Not what you´d think tho. As some of you are aware i´m rather fond of the old Italian made Geloso amps. These were NOT guitaramps but old tube powered PA systems.
That´s not to say they can´t be used for guitar tho.
That there is a -66 vintage model G.3215. Nope,they sure as hell don´t sport sexy names,granted. That tho is kind of moot IMO as they´re from the absolute top shelf as far as quality.
At the time these were touted as "alta qualita". Top quality. They had a point,in hindsight.
Yep. An "18 watter". Ie;twin EL-84´s that all said and done are run around the 350VDC mark. Tube rectified via an EZ-81,then a pair of regular ECC-83´s/12 AX-7´s.
Note.
Gelosos were basically capable of being run anywhere in the world seing their various taps for inbound wall voltage,and this goes for even the REALLY old ones.
Got me a model G.27 that sports adjustable primaries...and that one´s from 1937. Go figure.
I´ve done a few of these Geloso twin EL-84 amps before,and the outcome is...one trick ponies for rocknroll. One trick you won´t believe tho..
Thing is that they indeed ARE lunchbox sized and weigh accordingly. Approx 6kg worth. In other words and amp that you can carry along anywhere with ease.
Anyway.
Post dropped the one in the pics off this monday. Ripped it apart,bought it in Holland,and the e-lytes were way passed best before. So replaced those right off the bat.
The stock tubes i checked in my U-Tracer and they all came out flying colors. Powertubes measured like 90+% a pop...not bad for tubes that has seen use since 1966!
Only damage really was the the voltage selector was cracked but a bit of superlglue made short notice of that.
Uhu. Typical Geloso. A metal tube chart riveted to the chassis.
Untouched.
Look. See how simple a layout? This isn´t hightech by any measure why overhauling one of these,as an absolute base line,is something i´d say anyone that owns a soldering iron can do. What you see there..that´s how complex they get. The busted electrolytic capacitors,that was in dire need of being replaced,are the large red and gold colored cans. Do that..and you´re basically in business.
Me?
Nah. I´m one of the real nerds remember?
So. To get a baseline and to see if the thing would still rock i just jumpered fresh capacitors in there hip-hap. Who cares,this was for bench work only right.
In doing so i just jumpered a pair of telejacks in there. They use rather funky jacks stock. Inbound they´re "Geloso" jacks (sort of looks like an XLR) and outbound these things can be hooked for any impedance you could ever dream up.
Yep. Real simple to the build. ALL focus has been put where it counts.
Power transformer with its markings. You can run it off of 100VAC to 240VAC. Just like that.
Uhu. "Tower of power". Indeed.
Uhu. EZ-81. Tube rectifier.
Uhu. Geloso. ´Nuff said,and as always it´s all in the details. That there is a bracket,sort of... It suspends V1 and thus works as an anti vibration setup.
It doesn´t stop there tho. The preamp and phaseinverter both are run off of rectified voltage. A stunt highgain amps touts as a feature TODAY.
1966. ´Nuff said.
(and this thing is anything BUT highgain!)
Yeah. Wiped the thing clean and started over. As they´re a rather simple setup this is done about at the drop of a hat to someone like me that does this all day long.
For the hobbyist...i´d say a few nights work. Beauty here is the simplicity. Two gainstages let to roar to hearts desire heading into a longtailed pair PI..then for the powertubes.
Yes. This´ll suffice for a REAL neat sounding piece of rocknroll. I promise.
The stocker sports a selenium rectifier for the circuit that´s bias voltage and the rectified heater voltage. This HAS to go.
Selenium rectifiers go old and as they do their capacity diminishes and..they can go boom. Not the end of the world? Wrong. Selenium is highly toxic.
Thus..we ALWAYS replace selenium rectifiers when we run into ´em.
In doing so,replacing with a common silicon bridge,voltage will jump a tad too and this needs to be handled as far as the voltage heading for the heaters. As current draw is basically static this is easily handled with a regular highpower resistor.
The stocker uses a number of inputs that ain´t needed anymore,phono jacks,so them holes left...tonecontrol. In this case a half elaborate James network.
Uhu. Things taking on their final shape. Take in the simplicity will you. That in mind be VERY clear on that this thing will take you into AC/DC heaven in a hearbeat,and then some.
Ok. So here´s a trick i use on lowered powered amps (50 watts and downwards). I install 25-47 volt zener diodes vs the powertube screens/g2.
There´s actually several reasons for this,but let it suffice to say that it´ll minimize "sag" (while not taking it out completely),it´ll make outright power jump and it´ll hand you a way more "direct" amp. Stunt works and works very very well. For RFI/EMI control i put a regular 100 Ohm resistor in series last thing before the screens.
Yep. They´re fixed bias stock,however not adjustable for amount. Install a regular 1/4w trimpot to make that a reality.. Hooked as a reostat vs ground within the bias circuit. That way,should the pot ever go belly up,all that´ll happen is that bias voltage will climb and finally make the powertubes run into cutoff. Ergo,just replace the pot and play again...
There ya go. Hope to finish this little gem come tomorrow.
Expect sound clips. There´s one of my old ones already up on YT. Just do a search for Geloso G.3215.
Be aware of the rather large difference in volume between speach and what´s played tho. So you don´t go deaf.
