Geloso G.221

[Racing]

There was two of them in the bundle right and this is the other one. A model G.221 and truth be told i´ve had half an eye open for one of these for quite a while.
Not that there´s all that much different with them,just wanted to handle one in the flesh so to say. As you can see this 221 sure has seen better days too.

Seller,Diego,is a standup guy tho. Should be said.



For a few years there in the early/mid -60´s Geloso had this idea to install sorts of an aluminium plate "sticker" ontop. No idea as to why. As it´s a piece of aluminium sheetmetal tho it came right off with a little help from a heat gun. Glues and heat don´t mix all that well see so..



Yep. Basic,and see that´s the idea of mine with BOTH these amps when done. Have done a few of these Geloso "piccolos" by now and know what to expect so..one channel does it all. "Four doors no waiting",but..FOR a channel OTOH.
No frills,no bullshit. Just simple and balls to the wall tubeamps for rocknroll use.

Difference them between is that the 1020 uses EL-84´s out back and this 221 uses a pair of 6V6´s. Gonna toss yet a few differences at them but..one thing at a time.



Uhu. See,the socket to the far right is supposed to hold one of them "vibrator" jobbies that convert car DC voltage to AC voltage to run the tubeamp. Well,noone uses that anymore and the vibrator is long gone in turn. No harm no foul as far as i´m concerned.
That style of tube chart to is VERY Geloso.



After a thorough check i fired the thing up and sure enough. Presto,we had sound. Had to replace a few electrolytics in a kind of hip-hap manner but that done we were all good to go.

Now. As the vibrator is missing this means that i´ve got a winding on the PT that will HAND me AC voltage that isn´t used (stock it is the INPUT from the vibrator).
As it turns out this winding was of approx 18 volts and doing the math that made me end up a tad short as far as negative bias voltage. See,stock these things are cathode biased and...we´re done with that crap already.



So what i did was a so called voltage doubler. By installing diodes and e-capacitors in a certain manner i use the half periods in such a manner that the net effect is double what i´d normally see.
Whole thing works like a charm which means that i see a tad over 50VDC. Way enough to control the amp in its new setting when the time comes.



Right. As you saw above this one was about just as bad from a rust POW so...bare to the metal it is. Just as with the 1020 i cut the holes i saw needed before handing the chassis some primer.
Fabbed a block-off plate for the rear facia. Don´t want all them holes that people can stick their fingers into.



As the vibrator was missing and the chassis in turn is half roomy on the outside i decided to run a couple of JJ cans. Them two there will cater to what i need which leaves for a more sano impression within.



Uhu. Of COURSE an IEC jack. That and i recessed the voltage selector socket,gonna fab a "lid" for it too. In turn a mains fuse holder of way more contemporary design than the stockers.

[Racing]

Sure enough. The 221 got the treatment too.



Out back,apart from the modern jack n fuseholder,i came to fab a block-off plate as mentioned. Didn´t really melt into the surrounding tho but hey..can´t win ´em all!



Uhu. Coming together.

Again. I want to boost the quality of these old PA amps. Geloso really IS the real McCoy. No BS. Like in this case,you can grab an old rustbucket and with a minimum of effort turn it into a small screamer.

[Racing]

Started wiring the thing. Goes more into that than most believe i think.
Yep. Even a "discharge" resistor installed,atop the rectifier bridge. Choke is the stocker,just relocated.

[Racing]

Yes ma´m. We´ve got liftoff. After a couple of tweaks tossed at the thing i´d say we´re on par. Sounds the part.

[Racing]

Getting there. Still needs more clearcoat and what´s more i need to adress the bottom plate too.

That said the amp plays great. Going to try yet a few tweaks tossed at it and see where that takes me. All in all though already a really great little rocknroll amp with plenty volume ontap and does what it´s supposed to.

Rocknroll.

[DrQuasar]

I don't understand any of what you're doing, but I sure like reading your posts and seeing the photos. Would love to hear what it sounds like!

Do you reference a schematic when doing these restorations or can you open them up and take a look and pretty much know what's going on?

[Racing]

Thank you!

No. I try to form my "own" sounds,so normally the circuits used are my own. I have made "copys" on occasion but truth be told i get bored easily so...they are few and far apart.

These "simpler" amps of mine,i reason as such that someone heading in there down the line should know enough to know what he or she is looking at. After all it´s a mere two gainstages,basically used to the max,heading into a in this case longtailed pair phaseinverter. Of course i´d be happy to share the schem with a tech needing it,no two ways about it,but on a general whole these smaller amps...don´t need it if the tech knows what´s what and why. They´re that simple.

Simple though is not the choice of components. I´d say the mainstay of the sound and build stems from this. A mere change in one resistor value could easily "destroy" what the amp in case is capable of. That´s NOT saying that my take on it all is the end of all ills,it´s just me stating that it´s ONE way of doing it.
Mine.

The trick,at least in my book,is finding the recipe to make the amp responsive enough to be dialed "clean" and have a shimmer to it while at the other end be overtone prone with a lot of "cream" to the sound.
Many set them up to maximize amplification,i do not. Seing the amount of gainstages involved (add the phaseinverter as the amp uses a PPIMV) there´s absolutely no need to.
Better then to focus on tone, attitude and feel of the amp....and how it´s formed.

The need of amplification need can often be calculated "backwards" with great success. EL-84´s in push pull config for instance require around 11V to go full saturation.
A Longtailed pair phaseinverter often hands us an amp factor of around the 25-30 mark or so. That brings that a mere 500mV for the entry of it will suffice to push the amp to where it needs to be. In the case of the EL-84 it´s one of the few tubes that take really nice to distortion by themselves,so let´s for the sake of argument say that we send a whopping 5 volts in on the phaseinverter.

Now regard the other end. As we really dig into a guitar we can easily see 200mVAC out of it. If we ponder a regular ECC-83 these are referenced having a "mu" (amp factor) of 100 maximum. Per how we normally set them up in guitar amps we end up with a mu of approx 50 or so.
Right.
0,2*50=10VAC when everything is up to snuff. (There ya have the reason the normal channel of an AC-30 (which is ONE single gainstage) suffices to push that amp into distortion).
However.
We now bleed off signal vs ground to both form and control the tone,attitude and so fort of the amp before heading that signal into the next,second,gainstage. We in turn decide if we want our tonecontrols to perform before or after the second gainstage,in this case.
As you can gather we can achieve them volts needed inbound for the phaseinverter with ease,EVEN with a really low amp factor tube like let´s say an ECC-82 where we might se an amp factor of a mere 10 or so.

In short?
Designers and builders focus WAY WAY WAY to much on the glorified amp factor as you can basically reach distortion levels with any imaginable tube out there. Those claiming otherwise are full of it.
That leaves that he who dares wins...as different tubes (vs the ECC-83) might very well carry with them different properties,which CAN set the amp in case apart. Sometimes for the better,sometimes for the worse

Of course there´s way more to it than that but..what i bring up above holds water to the best of my knowledge and i wish that became more widespread.

[Racing]

@Dr Quasar

Seing you live in the US,here´s another advantage of most-if not all- Geloso made amps. They carry taps already in stock form to be run basically anywhere in the world.
There ARE a few exceptions. There were a few Gelosos made to cater to a specific market that ran only one pair of taps. I´ve seen these for 220VAC only,but then they´re so labeled. Ie;model number followed by a backslash and then the voltage it´s intended for.

All of the others tho carry a complete set of primary taps why they can be setup to run wherever really.

[Racing]

For the sake of argument. This is the finished amp within (sans the two wires heading for the pilot light). Clean,tidy and to the point. Not all that much more complex than the 5E9 Wproffitt just put together in another thread here. I bet a hobbyist like Wproffitt could figure this out need be.

Two 6V6´s at approx 370VDC and then a pair of small signal tubes,just used way different then in the 5E9 in case. Thus,more tailored vs rocknroll (read-distortion) at will.
Way smaller too. This little amp weighs in at a mere 6kg or so. Ergo an amp so small that it can tag along anywhere by it´s carrying handle to come.

[Racing]

Ok. So done deal,this is the net result. Happy? Yeah,happy.
Tossed a highpass filter at the circuit to make the thing more overtone prone as gain increases and i´d say that had exactly the result i was asking for.

These smaller amps,the thing is about on size with a Tiny Terror and weighs a mere 6kg,are real screamers when called upon. Powerwise they come to deliver around the 25watt mark when going balls to the wall and for most that suffices and then some.
Many are those that miscalculate their power needs in my experience.

Why this amp,and it´s soon to be sybling the 1020,comes to life. Simple,rugged,well performing small amps with one intention in mind. Dirty rocknroll.

Again. For those of you out there capable of building yourself...these smaller Gelosos are a no-brainer in my book. Transformers and hardparts in general are from the absolute top shelf.

[DrQuasar]

Looks great!

[Racing]

Thx!
In turn it plays as well as it looks.

[wproffitt]

Clean,tidy and to the point. Not all that much more complex than the 5E9 Wproffitt just put together in another thread here. I bet a hobbyist like Wproffitt could figure this out need be.

I'll accept your flattery! Racing, this one looks great! You're right. Even with my limited amount of knowledge (I've read a few books and built an amp), I actually understand most of what I'm looking at here. The math is still a little beyond me . This would be an easy little amp to work on, though. There's plenty of room to move around and things are laid out so as to be quite easily accessible. A couple of those more exotic rebuilds you've done (the bigger amps) are incomprehensible to me when I look at the pics, though!

[Racing]

Hey.
Credit where credit´s due. You did good in my book and i´m absolutely certain there will be new builds to come in your case.
Point is that building them becomes addictive.

[46346]

great to see what you're up to, Racing! i've been off the forum for much of this year, and it's good to come back and find one of your fresh projects. i always seem to learn a little more each time you post a detailed account.

i could actually imagine a coffee table book of your projects and write-ups - it's especially an adventure for we americans who don't get to see those amps and designs very much.

cheers!
eric