Geloso G.229/6

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Yes. Yet another one. This time out the half fabled,to us nerds,model G.229
What´s so special?
Well,first of all it uses a transformer for phaseinverter...and in turn it can be run via 6V car batteries...through what´s known as vibrators (DOH!!).







That said why is it that the Mr Handymans of the world can´t stay the F away from these old Gelosos when it comes to paint.? Seriously. Why the F is that?
Not that i care all that much i´ll spray paint the thing red all said and done anyways and looking the way it does sure affected what it fetched all said and done too...

That last pic btw. Take a look at that thingy to the left,at the rear of the amp. That´s the stock voltage selector missing it´s insert and what´s been done is that a piece of wire has been set to replace it. THAT`S electrical safety for ya! Right there! Here in Sweden that means 240VAC mains exposed...Cheers!



Right. So this thing looks a little off mark vs other Gelosos of the time under the hood. Them black steel thingys there in the middle are old steel tube 6L6´s. To the left of them the 6V6 that runs the interstage transformer..



TBH i´m still a bit weary as to how this one has been modified,cause modded it certainly is. Notice the absence of the tube rectifiers... Hm. Future will tell i guess!



In turn them silvery things there are supposed to be the two vibrators...sure don´t look like it to me!

Well. One hotrod Geloso G.229 coming up. Eventually.

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WHY is it,for the love of GAWD,that some people just can´t leave well enough alone?!?
´Cause i´ll tell ya what... MrHandyman had a field day this time out. FRIGGIN IDIOT!

That there..is what i took delivery of. All good i guess. At least at a first glance. The 229 is a rather interesting machine really. First up it uses a single ended transformer for phaseinverter and in turn..a couple of "vibrators" to be able to run the amp off of a 6V car battery. Yep..there was a 12V version too... Now..it lacked it´s ONE powertransformer (the one for the DC run side of it) and in turn the vibrators..this i knew right off the bat.



Right. So a pair of old steel tubed 6L6s. Cool enough but nothing that i´ll use seing that these 6L6´s are REAL limited as far as performance. Most of them steel 6L6´s are rated at 11w per tube...which is kind of pointless isn´t it.



So. That small transformer there at the chassis ledge is the PI. Driven by a 6V6 no less.



Right. So already at this point i should have known... Them two holes there are really supposed to hold sockets for two pcs of vibrators. These had obviously been scrapped and...replaced by a pair of "can" electrolytes.
Now..the farther one...look at how it´s secured in there. A friggin washer of sorts has been wedged in there to keep it in place. That said be aware that these e-lytes hit ground through their chassis. The layer of paint ALONE tells the friggin story!
Yep. Mr Handyman has had a field day with this one...*shakes head* . Then..look at the max voltage allowable for ´em...that´d be pointer two for little ol´ Racing...



Then. The 1000€ paintjob. Reason for all that paint became totally obvious as i hit it with the 60grit...cause what they´d done was paint over craploads of rust. In short..this one needs to be taken down to bare metal. Period.



*sighs loudly* Well. There´s a hackjob if you ever saw one.



We knew that the PT had been replaced. All good i guess. For some reason tho the "tech" had added a choke. Mark..that voltage enters the choke AFTER a "sag" resistor and mark that this point is NOT served any capacitance what so ever.
Now.
The PT runs its HT as 265-0-265. Ie;it´s centertapped. Look at the pic...the tube rectifier had been completely taken out of the equation and a set of 4pcs of BY-127 diodes had taken its place. Be that as it may Mr Handyman had omitted the centertap completely and run the diodes off of one side of the HT and the centertap. That´s one way of doing it i guess...but it sure ain´t right. Friggin idiot.
Speaking of which the PT installed strikes me as being of the same brand we saw in that way smaller Rodec amp i did recently. Deadringer even,just way larger.

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The signia cleaned right up with some 800 grit and water. No harm no foul. The choke Mr Handyman had installed turned out to be a 4H unit,which is usable somewhere down the line i guess.





That´s high performance craftsmanship for ya right there!!! TBH Mr Handyman must have been dead drunk at the time cause..that´s the only reasonable reason for it being that skewed. There´s no other explanation for that hackjob.
In turn...to deburr must have been a class the idiot missed out on. That there needs to be handled,one way or another,as the PT has to go. 265VAC simply leaves us with to little B+ all said and done and..well,that there sure as hell ain´t up to my standards.
I´ll tell ya that much.



Then...for the prime suspect as to why the stock PT had gone into orbit. Performance fuse by fuckup...talking of idiots. It gets better tho..there´s TWO fuses. The other one had the mains safety ground wired to it!!! WTF?



Yep. The phaseinverter transformer. For some reason it´s installed with spring loaded screws? No idea why...

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As current day n era swedish paint stripper is a friggin joke i opted to use washing acetone and elbow grease coupled with a stiff brush. As the paint comes off...i still have to sand that there as there´s as much rust around as there is.



Might not look all that bad,then again this is AFTER some serious sanding. This one really needs to get to bare metal. Only way to handle it,sry to say. OTOH the amp being as old as it is the sheetmetal is most certainly not from revamped steel...meaning that what you see is what you get. Ie;just get that rust off of there and done deal.



For better for worse the materials i can reuse this time out is...limited. EVERYTHING has been run into the ground. Down to for instance the ceramic octal sockets. Then again..got a few plastic Geloso ones surplus so...we´ll handle that too.
The stock voltage selector was even unusable as the paint used had fused with the plastic...so replacement there too....and the list goes on..



Right. To fit the bill. A PT out of an old Dynacord MV-45. Hands me approx 420-450VDC B+ all said (depending on type of tube rectifier used) and..two separate heater windings,a bias tap and what not. This one then to be hooked to a stock Geloso voltage selector...
As it turns out that gorilla´d hole...i basically just need to dress it to make this work. For the better.

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As always it´s all in the details. Need to replace them M4 screws for speaker out with regular plated ones. For looks only.
Fuseholders will hold up..



Had my mind set on reusing that one ceramic socket,for a tube rectifier,but...no dice. Guess you can all see/notice the crack..
Well,got a few original Geloso sockets surpuls...so we´re still all good.



Yep. Phaseinverter transformer and output transformer.

Got to dress that god awful looking hole for the PT in the chassis...good enough. Die grinder made short work of that so.. New PT is in place. To the point where i´ve at least hit the chassis with etching primer one first hit.

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Now,that´s transformation for you. Right there. There´s something about...them chassis getting handed a dab of paint and being bolted back together...

As stated i cleaned that horrendous hole up best as i could. At least turned out decent,altho the hole is like 5mm to wide for the PT used. Well..you can´t have it all i guess.

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Got the PT primary wired up. Nothing all that much to it really. As i use an IEC jack i get away with using a mains breaker that cuts just one of the two wires. Around here it can be either phase or zero so...



Even though this particular PT is wound for a GZ-34 rectifier tube i have my heart set to at least TRY a 5U4. Point being that the GZ-34/5AR4 takes 1,9A for its heater while a 5U4 takes 3A. Therefore i opted to install some rather heavu duty wiring from the PT to the socket. Practical readings will tell. Took a few readings off of the secondary side of that PT and i´d say we´re good to go. Approx 365-0-365,which as far as i´m concerned is what the Dr ordered. In turn two 6,3VAC windings for heaters and in turn one 5VAC for the rectifier and then a bias tap that hands med 58VAC raw.



Sorry to say one of the three octals is simply to small in diameter for its hole rendering that one could pull the entire socket out of there when replacing the tube-or for whatever reason remove the tube.
Ie;it´s a no can do so...fresh Beltons it is. Pity.
Anywho....the output transformer is back in place as you can see. ATM that brings that my biggest concern,or doubt if you wish,is if to keep the intermediate transformer (a smaller regular single end transformer)for PI.
Have played around with that before and..at that point i tossed it out of there as i felt i lost high end and overtones.

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Mimic´d what i did with the 211. Ie;two wires from the tele jack and..rest is history. Ground reference is through the metal jack. These "later" Geloso output transformers are extremely versatile and can basically cater to any output impedance you can dream up.



Stock these amps are basically filled to the brim with transformers. One of them being the one to handle what´s handed via the stock vibrators as you run the thing off of a car battery. Well..that one´s gone since long and altho the new powertransformer is of the type that´s "cut" in there´s a bit of room between the PT and output transformer. Holes were already there so...

Pushing forward there is a matter of picking a choke in turn. Haven´t decided yet,but the options are for either 4H or 20H. In turn i´ll START OUT using the phaseinverter transformer and it´s 6V6 driver. We´ll see where that ends up.

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Right.



An old SE x-former to work as an inductance only. Approx 4H worth. In turn the switched transformer that hands me 5VDC to control the optos...to come.



The bias board in turn. Hands me a max of approx 75VDC,which is more then enough,and as usual separately adjustable for respective powertube. Now..keep that in mind...



Not all that much to add really. What´s needed outbound in essence.



Yep. Up and running. B+ is all in with the 5U4 at approx 425VDC@35mA per powertube. Figures i´m happy with. After the choke each g2 sees a 47V/5W zener in series with a 100 Ohm resistor in turn. Works..what can i say?



The preamp. Nothing you haven´t seen before i´d say but..notice them 100nF caps at the boards end. As i´m to use the stock transformer used as phaseinverter AND i want to couple that with individual bias adjustment AND a PPIMV...
Stock the transformer has a centertap where the bias voltage is introduced. That will be omitted. Instead each signal will be headed for the PPIMV pot and from there return vs g1 of each powertube VIA them two 100nF capacitors. In turn negative grid voltage for each powertube will be introduced at that same point.

Going to be interesting as hell to experience the outcome of that PI x-former..

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Big gun time. That there is a Telefunken red tip from my private stash.



That last radial capacitor there i just jumpered in to get the thing fired up. That 6V6 for the interstage transformer sure digests a bit of power,so i need to take a look at the size of the dropping resistors.



Not all that much left to do. Wiring for the pots...the tonecontrols..and that´s about it. In other words we´re closing up on showtime...

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Then...then there´s times when one feels that progress is slow. None the less,progress. Wiring is tedious..but needed.



Yeah. There´s a wire or two alright. But they all serve a purpose. That said they´ll,most of them,get hid by the stock EMI/RFI shield when the time comes.



Uhu. A number of needed switches had been added. Like the wiring. Needed.

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Right. So here´s the bottom line on that using a x-former as PI ordeal. I was wrong. My previous experiences on the matter was solely a matter of the wrong x-former vs the impedances needed. That simple,cause this thing works a friggin million bux!
However..a more in depth explanation might be in order...well,tag along..



Fact is that this has simply come together like one giant jigsaw puzzle. In short..i´d say it´s time to revert to handing some parts paint again..



So amp is dual mode right. Either 2 or 4 gainstages,the latter then per definition highgain (4 stages or more). That said it STILL doesn´t react as one would expect,partly due to the very limited amplification factor of that 6V6 that runs the interstage x-former. Iow the distortion offered by highgain mode is very very controllable. Full of overtones and what not,but this in a REALLY good way!
Fact is that from the perspective of hum and hiss,due to the above,the amp is beyond textbook clean in behavior. In lo-gain mode you to the letter have to lean with your ear into the cab to hear the amp run...and then barely so. In highgain mode hiss of course increases a bit,but still WAY WAY WAY less than you´d be used to.
What´s more...this thing OOOZES of stringseparation! Damn!

However. The main idea behind that interstage transformer really is that it is able to push way more current then your normal pick tube PI can. That said..i´ve tried the amp in both with and without a PPIMV installed mode. With the PPIMV in there a part of that "more current" idea goes out the door for natural reasons as we leave that current somewhere to escape..but TBH it´s of minor consequence at the volume levels used. Volume then being along what at least i consider normal rehearsal/gig volumes,Ie...like maybe 95dB or so. Mere truth is that at those levels ...difference between the two modes is way less than what to expect. I guess the whole "push current" setup comes into play as you start to lean into the amp,and at that rate that there transformer should be able to push the amp into class B2,seing the available current and all.

After talking the setup over with my mentor Aleks we agreed in turn that the cathode resistor value for the 6V6 needs to be adjusted a bit. As is i´m simply running that 6V6 to FAR from the edge. I´ll solve that tomorrow,but that said let it be known that this one´s been a REAL eye opener to me! Got to play around with the amp before heading home like an hr or so and...this thing RAWKS! Let me tell ya!.
String separation is simply out of this world! That said it stands to reason that this isn´t exactly the most simple amp around to play either! Sournote 101 to those that don´t master the guitar in short.



Another thing where it turned out that the "window" was rather narrow was the amount of capacitance across the 6V6 cathode resistor. Tried a whole bunch of figures between 10µF and 330µF and the truth is that in this case..less was more. Ended up using 22µF as bottom end otherwise had a will to "fart out".



E-lyte to the left is most certainly still just temporary...however the rest of the amp really came together!

Alls said and done i came to try two different tube rectifiers. A GZ-34/5AR4 and a 5U4. Choice became the GZ,which elevated voltages approx 35VDC or so. For the better.

Now. Of course there will be a bit of tweaking but on a general whole this one sounds and plays absolutely fantastic right out of the box! Gig ready if you wish cause this one i´d bring onstage ANY day!

In summary my thoughts on an interstage x-former was wrong in short. To the extent that you will see me revisit this,and you can take that to the bank! To the point where i question why not more "high end" builders use them. More expensive then a tube? Of course,but who cares at that level.?

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Alright. So some fresh chickenheads. 5 large,and then 2 small ones for the tonecontrols. In turn some stickers to tell what does what and why. Ontop of that a fresh GZ-34.



That there is a trim capacitor. Range from 2 to 47pF. Something i rarely touch upon is filtering when i put my amps together and many get surprised when i tell that i tend to fool around with the signal as little as possible. In short it mainly comes down to them James controls,with all their bells n whistles.
However,when one starts to fool around with highgain setups AND a "global" tonecontrol it is more the rule then anything that the overtone spectre changes and if that isn´t handled one way or another we have ourselves an amp that´ll howl like a god damn wolf at midnight.
Most tend to combat this by various implements of small sized capacitors which are installed across plate resistors and god knows what else.

Well. If you do like everybody else you end up with an amp that sounds just as average. A physical property of a small signal triode is a capacitance within the tube known as the Miller capacitance. This is usually something we do our best to overcome (low gain circuits) as it will cut top end. It´ll work in liason with grid input impedance and what not...(Pentodes,like the EF-86 the 6SJ7 et al does not suffer from this.)
Well. Since a while back i´ve opted to let it work FOR us instead WHEN in highgain mode-s. What i do is that i install a trim capacitor between the anode/plate and the grid and this capacitance will work together with the Miller one in such a manner that the two values are multiplied. From a practical point of view this means that them there 2pF to 47pF TIMES the Miller will hand us the total capacitance that will hinder the absolute top end and the amount of capacitance will tell down to which freq.
In doing this adjustable it ALSO brings that this can be tailored to cater to the "distortion span" one decides on.
Now.
In THIS particular case that means that all that was needed was a tad of capacitance for the 3d stage grid n plate. THIS case as this amp lacks the issues that normally follows when we push all of that signal into a common longtailed pair phaseinverter. As we´ve touched on THIS particular amp uses a 6V6 driver and a transformer instead,bringing that both the issue and the amplification rate of THIS phaseinverter doesn´t call for all that much to calm the entire thing down.

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Closing up on full circle. Compare that there pic to the one ontop..

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Right.
Been at this one a little over the last few days and have to say...it IS an amp apart.. Truly.
As much as it is highgain per definition it is EVER so usable. Goes to tell how much a certain type of phaseinverter really impacts a given design i guess.
So.
I got to use the thing at a rehearsal the other night and it struck me..i could basically dime the dials and..still not anywhere NEAR over the top,which got me thinking.
Let it be known that what we play in THAT particular band is late -80s to late -90s style metal. Me being the lead guy. Is there enough distortion then? Well,the correct answer to that one have to be... i dunno.
Point is that this amp produces its fair share of distortion alright..but it never becomes "in your face" or..."mud". Could it use even more? Yeah i guess,but the point here is the amps absolutely INSANE separation.
IOW..amp kind of fools ya,and at that demands of you that you know what you´re doing. Hm.

At wide open though it had a reaaaaaaaaaaaaaal slight will to go into oscillation,so...needed to suspend the socket for V1.



So. Said and done and it was exactly what the Dr ordered. Then...more distortion? Should i add a fifth stage even? After debating that with myself for a while i came to the conclusion that...no.
What i can´t handle from that respect with 4 stages i sure as hell won´t with 5 either.

So what i did instead was reset a few resistor values. I UPPED the voltage for the preamp and in turn replaced the 100k plate resistors of stage 1 and 2 with 220k ones. In turn tossed yet a few trix at it and...voila!



Yeah. We needed one of those too. True enough.

This amp has turned out to indeed carry a character of its own. ALL of you that have played a highgain amp knows this one cause...as soon as you stop playing your pick hand automatically reaches for the volume control of your guitar...to keep the thing in check right.
With this amp...no need. Just mute the thing with your palm..and you´re good to go. Remarkable. That coupled with the amps ability of string separation brings for that look on your face a minute or so in that.... -"WTF?"-...and then you just stand there staring at the thing.
This also brings that the amp is very direct. To the point,sort of.

In other words this is by any means NOT an amp for the newcomer. It ALL stands out. It´s that simple,which makes me wonder how one of these PI setups would work with that small signal pentode design of mine.?
Future will tell i guess.

Video flick time.