Geloso G.60?

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Geloso G.60?

Postby Racing on Fri Jun 24, 2016 11:58 am

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Here´s the deal. We´ve been debating what this is. At first i,mistakenly,thought it was a G.29 from way back but that fell through soon enough.
Spoke to some more or less knowledgeable Italians..who were just as puzzled at first really,but after REALLY diggin through old Geloso references we agreed on that this is most likely a modified model G.60.
In fact,it´s the only Geloso model of the time that comes even close. Some debated that this might even be a prototype...yeah well,you tell me.

No matter. It was used up and defunct and that´s how i picked it up on Italian e-bay.

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From a pure layout POW it reminds a bit of my old G.27,that i still have,just that...it SHOULD use a single end intermediate transformer as phase inverter in G.60 form. This one doesn´t.

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That there is what showed up at the doorstep of the shop of mine. At least the box didn´t contain bricks! :lol: It had survived the trip in reasonable shape,only thing that had happend was that a few of the index pins had broken off. Easy enough to remedy with some instant glue.

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It is a rather odd build. That there is a 5U4G and a 5Y3 to the right...and next to them a pair of old 6L6G´s. Beutiful glass IMO.

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Someone had sure as hell been under the hood of this one! Make no mistake. That there is NOT how Geloso used to do it,in fact it is MORE proper to the looks.
In turn it uses "euro" style e-caps to boot.

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Sports two chokes. This one for the bias circuit. Yep...it uses negative voltage for g1.

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Here in turn one of them age old diodes,for the bias circuit.

Anyhow.
After checking integrity of the e-caps and tossing a few bits and ends at it it was good to go. Or..try at least. Fired her up,and she worked alright! However..output i´d say was along the 2-3w mark or so.
Fiddled around with various solderjoints for a while and...presto. We had full power.

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The flipside of it.
Age wise when talking Geloso that there typical Geloso output impedance chart tells the story. It´s only the early ones that use the 6 bolt type,rendering that this is an early amp. Ie;made in the -40s or earlier.

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The electrolytic capacitors onboard are older offerings no doubt. As to how "stock"...no idea. However.. It is SUPPOSED to use a SE transformer for PI and..it doesn´t. Instead we find a regular 6SN7 setup as a concertina/cathodyne.
Now. This becomes imperative cause that brings yet another octal socket and here´s the twist.... That added socket says Geloso in relief too.
What i´m saying is that this might very well be an amp that was modded BY Geloso.

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I dismantled it in sections so to say. This then being the tagboard. Ducati branded coupling caps tells a bit of the story too as later made Gelosos used their own branded dittos.
In turn some of the resistors are NOT Geloso. As you can see they at least remind strongly of the variety for instance found in old Vox amps et al. Peculiar to say the least.

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This then a close up of the odd man out. Still marked Geloso tho...

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This then the control section of it. Nothing all that much to add. Note the use of shielded wiring.

Anyways.
The power transformer has a few peculiar odditys to it. Twin 5VAC´s for the two rectifier tubes. Then one "high voltage" AC winding and one "intermediate" AC winding.
The former of approx 340VAC and the latter 265VAC. The HT one runs the plates of the 6L6´s ONLY and the lower one in turn the rest of the amp. Atop that we´ve got a couple of taps for the bias circuit and in turn the regular 6,3VAC for heaters.
Not exactly the cheapest way of putting an amp together boys. What´s more that PT is absolutely MASSIVE in size.

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So. Apart the entire thing came. I picked up a number of fresh Beltons for it but...i´m a nerd right.. :mrgreen: :lol: :lol: and see..as it turns out them stock octals all say Geloso. So i took to taking them apart and cleaning them out. Basically just for the hell of it.
Came out a million bux tho so no harm no foul and this way a part at least of the amps heritage still shows.

Btw...

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That there is what a stock G.60 looks like compared to mine. Guess it tells the story huh.

So what then sets it apart,apart from the different PI setup? Not all that much TBH. On the contrary there´s a number of points where it is a deadringer for a G.60 why...yeah well. It IS a modified G.60 to the best of our knowledge.

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Right. Cleanup. Guess "Cambio tensioni" tells the story huh :lol: . All the little things has been picked apart and cleaned out. Hopefully for yet a number of yrs of trouble free service.

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But. Seing how modified the amp is anyways i´ve opted to bring it into the 21st century. That for instance brings the install of a number of fuses,and IEC inlet aso.
I opted to "reuse" a few of the holes already drilled and install the panel mount fuseholders there.

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Uhu. In the same manner as the G.27 of mine. Why redo something that works?
As you can see the chassis has been sanded down...that old paint is simply not an option anymore.

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Choices. Many of these old amps uses a pulldown from B+ vs chassis ground to keep the thing under control voltage wise as the tubes heat up. As the rectifiers are directly heated that means that they come up to stand sooner then the rest of the tubes and back in the old days this was handled by regular pulldown resistor setups. In this case 10k+10k of 25w a pop.
Sure. I could have just as easily fabbed a "powerscaling" setup of sorts but opted to run with the old ways..i guess out of respect for the original design to an extent.
Installed in such a manner that the heatsink is approx underneath the powertransformer. That way noone will burn himself fiddling around with the amp.

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Well. You´ve seen that one many a times by now. Opted to drill what i could before handing the chassis some fresh paint.

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If an amp this old is to be actually used even the little things needs to be considered. Like a fresh mains switch for instance.

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...like fresh main smoothing caps...

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You guessed it! Red it is. Italian amp..."rosso"..that simple. Here in the wet still.
As it turned out though the applied paint reacted with the underlaying,what i presume,nitro paint so..out the actone came. Cleaned the entire thing out and started all over,this time out with way better end results.

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A few layers of clearcoat and ample time to set n dry it was time to reinstall the various parts again. Of course then cleaned out and in order too..
That said...DAMN that is one large powertransformer! :shock: :shock:

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Uhu. Novals,´n yep. As usual in my case the first one rubber suspended. No matter where this will go doing so is always a good idea IMO.

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Reeeeeeiiight. Here we go. Starting to look way more business. Pilot light is a "reuse" as well,an old Fender one.

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This in turn out rear. Still need to figure out what to do about that hole left by an octal socket. Stock it is the hookup for a stand alone "preamplificatori G1".
Either a block off of sorts OR..install an octal again,just as a dud in that case.
Racing
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Re: Geloso G.60?

Postby Racing on Wed Jun 29, 2016 12:55 am

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I debated with myself if to paint the chassis within too or not for a while and...i guess you gather the outcome. Nah,but really. The innards are all about tech. At least IMO.
Proper layout of components and wiring,of course. That makes for a difference,paint-as in regular paint,does not.
Stock these amps lack out in a major way as far as fuses why that has been added as noted previously.

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Basically most of what was in there gets replaced. Overdue to a large extent IMO. Putting heater wiring down to me is by far one of the most tedious jobs when putting an amp together,the more reason to have it done correctly.

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The wiring for the bias setup still not hooked up but..you get an idea at least. Need to fab a tagboard for it before i go any further on that one.
That brings setting how i want to handle the whole ordeal with bias voltage ´cause the stock winding won´t suffice for running 6L6´s outright,that much is for sure. Then again..i decided on running the amp stock from that aspect...ie;use two rectifiers and thus one rectifier for plate voltage and one for the rest of the amp. That brings that screen voltage will be limited and thereby..the need for bias voltage will plummet accordingly.

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Yep. Used two existing holes. Correct. Yep. Needs more e-lytes to handle what´s up.

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So. All said and done i opted to reuse one of them ceramic based "towers" from "Dr Oetker". Worked out just fine i´d say. Seing the limited g2 voltage i just installed 100 Ohmers to keep any RFI/EMI at bay.

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Uhu. A small piece of the stock tagboard actually got reused after all. That there is the bias board and yep...individually adjustable bias. Of course. All said and done it turns out that the whole contraption works a million bux.

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So. What´ll be "new" this time out is the differed plate and "rest of the amp" windings. Stock the unit uses a choke first thing for the "rest of the amp" setup,and the choke per se is reused too.
However now it enters the picture between g2 and PI. The reason for the choke,most likely,is ripple control. All done and well but..i reasoned as such that sans the choke vs g2 i´d get a snappier transient response out of the amp. Right or wrong? Remains to be seen i guess.

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..and here we go. The by now tried and true preamp setup. A few values vary...but as a whole a setup i know to work and work very very well. Now..the amp lacks a whole lot still but as of today it is up and running,as far as the electrical side of things. Voltages seems to be approx where i want them to be so..guess we´re all systems go to continue.

When one reads up on the G.60, Geloso for some reason quoted these at a whopping 60 watts. TBH i have a REAL hard time seing that happening with the involved voltages and values at hand. Then again..i may be wrong. Has been known to happen before.
Racing
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Re: Geloso G.60?

Postby Racing on Thu Jul 14, 2016 11:09 pm

..and on the story goes...

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To an extent...it´s about the details. The difference between a good build and and outstanding one,IMO,is in the details. Fresh fasteners. Black such..aluminium colored transformers,red chassis...and black fasteners.

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An IEC jack is always a good idea. That and added fuses..in turn the stock voltage selector,albeit "overhauled".

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That done,in simple terms,we´ve got ourselves an old Geloso G.60 that is up and running. Roaring its friggin heart out like it was going out of business.
There´s still a few snags tho,to me that is. These units were quoted at 60 watts@9% distortion. 50 watts@5% (which to the human ear is "clean" with a tube amp). Now..put that into context.
That G.225 in the other thread sports an about as large power transformer. This one..a HUGE one..but at a lower B+. Or more to the point,only thing fed by that part of the winding is the plates of them 6L6G´s. At approx 430VDC or so.
The other rectifier tube hands the rest of the amp,the screens of the 6L6s incl,365VDC and down... Put that up vs the G.225 that runs approx 480VDC B+,one rectifier only-albeit a powerful one.
The G.225 is quoted at 30w@5%. What gives?
I´ll tell you what..them stock RCA 6L6G´s in there tho..are tired. Maxing the thing out i saw like 33 watts maximum. Swapped for a pair of used 5881´s and...power was up. Big time.
Hm.
That the 225 in turn puts out way more then 30 watts in turn is utterly clear. I have a hard time getting my head around this.
Anyways.

The power is there..with both amps. Now just to extract it.

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Yep. Hood of it needs paint. Will have to wait a few days until the damn rain comes to a halt around here. In turn i´ll top them both off with one of them old "fender style" carrying handles in brown leather.

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This in turn...is a switched power supply. For those curious enough..google is your friend. What this hands me is 5VDC to run any and all opto couplers i see fit to control the amp.
I´ve been around the block with this,to say the least,and what i´ve arrived on here works and works VERY well. No frills,no drama..it just simply does its job. Period.

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That there in turn is a rather elaborate James network for tone control. Wide you won´t believe.. It can make the amp go from "Fender clean" to mayhem....just dial in what ya need..

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That there in turn is what that 5VDC supply feeds. A number of H11 optos. Mark that i run the signal THROUGH them,and the truth of the matter is that it friggin works a million bux. That simple.
Upper pic is of the dual PPIMV control and the lower one,as you can see,is of the entry jack and hence..it´s the mode control.

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No. Noooo..... HELL NO even. It will NOT get Marshall knobs. It´s just that ATM about every vendor in Sweden is closed for holliday/vacation..and them there was what i had around to be able to see what´s dialed where.

That said.
In lead mode the amp is nothing short of fantastic. Magic. Brilliant. It roars along like you won´t believe. The "normal" mode though needs a few trix tossed at it. A bright switch for instance...

What that brings though is a sort of question.
See...in essence this G.60 and that G.225 are very similar amps. The 225 roars too..just differently,and i wanna figure out why. Sure..the tube setup differs,but have in mind that the 6SJ7 entry..vs EF-86....in reality about same same.
Same thing applies for the two pcs of 12SL7 vs the two pieces of 6n2p´s. From there on out..main rectifier tube..same. Powertubes-same. Voltage for the PLATES differ,but from the PI onwards..same.
Something is eluding me here.
Hm.

For starters at least i´m going to play around with the components for the phase inverter tomorrow and see where that takes me.
Racing
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Re: Geloso G.60?

Postby Racing on Sat Jul 16, 2016 9:16 am

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Right. So a brightswitch was added across the gainpot vs the phaseinverter. Just what the Dr ordered i´d say. To be engaged when in "low gain" mode mainly,but adds a certain something when in high gain mode just as much.
220pF in series with a 10k resistor.

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Then...yeeeeeeeeeees. Just..... yeeeeeeeeeeeeees. Weather was in our favour yesterday and this there is the outcome. A rather far cry from the busted up and run down stocker IMO.

Amp has a real nice character to it. A rather aggressive one with TONS of separation. The various switches around the James makes for a very "wide" amp too. Have in mind that with a James as you change the value of ONE component the entire thing changes face really.

Apart from installing that bright switch i fooled around with various capacitances between the plates of the longtailed pair PI too. Ended up using the bare minimum 47pF. Basically to dial out "bat level hiss.

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This pic basically to give an idea of looks with a carrying strap installed. What i´ll use all said n done is the sorts we see on -50´s era Fenders.

Replaced the 5881´s i installed temporarily with 6L6G´s again..this time out a pair in WAY better nick handing me an amp that was about as loud just with the character of them really old 6L6´s added to it.

Trying it out through my open back MAX box with a pair of British made greenbacks..bliss. Just bliss.. :jam:
Racing
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Re: Geloso G.60?

Postby Racing on Fri Jul 22, 2016 12:10 am

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As always it´s all in the details right. This...this is where we come full circle a 70+yrs later.
I present to you,Geloso G.60 Testa Rossa.
Of COURSE it needed the Geloso symbol on there!

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Yep. 4 doors no waitin´...

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Left to do is a brown leather carrying strap and then some sort of bottom plate for the chassis incl rubber feet.
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