that i KNOW that this thing´ll hand me like 28 watts or so outright. Cool enough in such a case.

Have to say. The transformers of this thing are sure sturdy enough seing the anticipated power... Hm..

[Racing]

Pushing forward. As you can see yourselves things has progressed a bit. I´m actually pushing both this one and that Elektrofon in para here..



Nope. One mere board won´t do it anymore. That simple,but the mainstay of it is there at least.



Yeah. All said and done with a pair of old 6V6´s in place but..suffice for measuring at least i guess. B+ is all in at approx 410VDC with a 5V4 in place which is about on par with what i expected. This at 22mA per 6V6. Picture i guess also tells how sturdy them x-formers are. Yeah..i guess this one´ll hand us what we ask as it gets to come final circle...

[Racing]

Uhu. Very little left. This thing will most likely speak again tomorrow.

[Racing]

After a bit of a hazzle with the output transformer we´re good to go in short. The thing works and works as intended. With a strat this thing friggin SCREAMS!

[ajaxlepinski]

Love your build posts!!!

Looks like you like to keep busy!

[Racing]

Thanx!



Look. So i picked up a bunch of old 6V6´s on our local e-bay right and as it turns out them read like new on my U-Tracer

So..a pair of old Brimars it is. First impression stands. Have had the chance to fool around with the amp a bit more and it sure delivers and it SURE is loud seing the limited powertubes,after all.

[Zozobra]

6V6's sure do get loud with that kind of plate voltage. I have a build with a pair at ~400VDC into an 8k primary and they ain't no joke. I wanted to run without a global NFB loop but it needs adding just to tame the amp and make the MV usable! I could probably knock the LTPI bias resistor up a little to tame the PI output too. With EL34s and the intended 4k reflected primary it'll be a monster.

[Racing]

Uhu.
For some reason many seem to fail to realize that given powernumbers are handed for given reference running conditions.
As you up plate voltage shit starts to happen as far as that,as long as primary and so forth follows. For instance..getting approx 100 watts out of a pair of EL-34 is certainly doable. GOOD EL-34´s will take 800 volts at the plates every day of the week and spit it out the other end. (..n inxs of that need be)

Speaking of which.





A while back i did this Italian Geloso 3298. Them 6146´s sees almost 900 volts on their top caps. Amp is quoted at 135 watts clean from the pair. Honestly haven´t measured,the thing is simply to loud for that live. In such a case i need to fab a fresh loadbox..and sort of nevermind as the power´s there and then some.

[Zozobra]

As ever, draw the load line and see if it's remotely sensible

Those are some interesting tubes from looking at the data sheet. The screens looks to be pretty weak given their low power and voltage ratings. I guess the need for such a big difference in plate and screen potentials is dipping into dual rail territory and the top cap is stop arcing at the pins. The flyback voltages must be something!

[Racing]

Agreed.
Sorry to say the "art" of reading datasheets seems to be....less widespread? TBH..i can appreciate that hobbyist don´t really care or mind but the issue,as i see it,is that LOADS of techs are just as bad at it. That OTOH is bad...as in REALLY bad.

I guess you´re aware that i´ve got a couple of tube testers around. That brings that techs from around show up to have tubes tried and tested. All good and i´m all to happy to help, but when i ask them to interpret the info of a datasheet they look like one legged chicken. Even more so when i show them the info handed by the U-Tracer of mine for instance.
Not cool.