Geloso 3298/220

Make it loud here.

Geloso 3298/220

Postby Racing » Thu Dec 01, 2016 3:56 pm

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Ran into this one on the Danish "Craig list" (sort of) out of all places. The 3298..220. 220 for it being setup for 220VAC inbound voltage only. Ie;no voltage selector.
Up until recently i had no idea that Geloso was actually imported to Denmark,but i stand to be corrected.

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Basically stock. The two axials each side of the x-former is by me. Measured the stock ones and they were shot. I picked this one up DOA. Reason is simple,this one´s odd even for a Geloso see..
It uses 6146 powertubes..run at approx 800VDC :derp: ! Rendering that a 3298 puts out inxs of 100watts with ease.

DOA alright. I installed an IEC jack and a panel mount mains fuse first thing. Mainly as the stock mains cord was a phase n zero jobbie...and running sans safetyground is a no-no with ANY tubeamp in my book. Checked various vitals and...well,the one powertube was shot to kingdom come for starters.
Not the end of the world as NOS 6146´s ain´t an arm and a leg. So i ordered a pair over gerry e-bay and done deal.

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As i replaced them e-lytes,which there´s three "stairs" of all in all,and fired the thing up sans the preamp and what not...i got a mere 560VDC. That gave me the creeps... Not a shot PT again! Now,please have in mind that this thing stacks two windings for HT.

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Well,no fret. It turned out to be a set of shot diodes and done deal. So i in a rather coarse manner installed a set of regular 4A rectifier bridges and let it rip. That made me end up with 880VDC running on that LONE powertube that was still alive. All good and a sigh of relief.

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If you look at the print on the farther tube you´ll notice it´s been run hard. Look deeper yet and you see how the plate has been discolored within its "corners". Sure enough,as bias voltage was applied ONLY it took a serious dive as it hit that tube. In short that tube is dead but..i´m just as happy no matter as it turns out the x-formers and choke all are good to go. In short the expensive stuff.

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Did i mention it weighs a friggin ton (for a Geloso that is)? It sure as hell wasn´t a cheap alternative when new. That there is the add-on x-former that runs negative bias voltage and the rectified voltage for the preamp heaters. The can in turn is the first one i´ve even seen with the text Geloso on it.

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Yep. The plates gets fed from the top. The connectors even sports the Geloso insignia and are of course ceramic ;D

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No wonder the thing weighs approx 20kg... That there is a couple of chokes. One for the "lower" HT winding and the other is for the bias setup. Ripple control gents. Ripple control..

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Danish importer? Yeah. The stock instructions for speaker out impedance had a sticker..which said the same thing in Danish.

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That´s the pair of e-lytes for the lower winding. Dead as doornails. Bin time...

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The powertubes sport a minor cathode resistor of 15 Ohms stock. That one was burnt to crap.. The common 15 Ohmer for various reasons i guess (noooooo..the amp is still fixed bias). As i checked the coupling caps between the PI and powertubes they were leaked like crazy so..i guess what has happend is that bias for that one tube was simply first out. Shot screen resistor,burnt cathode resistor and burnt tube. Done deal.
As that took effect it went on into the bias circuitry and thus yelled fire in the hole to the entire rectified heater voltage for the preamp. Hence the looks above.. cause you see...

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Entry tube sure as hell wasn´t any better off.

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As i now knew that all the transformers were ok i said to hell with it and started cleaning the SOB both out and up. Washing acetone and some elbow grease made all the soot within vanish at least. Soot,if you didn´t know,is imperative to get rid of within an amp as it is conductive.

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Have to say that the stock ceramic octals cleaned up real nice! That hookup there tho..no idea why Geloso opted to do it that way (that in the pic is by me tho) as pin 1-4-6 is supposed to be internally connected for the 6146?.

Well. A crapload of work to go before i fire this one up again (read-before the new powertubes show up). Needs to be done tho.

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As the amps is as heavy as it is i´m giving thought to that there this time out. Imagine a sort of Marshall JMP look if you wish. Cab is an old transistor one that i scrapped a while back. Amp is rather low profile so..it juuuuuuuuuuuuust fits height wise.
Y/N?
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Re: Geloso 3298/220

Postby NoiseNoiseNoise » Fri Dec 02, 2016 3:37 am

I think the original mesh cover looks really good, so I'd say no to putting it in a cabinet. This mother is going to be LOUD!
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Re: Geloso 3298/220

Postby Racing » Mon Dec 05, 2016 2:11 pm

Yep.
Real loud.

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Uhu. Per usual,a biasboard with individual adjustment. However... It also provides heater voltage,rectified such,for the entire preamp and PI and as such that needs smoothing too so..three of them there are intended to handle that.
As i replaced the stock selenium rectifier voltage jumped a bit so i installed a pair of resistors of 100 Ohms in para to make the voltage for each tube end up where it should (Ie; 50 Ohms total). That setup needs a bit of shrink sleeve and the radial e-lytes i mention need a dab of glue each.
Unorthodox to say the least but...whatever works,and works for the long haul right.

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...right.
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Re: Geloso 3298/220

Postby Racing » Sun Dec 18, 2016 4:25 am

Here i was thinking that the delivery of those fresh powertubes was gonna be fast...
Not so i guess as it turned out that the seller resides in Hungary! :D

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So. At least the embryo for a new preamp. Boosted by the success of the DuKane i thought i´d push that evelope.

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The faceplate of some of these -60s Gelosos are so-so IMO so a fresh one was fabbed. We´ll see where it ends up.

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Uhu. What i have in mind means that the turretboard won´t suffice. If you haven´t noticed yet ONE socket has been added thus far. THUS far.
Speaking of which.
A while back i picked up some plunches. A 22mm one for novals and a 30mm one for octals. In turn i´ve got this rectangular one for IEC jacks. If you´re into putting amps together...worthwhile doesn´t start to tell...
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Re: Geloso 3298/220

Postby Racing » Sun Dec 18, 2016 3:23 pm

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Hm. I need to get way more elaborate than that...
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Re: Geloso 3298/220

Postby Racing » Tue Dec 20, 2016 3:26 pm

The mancold from hell has infested me...so progress is real slow ATM. >:(
There. I got to bitch a bit.

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Yes. A socket for an ECC-82/12AU7 was added and..components needed as well. All in all we´re getting close to done as far as that goes.
The actual jack for the loop you can barely notice low in the pic.

Ya know..it might look like this thing´s roomy but..seing all them transformers and accessories...not so,why planning ahead when placing stuff is required. No doubt.

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Well lads. As far as i´m concerned that is one of the few uses of tape i see within an amp. To keep the wiring in check while the glue to keep said wiring from dangling about cures. End of story :D .
I installed yet another bottle which at 12V means yet another 150mA of load. Well,i replaced the stock selenium rectifier for the rectified heaters right and doing so voltage jumped a bit. So..installed 50 Ohms in series after the choke,which made voltage end up where it should be at approx 12,5V per bottle.
Well,as i added a bottle it turned out that all i had to do was get rid of them 50 Ohms and we were right on mark again :w00t:

Stock these things sport a 15 Ohms cathode resistor for the powertubes. AFAIK to make bias readings easier. Be that as it may i replaced the burned to crap stock resistor with a fresh one and added regular 1 Ohm ones per bottle as well.
High in the pic?
Yeah. The James network is ready for action. Need to dwell on that a bit as i want to elaborate the setup...will see where that takes me.
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Re: Geloso 3298/220

Postby salty » Tue Dec 20, 2016 3:35 pm

I really admire your work and knowledge.
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Re: Geloso 3298/220

Postby Racing » Tue Dec 20, 2016 4:42 pm

Thank you :)
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Re: Geloso 3298/220

Postby Racing » Wed Dec 21, 2016 4:41 pm

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Yup. We need one of those. That solution with them wires through the chassis...TBH it´s kind of grown on me. After all,how often do you swap output impedance all said and done?
Takes a philips headed screwdriver and that´s it. Nothing that can be intermittent about it. Hardwired in a sense...

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Yes. I´m aware it looks a bit clustered but...work in progress,as i guess you can see.

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We bought a set of new 6146s over German e-bay right. Turns out the seller is in Hungary...and from what it seems have ordered someone to F-in WALK up here with them tubes!
So. A pair,NOS,was for sale on our local e-bay...so grabbed those. Bought and friggin paid for.
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Re: Geloso 3298/220

Postby Racing » Sat Dec 24, 2016 6:19 am

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This is starting to piss me off a bit cause...here we´ve got ourselves a complete amp....and i STILL lack the powertubes for it.
Have bought two sets from two different places and NONE of them have come through. :fp:

Needs a bit tidying up and..have its shield installed. That´s it.

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Yep. Even the loop is up and running.

Merry x-mas boys!
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Re: Geloso 3298/220

Postby Racing » Tue Dec 27, 2016 6:16 am

FINALLY it seems that at least one of the sets of powertubes bought has showed up!
Going to pick it up later tonight.
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Re: Geloso 3298/220

Postby Racing » Wed Dec 28, 2016 1:12 pm

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Ok. So these guys showed up. NOS Siemens QE-05/40´s,or 6146´s if you wish. Now,when it rains it pours right... So in they went and i fired the thing up. Output power was low to say the least. Knowing all to well that i had gone over EVERYTHING else...output transformer primary.

Checked DC resistence for it and...90 Ohms from centertap out and in turn...11 Ohms. Iow one of the primaries was shorted,bad. :( .This sure enough explains the very limited output.

Now. 6146´s want to see a primary impedance of approx 8k at 750VDC.... So. Looked around the shop REAL heard and came to think of an old Dynacord Eminent II i had pulled apart which indeed uses EL-34´s at the same voltage. 750V,and at that voltage primary impedance need is about on par with the 6146´s!

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Head over heels basically i took to making that Dynacord transformer fit. Still needs a few touches.. But the point here is that i also came to notice that the voltage heading for the preamp was a tad over the top to say the least. The PI saw almost 480 volts for rail!
So. Hip hap i´ve put a 10k ceramic in there and sure enough...now we´re getting somewhere. Voltage for the PI dropped like 100 volts...way better.

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Now. There´s a point to that there..´cause see the plate voltage for those two 6146´s...is high. As in REAL high. It touches down at 870VDC under a load of 22mA per tube.
Hm.
...n see...

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At first the voltage out of the bias circuit didn´t suffice,so what i did was lower the resistor value for the first drop one. From 4.7k to 2,2k and that did the trick. Now i had full control of bias at least. ´N yeah...i need to clean that there up.

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The stock OT has solderprongs on it´s "outside". Ie,when you pick the hood off of the thing them solderprongs are exposed. Not so anymore,and that also brough a rubbet grommet-seing the voltages at hand.

Does the "new" OT stand tall vs its new task? Yes. In essence,yes. Amp is rather powerful,no argument there. If there´s enough for the claimed 135 watts tho...no idea as of yet. Will have to measure that i guess but before doing so i got to pick up the correct rating fuses for the amp. Stock has simply run low so i´ll handle that tomorrow time permitting.

Then for the looks of this thing.
I dunno guys. The thing here is that the transformers alone makes this THE heaviest Geloso i´ve worked on thus far. We´re talking 20kg easy here. The "hood" of this thing...sure isn´t the prettiest i´ve laid eyes on either.
I guess a pot of coffee is in order...and a sit.

Now will follow a bit of tweaking,of course. As is the two channels work and work rather well. As does the loop. Intent here is for the doom crowd to take interest,ie;fuzzy sound,and..i guess i´m half ways already at least.
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Re: Geloso 3298/220

Postby Racing » Thu Dec 29, 2016 5:24 pm

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Right. Tweaked a bit..and we´re certainly getting there. Let me tell you what...this is one LOUD puppy! Haven´t measured output power yet but DAMN this thing is loud! Out of a mere 2 pcs of powertubes
That´s 6146 for ya i guess.

Then..the looks of it...*shakes head*

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I´m gonna try. That there is an old cab for a Peavey transistor jobbie. Rather "low" to the build,to the point where the Geloso slides in just baaaaaaaaaaaaarely... Cleaned it up a bit and ..the handle you´ve seen before,so no news there. Plan on a faceplate a´la JMP...we´ll see where it takes us.

Will keep the Geloso insignia and...

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..add my brand new own. :w00t: Lasercut n all..
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Re: Geloso 3298/220

Postby NoiseNoiseNoise » Fri Dec 30, 2016 1:51 am

I still like the original mesh cover. :)
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Re: Geloso 3298/220

Postby Racing » Fri Dec 30, 2016 2:41 am

".....some men....you just can´t reach..."
:D :D
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